1
|
Pleyerová I, Hamet J, Konrádová H, Lipavská H. Versatile roles of sorbitol in higher plants: luxury resource, effective defender or something else? PLANTA 2022; 256:13. [PMID: 35713726 DOI: 10.1007/s00425-022-03925-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Accepted: 05/21/2022] [Indexed: 06/15/2023]
Abstract
Sorbitol metabolism plays multiple roles in many plants, including energy and carbon enrichment, effective defence against various stresses and other emerging specific roles. The underlying mechanisms are, however, incompletely understood. This review provides the current state-of-the-art, highlights missing knowledge and poses several remaining questions. The basic properties of sugar alcohols are summarised and pathways of sorbitol metabolism, including biosynthesis, degradation and key enzymes are described. Sorbitol transport within the plant body is discussed and individual roles of sorbitol in different organs, specific cells or even cellular compartments, are elaborated, clarifying the critical importance of sorbitol allocation and distribution. In addition to plants that accumulate and transport significant quantities of sorbitol (usual producers), there are some that synthesize small amounts of sorbitol or only possess sorbitol metabolising enzymes (non-usual producers). Modern analytical methods have recently enabled large amounts of data to be acquired on this topic, although numerous uncertainties and questions remain. For a long time, it has been clear that enriching carbohydrate metabolism with a sorbitol branch improves plant fitness under stress. Nevertheless, this is probably valid only when appropriate growth and defence trade-offs are ensured. Information on the ectopic expression of sorbitol metabolism genes has contributed substantially to our understanding of the sorbitol roles and raises new questions regarding sorbitol signalling potential. We finally examine strategies in plants producing sorbitol compared with those producing mannitol. Providing an in-depth understanding of sugar alcohol metabolism is essential for the progress in plant physiology as well as in targeted, knowledge-based crop breeding.
Collapse
Affiliation(s)
- Iveta Pleyerová
- Department of Experimental Plant Biology, Faculty of Science, Charles University, Viničná 5, 128 43, Prague 2, Czech Republic
| | - Jaromír Hamet
- Department of Experimental Plant Biology, Faculty of Science, Charles University, Viničná 5, 128 43, Prague 2, Czech Republic
| | - Hana Konrádová
- Department of Experimental Plant Biology, Faculty of Science, Charles University, Viničná 5, 128 43, Prague 2, Czech Republic.
| | - Helena Lipavská
- Department of Experimental Plant Biology, Faculty of Science, Charles University, Viničná 5, 128 43, Prague 2, Czech Republic
| |
Collapse
|
2
|
Polutchko SK, Stewart JJ, Adams Iii WW, Demmig-Adams B. Photosynthesis and foliar vascular adjustments to growth light intensity in summer annual species with symplastic and apoplastic phloem loading. JOURNAL OF PLANT PHYSIOLOGY 2021; 267:153532. [PMID: 34638004 DOI: 10.1016/j.jplph.2021.153532] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 09/22/2021] [Indexed: 06/13/2023]
Abstract
Concomitant adjustments in photosynthetic capacity and size, composition, and/or density of minor foliar veins in response to growth environment were previously described primarily for winter annuals that load sugars into foliar phloem apoplastically. Here, common trends, differences associated with phloem-loading mechanism, and species-dependent differences are identified for summer annuals (loading sugars either symplastically [cucumber, pumpkin, and basil] or apoplastically [tomato and sunflower]) that were grown in low and high light. Photosynthetic capacity per leaf area was significantly positively correlated with leaf-level volume of phloem-loading cells (LCs), sugar-export conduits (sieve elements), and water conduits (tracheary elements) irrespective of phloem-loading mechanism. The relative contribution to leaf-level volume of LC numbers versus individual LC size was greater in apoplastic loaders than in symplastic loaders. Species-dependent differences included different vein density within each loading group and either greater or lower numbers of cells per minor vein (especially of tracheary elements in the symplastic loaders basil versus cucumber, respectively), which may be due to genetic adaptation to different environmental conditions. These results indicate considerable plasticity in foliar vascular features in summer annuals as well as some loading-mechanism-dependent trends.
Collapse
Affiliation(s)
- Stephanie K Polutchko
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.
| | - Jared J Stewart
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.
| | - William W Adams Iii
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.
| | - Barbara Demmig-Adams
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.
| |
Collapse
|
3
|
Ren Y, Li M, Guo S, Sun H, Zhao J, Zhang J, Liu G, He H, Tian S, Yu Y, Gong G, Zhang H, Zhang X, Alseekh S, Fernie AR, Scheller HV, Xu Y. Evolutionary gain of oligosaccharide hydrolysis and sugar transport enhanced carbohydrate partitioning in sweet watermelon fruits. THE PLANT CELL 2021; 33:1554-1573. [PMID: 33570606 PMCID: PMC8254481 DOI: 10.1093/plcell/koab055] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Accepted: 02/06/2021] [Indexed: 05/04/2023]
Abstract
How raffinose (Raf) family oligosaccharides, the major translocated sugars in the vascular bundle in cucurbits, are hydrolyzed and subsequently partitioned has not been fully elucidated. By performing reciprocal grafting of watermelon (Citrullus lanatus) fruits to branch stems, we observed that Raf was hydrolyzed in the fruit of cultivar watermelons but was backlogged in the fruit of wild ancestor species. Through a genome-wide association study, the alkaline alpha-galactosidase ClAGA2 was identified as the key factor controlling stachyose and Raf hydrolysis, and it was determined to be specifically expressed in the vascular bundle. Analysis of transgenic plants confirmed that ClAGA2 controls fruit Raf hydrolysis and reduces sugar content in fruits. Two single-nucleotide polymorphisms (SNPs) within the ClAGA2 promoter affect the recruitment of the transcription factor ClNF-YC2 (nuclear transcription factor Y subunit C) to regulate ClAGA2 expression. Moreover, this study demonstrates that C. lanatus Sugars Will Eventually Be Exported Transporter 3 (ClSWEET3) and Tonoplast Sugar Transporter (ClTST2) participate in plasma membrane sugar transport and sugar storage in fruit cell vacuoles, respectively. Knocking out ClAGA2, ClSWEET3, and ClTST2 affected fruit sugar accumulation. Genomic signatures indicate that the selection of ClAGA2, ClSWEET3, and ClTST2 for carbohydrate partitioning led to the derivation of modern sweet watermelon from non-sweet ancestors during domestication.
Collapse
Affiliation(s)
- Yi Ren
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
- Joint BioEnergy Institute and Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Maoying Li
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Shaogui Guo
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Honghe Sun
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Jianyu Zhao
- Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, MOE Joint International Research Laboratory of Crop Molecular Breeding, China Agricultural University, Beijing 100193, China
| | - Jie Zhang
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Guangmin Liu
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Hongju He
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Shouwei Tian
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Yongtao Yu
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Guoyi Gong
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Haiying Zhang
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| | - Xiaolan Zhang
- Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, MOE Joint International Research Laboratory of Crop Molecular Breeding, China Agricultural University, Beijing 100193, China
| | - Saleh Alseekh
- Max-Planck-Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
- Center of Plant System Biology and Biotechnology, 4000 Plovdiv, Bulgaria
| | - Alisdair R Fernie
- Max-Planck-Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
- Center of Plant System Biology and Biotechnology, 4000 Plovdiv, Bulgaria
| | - Henrik V Scheller
- Joint BioEnergy Institute and Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
- Department of Plant and Microbial Biology, University of California, Berkeley, California, USA
| | - Yong Xu
- National Watermelon and Melon Improvement Center, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
| |
Collapse
|
4
|
Zhang L, Wang L, Zhang J, Song C, Li Y, Li J, Lu M. Expression and localization of SWEETs in Populus and the effect of SWEET7 overexpression in secondary growth. TREE PHYSIOLOGY 2021; 41:882-899. [PMID: 33147625 DOI: 10.1093/treephys/tpaa145] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 10/29/2020] [Indexed: 06/11/2023]
Abstract
In trees, wood formation needs carbon import from the photosynthetic source tissues. Sugar transporters play important roles in carbohydrate transport into wood-forming cells. Sugars will eventually be exported transporters (SWEETs) play essential roles in many physiological processes. However, the roles of this family in the growth and development of woody plants have not been systematically investigated. In this study, 27 SWEET genes were identified in the Populus trichocarpa genome. These SWEET genes were classified into four clades based on their phylogenetic relationships, gene structures, conserved motifs and chromosomal locations. Representative SWEET members from each clade were selected for further studies. The PagSWEETs of Populus alba × Populus glandulosa were localized to plasma membrane, vacuolar, endoplasmic reticulum or Golgi. Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) analysis showed that PagSWEETs have distinct expression patterns in various tissues, and PagSWEET5, 7, 10b, 10c, 15b, 17a and 17c exhibited high expression levels in stems. PagSWEET7 is localized to the cytoplasmic membrane and specifically expressed in the phloem as detected by histochemical GUS ($\beta $ - glucuronidase) assays. Xylem production and xylem sugar content were greater in developing wood of PagSWEET7 overexpression than wild-type lines. Collectively, these results provide valuable information for further investigating functions of PagSWEET genes, and identify PagSWEET7 as a candidate gene for using biotechnology to modify the wood formation in poplar.
Collapse
Affiliation(s)
- Li Zhang
- State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
- College of Agricultural and Biological engineering, Heze University, Heze, Shandong 274015, China
| | - Lijuan Wang
- State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
- Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, China
| | - Jin Zhang
- State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
- State Key Laboratory of Subtropical Forestry, School of Forestry and Biotechnology, Zhejiang A&F University, Hangzhou 311300, Zhejiang, China
| | - Cai Song
- State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
- Key Laboratory of Non-wood Forest Product of State Forestry Administration, School of Forestry, Central South University of Forestry and Technology, Changsha 410004, China
| | - Yu Li
- State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
| | - Jianbo Li
- State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
| | - Mengzhu Lu
- State Key Laboratory of Tree Genetics and Breeding, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
- Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, China
- State Key Laboratory of Subtropical Forestry, School of Forestry and Biotechnology, Zhejiang A&F University, Hangzhou 311300, Zhejiang, China
| |
Collapse
|
5
|
Harding SA, Frost CJ, Tsai CJ. Defoliation-induced compensatory transpiration is compromised in SUT4-RNAi Populus. PLANT DIRECT 2020; 4:e00268. [PMID: 33015535 PMCID: PMC7522500 DOI: 10.1002/pld3.268] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Revised: 07/13/2020] [Accepted: 08/23/2020] [Indexed: 06/11/2023]
Abstract
The tonoplast sucrose transporter PtaSUT4 is well expressed in leaves of Populus tremula × Populus alba (INRA 717-IB4), and its inhibition by RNA-interference (RNAi) alters leaf sucrose homeostasis. Whether sucrose partitioning between the vacuole and the cytosol is modulated by PtaSUT4 for specific physiological outcomes in Populus remains unexplored. In this study, partial defoliation was used to elicit compensatory increases in photosynthesis and transpiration by the remaining leaves in greenhouse-grown poplar. Water uptake, leaf gas exchange properties, growth and nonstructural carbohydrate abundance in source and sink organs were then compared between wild-type and SUT4-RNAi lines. Partial defoliation increased maximum photosynthesis rates similarly in all lines. There was no indication that source leaf sugar levels changed differently between wild-type and RNAi plants following partial defoliation. Sink levels of hexose (glucose and fructose) and starch decreased similarly in all lines. Interestingly, plant water uptake after partial defoliation was not as well sustained in RNAi as in wild-type plants. While the compensatory increase in photosynthesis was similar between genotypes, leaf transpiration increased less robustly in RNAi than wild-type plants. SUT4-RNAi and wild-type source leaves differed constitutively in their bulk modulus of elasticity, a measure of leaf turgor, and storage water capacitance. The data demonstrate that reduced sucrose partitioning due to PtaSUT4-RNAi altered turgor control and compensatory transpiration capacity more strikingly than photosynthesis and sugar export. The results are consistent with the interpretation that SUT4 may control vacuolar turgor independently of sink carbon provisioning.
Collapse
Affiliation(s)
- Scott A Harding
- Warnell School of Forestry and Natural Resources Department of Genetics and Department of Plant Biology University of Georgia Athens GA USA
| | - Christopher J Frost
- Warnell School of Forestry and Natural Resources Department of Genetics and Department of Plant Biology University of Georgia Athens GA USA
- Present address: BIO5 Institute University of Arizona Tucson AZ 85719 USA
| | - Chung-Jui Tsai
- Warnell School of Forestry and Natural Resources Department of Genetics and Department of Plant Biology University of Georgia Athens GA USA
| |
Collapse
|
6
|
Young SNR, Sack L, Sporck-Koehler MJ, Lundgren MR. Why is C4 photosynthesis so rare in trees? JOURNAL OF EXPERIMENTAL BOTANY 2020; 71:4629-4638. [PMID: 32409834 PMCID: PMC7410182 DOI: 10.1093/jxb/eraa234] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 05/12/2020] [Indexed: 05/08/2023]
Abstract
Since C4 photosynthesis was first discovered >50 years ago, researchers have sought to understand how this complex trait evolved from the ancestral C3 photosynthetic machinery on >60 occasions. Despite its repeated emergence across the plant kingdom, C4 photosynthesis is notably rare in trees, with true C4 trees only existing in Euphorbia. Here we consider aspects of the C4 trait that could limit but not preclude the evolution of a C4 tree, including reduced quantum yield, increased energetic demand, reduced adaptive plasticity, evolutionary constraints, and a new theory that the passive symplastic phloem loading mechanism observed in trees, combined with difficulties in maintaining sugar and water transport over a long pathlength, could make C4 photosynthesis largely incompatible with the tree lifeform. We conclude that the transition to a tree habit within C4 lineages as well as the emergence of C4 photosynthesis within pre-existing trees would both face a series of challenges that together explain the global rarity of C4 photosynthesis in trees. The C4 trees in Euphorbia are therefore exceptional in how they have circumvented every potential barrier to the rare C4 tree lifeform.
Collapse
Affiliation(s)
- Sophie N R Young
- Lancaster Environment Centre, Lancaster University, Lancaster, UK
| | - Lawren Sack
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, USA
| | | | - Marjorie R Lundgren
- Lancaster Environment Centre, Lancaster University, Lancaster, UK
- Correspondence:
| |
Collapse
|
7
|
Schneider K, Abazaj L, Niemann C, Schröder L, Nägele T. Cold acclimation has a differential effect on leaf vascular bundle structure and carbon export rates in natural Arabidopsis accessions originating from southern and northern Europe. PLANT DIRECT 2020; 4:e00251. [PMID: 32789285 PMCID: PMC7416751 DOI: 10.1002/pld3.251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 07/08/2020] [Accepted: 07/16/2020] [Indexed: 06/11/2023]
Abstract
Acclimation to low but non-freezing temperature represents an ecologically important process for Arabidopsis thaliana but also for many other plant species from temperate regions. Cold acclimation comprises and affects numerous molecular and physiological processes and the maintenance of sugar supply of sink tissue by photosynthetically active source tissue is essential for plant survival. Here, changes in vascular bundle (VB) structure at the leaf petiole were analysed together with sucrose exudation rates before and after cold acclimation. Six natural Arabidopsis accessions originating from southern and northern Europe were compared. Photosynthetic efficiency, that is, maximum and effective quantum yield of photosystem II, revealed a significant effect of environmental condition. Only for northern accessions was a highly significant negative correlation observed between leaf sucrose exudation rates, xylem, and petiole cross-sectional areas. Furthermore, only for northern accessions was a significant increase of VB and leaf petiole cross-sectional area observed during cold acclimation. In contrast, variance of cross-sectional areas of cold acclimated southern accessions was strongly reduced compared to control plants, while mean areas remained similar under both conditions. In summary, these findings suggest that natural Arabidopsis accessions from northern Europe significantly adjust sink strength and leaf VB structure to maintain plant growth and photosynthesis under low temperature.
Collapse
Affiliation(s)
- Katja Schneider
- Department Biology IPlant DevelopmentLMU MünchenPlanegg‐MartinsriedGermany
| | - Lorena Abazaj
- Department Biology IPlant Evolutionary Cell BiologyLMU MünchenPlanegg‐MartinsriedGermany
| | - Cornelia Niemann
- Department Biology IPlant DevelopmentLMU MünchenPlanegg‐MartinsriedGermany
| | - Laura Schröder
- Department Biology IPlant Evolutionary Cell BiologyLMU MünchenPlanegg‐MartinsriedGermany
| | - Thomas Nägele
- Department Biology IPlant Evolutionary Cell BiologyLMU MünchenPlanegg‐MartinsriedGermany
| |
Collapse
|
8
|
Furze ME, Drake JE, Wiesenbauer J, Richter A, Pendall E. Carbon isotopic tracing of sugars throughout whole-trees exposed to climate warming. PLANT, CELL & ENVIRONMENT 2019; 42:3253-3263. [PMID: 31335973 DOI: 10.1111/pce.13625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 07/16/2019] [Accepted: 07/18/2019] [Indexed: 06/10/2023]
Abstract
Trees allocate C from sources to sinks by way of a series of processes involving carbohydrate transport and utilization. Yet these dynamics are not well characterized in trees, and it is unclear how these dynamics will respond to a warmer world. Here, we conducted a warming and pulse-chase experiment on Eucalyptus parramattensis growing in a whole-tree chamber system to test whether warming impacts carbon allocation by increasing the speed of carbohydrate dynamics. We pulse-labelled large (6-m tall) trees with 13 C-CO2 to follow recently fixed C through different organs by using compound-specific isotope analysis of sugars. We then compared concentrations and mean residence times of individual sugars between ambient and warmed (+3°C) treatments. Trees dynamically allocated 13 C-labelled sugars throughout the aboveground-belowground continuum. We did not, however, find a significant treatment effect on C dynamics, as sugar concentrations and mean residence times were not altered by warming. From the canopy to the root system, 13 C enrichment of sugars decreased, and mean residence times increased, reflecting dilution and mixing of recent photoassimilates with older reserves along the transport pathway. Our results suggest that a locally endemic eucalypt was seemingly able to adjust its physiology to warming representative of future temperature predictions for Australia.
Collapse
Affiliation(s)
- Morgan E Furze
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138
| | - John E Drake
- Department of Forest and Natural Resources Management, College of Environmental Science and Forestry, State University of New York, Syracuse, New York, 13210
| | - Julia Wiesenbauer
- Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, 1010, Austria
| | - Andreas Richter
- Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, 1010, Austria
| | - Elise Pendall
- Hawkesbury Institute for the Environment, Western Sydney University, Penrith, New South Wales, 2751, Australia
| |
Collapse
|
9
|
Salmon Y, Dietrich L, Sevanto S, Hölttä T, Dannoura M, Epron D. Drought impacts on tree phloem: from cell-level responses to ecological significance. TREE PHYSIOLOGY 2019; 39:173-191. [PMID: 30726983 DOI: 10.1093/treephys/tpy153] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Revised: 12/03/2018] [Accepted: 01/25/2019] [Indexed: 06/09/2023]
Abstract
On-going climate change is increasing the risk of drought stress across large areas worldwide. Such drought events decrease ecosystem productivity and have been increasingly linked to tree mortality. Understanding how trees respond to water shortage is key to predicting the future of ecosystem functions. Phloem is at the core of the tree functions, moving resources such as non-structural carbohydrates, nutrients, and defence and information molecules across the whole plant. Phloem function and ability to transport resources is tightly controlled by the balance of carbon and water fluxes within the tree. As such, drought is expected to impact phloem function by decreasing the amount of available water and new photoassimilates. Yet, the effect of drought on the phloem has received surprisingly little attention in the last decades. Here we review existing knowledge on drought impacts on phloem transport from loading and unloading processes at cellular level to possible effects on long-distance transport and consequences to ecosystems via ecophysiological feedbacks. We also point to new research frontiers that need to be explored to improve our understanding of phloem function under drought. In particular, we show how phloem transport is affected differently by increasing drought intensity, from no response to a slowdown, and explore how severe drought might actually disrupt the phloem transport enough to threaten tree survival. Because transport of resources affects other organisms interacting with the tree, we also review the ecological consequences of phloem response to drought and especially predatory, mutualistic and competitive relations. Finally, as phloem is the main path for carbon from sources to sink, we show how drought can affect biogeochemical cycles through changes in phloem transport. Overall, existing knowledge is consistent with the hypotheses that phloem response to drought matters for understanding tree and ecosystem function. However, future research on a large range of species and ecosystems is urgently needed to gain a comprehensive understanding of the question.
Collapse
Affiliation(s)
- Yann Salmon
- Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, Gustaf Hällströmin katu 2b, University of Helsinki, Helsinki, Finland
- Institute for Atmospheric and Earth System Research/Forest Sciences, Faculty of Agriculture and Forestry, Latokartanonkaari 7, University of Helsinki, Helsinki, Finland
| | - Lars Dietrich
- Department of Environmental Sciences, University of Basel, Schönbeinstrasse 6, Basel, Switzerland
| | - Sanna Sevanto
- Earth and Environmental Sciences Division, Los Alamos National Laboratory, PO Box 1663 MA 495, Los Alamos, NM, USA
| | - Teemu Hölttä
- Institute for Atmospheric and Earth System Research/Forest Sciences, Faculty of Agriculture and Forestry, Latokartanonkaari 7, University of Helsinki, Helsinki, Finland
| | - Masako Dannoura
- Kyoto University, Laboratory of Ecosystem Production and Dynamics, Graduate School of Global Environmental Studies, Kyoto, Japan
- Kyoto University, Laboratory of Forest Utilization, Graduate School of Agriculture, Kyoto, Japan
| | - Daniel Epron
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
| |
Collapse
|
10
|
Epron D, Dannoura M, Hölttä T. Introduction to the invited issue on phloem function and dysfunction. TREE PHYSIOLOGY 2019; 39:167-172. [PMID: 30785633 DOI: 10.1093/treephys/tpz007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 01/08/2019] [Accepted: 01/15/2019] [Indexed: 06/09/2023]
Affiliation(s)
- Daniel Epron
- Université de Lorraine, AgroParisTech, INRA, UMR Silva, Faculté des Sciences et Technologies, Nancy, France
| | - Masako Dannoura
- Kyoto University, Laboratory of Ecosystem Production and Dynamics, Graduate School of Global Environmental Studies, Kyoto, Japan
- Kyoto University, Laboratory of Forest Utilization, Graduate School of Agriculture, Kyoto, Japan
| | - Teemu Hölttä
- Institute for Atmospheric and Earth System Research/Forest Sciences, Faculty of Agriculture and Forestry, Latokartanonkaari 7, University of Helsinki, Helsinki, Finland
| |
Collapse
|
11
|
Losada JM, Holbrook NM. Scaling of phloem hydraulic resistance in stems and leaves of the understory angiosperm shrub Illicium parviflorum. AMERICAN JOURNAL OF BOTANY 2019; 106:244-259. [PMID: 30793276 DOI: 10.1002/ajb2.1241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 12/05/2018] [Indexed: 06/09/2023]
Abstract
PREMISE OF THE STUDY Recent studies in canopy-dominant trees revealed axial scaling of phloem structure. However, whether this pattern is found in woody plants of the understory, the environment of most angiosperms from the ANA grade (Amborellales-Nymphaeales-Austrobaileyales), is unknown. METHODS We used seedlings and adult plants of the understory tropical shrub Illicium parviflorum, a member of the lineage Austrobaileyales, to explore the anatomy and physiology of the phloem in their aerial parts, including changes through ontogeny. KEY RESULTS Adult plants maintain a similar proportion of phloem tissue across stem diameters, but larger conduit dimensions and number cause the hydraulic resistance of the phloem to decrease toward the base of the plant. Small sieve plate pores resulted in an overall higher sieve tube hydraulic resistance than has been reported in other woody angiosperms. Sieve elements increase in size from minor to major leaf veins, but were shorter and narrower in petioles. The low carbon assimilation rates of seedlings and mature plants contrasted with a 3-fold higher phloem sap velocity in seedlings, suggesting that phloem transport velocity is modulated through ontogeny. CONCLUSIONS The overall architecture of the phloem tissue in this understory angiosperm shrub scales in a manner consistent with taller trees that make up the forest canopy. Thus, the evolution of larger sieve plate pores in canopy-dominant trees may have played a key role in allowing woody angiosperms to extend beyond their understory origins.
Collapse
Affiliation(s)
- Juan M Losada
- Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA, 02138, USA
- Arnold Arboretum of Harvard University, 1300 Centre St., Boston, MA, 02130, USA
| | - N Michele Holbrook
- Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA, 02138, USA
- Arnold Arboretum of Harvard University, 1300 Centre St., Boston, MA, 02130, USA
| |
Collapse
|
12
|
Fink D, Dobbelstein E, Barbian A, Lohaus G. Ratio of sugar concentrations in the phloem sap and the cytosol of mesophyll cells in different tree species as an indicator of the phloem loading mechanism. PLANTA 2018; 248:661-673. [PMID: 29882156 DOI: 10.1007/s00425-018-2933-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Accepted: 06/01/2018] [Indexed: 05/28/2023]
Abstract
Sucrose concentration in phloem sap was several times higher than in the cytosol of mesophyll cells. The results suggest that phloem loading involves active steps in the analyzed tree species. Phloem loading in source leaves is a key step for carbon partitioning and passive symplastic loading has been proposed for several tree species. However, experimental evidence to prove the potential for sucrose diffusion from mesophyll to phloem is rare. Here, we analyzed three tree species (two angiosperms, Fagus sylvatica, Magnolia kobus, and one gymnosperm, Gnetum gnemon) to investigate the proposed phloem loading mechanism. For this purpose, the minor vein structure and the sugar concentrations in phloem sap as well as in the subcellular compartments of mesophyll cells were investigated. The analyzed tree species belong to the open type minor vein subcategory. The sucrose concentration in the cytosol of mesophyll cells ranged between 75 and 165 mM and was almost equal to the vacuolar concentration. Phloem sap could be collected from F. sylvatica and M. kobus and the concentration of sucrose in phloem sap was about five- and 11-fold higher, respectively, than in the cytosol of mesophyll cells. Sugar exudation of cut leaves was decreased by p-chloromercuribenzenesulfonic acid, an inhibitor of sucrose-proton transporter. The results suggest that phloem loading of sucrose in the analyzed tree species involves active steps, and apoplastic phloem loading seems more likely.
Collapse
Affiliation(s)
- Daniel Fink
- Molecular Plant Science/Plant Biochemistry, University of Wuppertal, Wuppertal, Germany
| | - Elena Dobbelstein
- Molecular Plant Science/Plant Biochemistry, University of Wuppertal, Wuppertal, Germany
| | - Andreas Barbian
- Core Facility Electron Microscopy, UKD, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Gertrud Lohaus
- Molecular Plant Science/Plant Biochemistry, University of Wuppertal, Wuppertal, Germany.
| |
Collapse
|
13
|
Abstract
The phloem plays a central role in transporting resources and signalling molecules from fully expanded leaves to provide precursors for, and to direct development of, heterotrophic organs located throughout the plant body. We review recent advances in understanding mechanisms regulating loading and unloading of resources into, and from, the phloem network; highlight unresolved questions regarding the physiological significance of the vast array of proteins and RNAs found in phloem saps; and evaluate proposed structure/function relationships considered to account for bulk flow of sap, sustained at high rates and over long distances, through the transport phloem.
Collapse
Affiliation(s)
- Johannes Liesche
- Biomass Energy Center for Arid and Semi-arid lands, Northwest A&F University, Yangling, China
- College of Life Science, Northwest A&F University, Yangling , China
| | - John Patrick
- Department of Biological Sciences, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, Australia
| |
Collapse
|
14
|
Nguyen STT, McCurdy DW. Wall ingrowth deposition in phloem parenchyma transfer cells in Arabidopsis: Heteroblastic variations and a potential role in pathogen defence. PLANT SIGNALING & BEHAVIOR 2017; 12:e1338226. [PMID: 28594274 PMCID: PMC5566348 DOI: 10.1080/15592324.2017.1338226] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Accepted: 05/29/2017] [Indexed: 05/17/2023]
Abstract
Transfer cell (TCs) develop unique wall ingrowth networks which amplify plasma membrane surface area and thus maximize nutrient transporter density at key anatomic sites for nutrient exchange within plants and their external environment. These sites fall into 4 main groups corresponding to 4 categories of trans-membrane flux: absorption/secretion of solutes from or to the external environment, and absorption/secretion of solutes from or to internal, extra-cytoplasmic compartments. Research on TC biology over recent decades has demonstrated correlations between wall ingrowth deposition in TCs and enhanced transport capacity in many major agricultural species such as pea, fava bean, cotton and maize. Consequently, there is general consensus that the existence of wall ingrowth morphology implies an augmentation in membrane transport capacity. However, this may not be entirely applicable for phloem parenchyma (PP) TCs in Arabidopsis. Our recent survey of PP TC abundance and distribution in Arabidopsis veins indicated that PP TC development reflects heteroblastic status. A consequence of this observation is the suggestion that PP TCs, or at least wall ingrowth deposition in these cells, potentially act as a physical barrier to defend access of invading pathogens to sugar-rich sieve elements rather than solely in facilitating the export of photoassimilate from collection phloem in leaves.
Collapse
Affiliation(s)
- Suong T. T. Nguyen
- Centre for Plant Science, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW, Australia
- Department of Biological Sciences, Faculty of Sciences, Nong Lam University, HCMC, Vietnam
| | - David W. McCurdy
- Centre for Plant Science, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW, Australia
- CONTACT David W. McCurdy School of Environmental and Life Sciences, The University of Newcastle, University Dr. Callaghan, Newcastle, NSW 2308, Australia
| |
Collapse
|
15
|
Liesche J. Sucrose transporters and plasmodesmal regulation in passive phloem loading. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2017; 59:311-321. [PMID: 28429873 DOI: 10.1111/jipb.12548] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Accepted: 04/21/2017] [Indexed: 06/07/2023]
Abstract
An essential step for the distribution of carbon throughout the whole plant is the loading of sugars into the phloem in source organs. In many plants, accumulation of sugars in the sieve element-companion cell (SE-CC) complex is mediated and regulated by active processes. However, for poplar and many other tree species, a passive symplasmic mechanism of phloem loading has been proposed, characterized by symplasmic continuity along the pre-phloem pathway and the absence of active sugar accumulation in the SE-CC complex. A high overall leaf sugar concentration is thought to enable diffusion of sucrose into the phloem. In this review, we critically evaluate current evidence regarding the mechanism of passive symplasmic phloem loading, with a focus on the potential influence of active sugar transport and plasmodesmal regulation. The limited experimental data, combined with theoretical considerations, suggest that a concomitant operation of passive symplasmic and active phloem loading in the same minor vein is unlikely. However, active sugar transport could well play an important role in how passively loading plants might modulate the rate of sugar export from leaves. Insights into the operation of this mechanism has direct implications for our understanding of how these plants utilize assimilated carbon.
Collapse
Affiliation(s)
- Johannes Liesche
- College of Life Science, Northwest A&F University, No 3 Taicheng Road, Yangling 712100, China
- Biomass Energy Center for Arid and Semi-arid lands, Northwest A&F University, Yangling 712100, China
| |
Collapse
|
16
|
Figueroa C, Piattoni C, Trípodi K, Podestá F, Iglesias A. Carbon Photoassimilation and Photosynthate Partitioning in Plants. ACTA ACUST UNITED AC 2016. [DOI: 10.1201/b19498-38] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
|
17
|
Savage JA, Clearwater MJ, Haines DF, Klein T, Mencuccini M, Sevanto S, Turgeon R, Zhang C. Allocation, stress tolerance and carbon transport in plants: how does phloem physiology affect plant ecology? PLANT, CELL & ENVIRONMENT 2016; 39:709-25. [PMID: 26147312 DOI: 10.1111/pce.12602] [Citation(s) in RCA: 104] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Revised: 05/30/2015] [Accepted: 06/19/2015] [Indexed: 05/02/2023]
Abstract
Despite the crucial role of carbon transport in whole plant physiology and its impact on plant-environment interactions and ecosystem function, relatively little research has tried to examine how phloem physiology impacts plant ecology. In this review, we highlight several areas of active research where inquiry into phloem physiology has increased our understanding of whole plant function and ecological processes. We consider how xylem-phloem interactions impact plant drought tolerance and reproduction, how phloem transport influences carbon allocation in trees and carbon cycling in ecosystems and how phloem function mediates plant relations with insects, pests, microbes and symbiotes. We argue that in spite of challenges that exist in studying phloem physiology, it is critical that we consider the role of this dynamic vascular system when examining the relationship between plants and their biotic and abiotic environment.
Collapse
Affiliation(s)
- Jessica A Savage
- Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA, 02131, USA
| | | | - Dustin F Haines
- Department of Environmental Conservation, University of Massachusetts, 160 Holdsworth Way, Amherst, MA, 01003, USA
| | - Tamir Klein
- Institute of Botany, University of Basel, Schoenbeinstrasse 6, 4056, Basel, Switzerland
| | - Maurizio Mencuccini
- School of GeoSciences, University of Edinburgh, Crew Building, West Mains Road, EH9 3JN, Edinburgh, UK
- ICREA at CREAF, Campus de UAB, Cerdanyola del Valles, Barcelona, 08023, Spain
| | - Sanna Sevanto
- Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA
| | - Robert Turgeon
- Plant Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, 14853, USA
| | - Cankui Zhang
- Department of Agronomy, Purdue University, West Lafayette, IN, 47907, USA
| |
Collapse
|
18
|
Turgeon R. Phloem Biology of the Cucurbitaceae. GENETICS AND GENOMICS OF CUCURBITACEAE 2016. [DOI: 10.1007/7397_2016_23] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
|
19
|
Liesche J. How regulation of phloem transport could link potassium fertilization to increased growth. TREE PHYSIOLOGY 2016; 36:1-5. [PMID: 26612849 DOI: 10.1093/treephys/tpv120] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 10/13/2015] [Indexed: 06/05/2023]
Affiliation(s)
- Johannes Liesche
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| |
Collapse
|
20
|
Milne RJ, Offler CE, Patrick JW, Grof CPL. Cellular pathways of source leaf phloem loading and phloem unloading in developing stems of Sorghum bicolor in relation to stem sucrose storage. FUNCTIONAL PLANT BIOLOGY : FPB 2015; 42:957-970. [PMID: 32480736 DOI: 10.1071/fp15133] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Accepted: 06/25/2015] [Indexed: 06/11/2023]
Abstract
Cellular pathways of phloem loading in source leaves and phloem unloading in stems of sweet Sorghum bicolor (L.) Moench were deduced from histochemical determinations of cell wall composition and from the relative radial mobilities of fluorescent tracer dyes exiting vascular pipelines. The cell walls of small vascular bundles in source leaves, the predicted site of phloem loading, contained minimal quantities of lignin and suberin. A phloem-loaded symplasmic tracer, carboxyfluorescein, was retained within the collection phloem, indicating symplasmic isolation. Together, these findings suggested that phloem loading in source leaves occurs apoplasmically. Lignin was restricted to the walls of protoxylem elements located in meristematic, elongating and recently elongated regions of the stem. The apoplasmic tracer, 8-hydroxypyrene-1,3,6-trisulfonic acid, moved radially from the transpiration stream, consistent with phloem and storage parenchyma cells being interconnected by an apoplasmic pathway. The major phase of sucrose accumulation in mature stems coincided with heavy lignification and suberisation of sclerenchyma sheath cell walls restricting apoplasmic tracer movement from the phloem to storage parenchyma apoplasms. Phloem unloading at this stage of stem development followed a symplasmic route linking sieve elements and storage parenchyma cells, as confirmed by the phloem-delivered symplasmic tracer, 8-hydroxypyrene-1,3,6-trisulfonic acid, moving radially from the stem phloem.
Collapse
Affiliation(s)
- Ricky J Milne
- School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Christina E Offler
- School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia
| | - John W Patrick
- School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia
| | - Christopher P L Grof
- School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia
| |
Collapse
|
21
|
Öner-Sieben S, Rappl C, Sauer N, Stadler R, Lohaus G. Characterization, localization, and seasonal changes of the sucrose transporter FeSUT1 in the phloem of Fraxinus excelsior. JOURNAL OF EXPERIMENTAL BOTANY 2015; 66:4807-19. [PMID: 26022258 PMCID: PMC4507781 DOI: 10.1093/jxb/erv255] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Trees are generally assumed to be symplastic phloem loaders. A typical feature for most wooden species is an open minor vein structure with symplastic connections between mesophyll cells and phloem cells, which allow sucrose to move cell-to-cell through the plasmodesmata into the phloem. Fraxinus excelsior (Oleaceae) also translocates raffinose family oligosaccharides in addition to sucrose. Sucrose concentration was recently shown to be higher in the phloem sap than in the mesophyll cells. This suggests the involvement of apoplastic steps and the activity of sucrose transporters in addition to symplastic phloem-loading processes. In this study, the sucrose transporter FeSUT1 from F. excelsior was analysed. Heterologous expression in baker's yeast showed that FeSUT1 mediates the uptake of sucrose. Immunohistochemical analyses revealed that FeSUT1 was exclusively located in phloem cells of minor veins and in the transport phloem of F. excelsior. Further characterization identified these cells as sieve elements and possibly ordinary companion cells but not as intermediary cells. The localization and expression pattern point towards functions of FeSUT1 in phloem loading of sucrose as well as in sucrose retrieval. FeSUT1 is most likely responsible for the observed sucrose gradient between mesophyll and phloem. The elevated expression level of FeSUT1 indicated an increased apoplastic carbon export activity from the leaves during spring and late autumn. It is hypothesized that the importance of apoplastic loading is high under low-sucrose conditions and that the availability of two different phloem-loading mechanisms confers advantages for temperate woody species like F. excelsior.
Collapse
Affiliation(s)
- Soner Öner-Sieben
- Molekulare Pflanzenforschung/Pflanzenbiochemie (Botanik), Bergische Universität Wuppertal, Gaußstraße 20, D-42119 Wuppertal, Germany
| | - Christine Rappl
- Lehrstuhl Molekulare Pflanzenphysiologie Department Biologie, Universität Erlangen-Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany
| | - Norbert Sauer
- Lehrstuhl Molekulare Pflanzenphysiologie Department Biologie, Universität Erlangen-Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany
| | - Ruth Stadler
- Lehrstuhl Molekulare Pflanzenphysiologie Department Biologie, Universität Erlangen-Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany
| | - Gertrud Lohaus
- Molekulare Pflanzenforschung/Pflanzenbiochemie (Botanik), Bergische Universität Wuppertal, Gaußstraße 20, D-42119 Wuppertal, Germany
| |
Collapse
|
22
|
Schulz A. Diffusion or bulk flow: how plasmodesmata facilitate pre-phloem transport of assimilates. JOURNAL OF PLANT RESEARCH 2015; 128:49-61. [PMID: 25516499 DOI: 10.1007/s10265-014-0676-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2014] [Accepted: 10/14/2014] [Indexed: 05/11/2023]
Abstract
Assimilates synthesized in the mesophyll of mature leaves move along the pre-phloem transport pathway to the bundle sheath of the minor veins from which they are loaded into the phloem. The present review discusses the most probable driving force(s) for the pre-phloem pathway, diffusion down the concentration gradient or bulk flow along a pressure gradient. The driving force seems to depend on the mode of phloem loading. In a majority of plant species phloem loading is a thermodynamically active process, involving the activity of membrane transporters in the sieve-element companion cell complex. Since assimilate movement includes an apoplasmic step, this mode is called apoplasmic loading. Well established is also the polymer-trap loading mode, where the phloem-transport sugars are raffinose-family oligomers in herbaceous plants. Also this mode depends on the investment of energy, here for sugar oligomerization, and leads to a high sugar accumulation in the phloem, even though the phloem is not symplasmically isolated, but well coupled by plasmodesmata (PD). Hence the mode polymer-trap mode is also designated active symplasmic loading. For woody angiosperms and gymnosperms an alternate loading mode is currently matter of discussion, called passive symplasmic loading. Based on the limited material available, this review compares the different loading modes and suggests that diffusion is the driving force in apoplasmic loaders, while bulk flow plays an increasing role in plants having a continuous symplasmic pathway from mesophyll to sieve elements. Crucial for the driving force is the question where water enters the pre-phloem pathway. Surprisingly, the role of PD in water movement has not been addressed so far appropriately. Modeling of assimilate and water fluxes indicates that in symplasmic loaders a considerable part of water flux happens through the PD between bundle sheath and phloem.
Collapse
Affiliation(s)
- Alexander Schulz
- Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871, Frederiksberg C, Denmark,
| |
Collapse
|
23
|
Öner-Sieben S, Lohaus G. Apoplastic and symplastic phloem loading in Quercus robur and Fraxinus excelsior. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:1905-16. [PMID: 24591056 PMCID: PMC3978624 DOI: 10.1093/jxb/eru066] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Whereas most of the research on phloem loading is performed on herbaceous plants, less is known about phloem loading strategies in trees. In this study, the phloem loading mechanisms of Quercus robur and Fraxinus excelsior were analysed. The following features were examined: the minor vein structure, the sugar concentrations in phloem sap by the laser-aphid-stylet technique, the distribution of photoassimilates in the mesophyll cells by non-aqueous fractionation, gradients of sugar concentrations and osmotic pressure, and the expression of sucrose transporters. The minor vein configurations of Q. robur and F. excelsior belong to the open type. Quercus robur contained companion cells in the minor veins whereas F. excelsior showed intermediary cells in addition to ordinary companion cells. The main carbon transport form in Q. robur was sucrose (~1M). In F. excelsior high amounts of raffinose and stachyose were also transported. However, in both tree species, the osmolality of phloem sap was higher than the osmolality of the mesophyll cells. The concentration gradients between phloem sap and the cytoplasm of mesophyll cells for sucrose were 16-fold and 14-fold for Q. robur and F. excelsior, respectively. Independent of the type of translocated sugars, sucrose transporter cDNAs were cloned from both species. The results indicate that phloem loading of sucrose and other metabolites must involve active loading steps in both tree species. Quercus robur seems to be an apoplastic phloem loader while F. excelsior shows indications of being a symplastic or mixed symplastic-apoplastic phloem loader.
Collapse
|
24
|
Lemoine R, Camera SL, Atanassova R, Dédaldéchamp F, Allario T, Pourtau N, Bonnemain JL, Laloi M, Coutos-Thévenot P, Maurousset L, Faucher M, Girousse C, Lemonnier P, Parrilla J, Durand M. Source-to-sink transport of sugar and regulation by environmental factors. FRONTIERS IN PLANT SCIENCE 2013; 4:272. [PMID: 23898339 PMCID: PMC3721551 DOI: 10.3389/fpls.2013.00272] [Citation(s) in RCA: 530] [Impact Index Per Article: 48.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2013] [Accepted: 07/02/2013] [Indexed: 05/18/2023]
Abstract
Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose (and some other sugars such as raffinose and polyols) across plant organs through the phloem. However, sugar transport through the phloem can be affected by many environmental factors that alter source/sink relationships. In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic (water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants) and biotic (mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants) factors. Concerning abiotic constraints, alteration of the distribution of sugar among sinks is often reported, with some sinks as roots favored in case of mineral deficiency. Many of these constraints impair the transport function of the phloem but the exact mechanisms are far from being completely known. Phloem integrity can be disrupted (e.g., by callose deposition) and under certain conditions, phloem transport is affected, earlier than photosynthesis. Photosynthesis inhibition could result from the increase in sugar concentration due to phloem transport decrease. Biotic interactions (aphids, fungi, viruses…) also affect crop plant productivity. Recent breakthroughs have identified some of the sugar transporters involved in these interactions on the host and pathogen sides. The different data are discussed in relation to the phloem transport pathways. When possible, the link with current knowledge on the pathways at the molecular level will be highlighted.
Collapse
Affiliation(s)
- Remi Lemoine
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Sylvain La Camera
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Rossitza Atanassova
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Fabienne Dédaldéchamp
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Thierry Allario
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Nathalie Pourtau
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Jean-Louis Bonnemain
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Maryse Laloi
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Pierre Coutos-Thévenot
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Laurence Maurousset
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Mireille Faucher
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Christine Girousse
- Diversité et Ecophysiologie des Céréales, Unités Mixtes de RechercheClermont Ferrand, France
| | - Pauline Lemonnier
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Jonathan Parrilla
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| | - Mickael Durand
- Unités Mixtes de Recherche, Ecologie et Biologie des Interactions, Université of Poitiers/Centre National de la Recherche ScientifiquePoitiers, France
| |
Collapse
|
25
|
Andriunas FA, Zhang HM, Xia X, Patrick JW, Offler CE. Intersection of transfer cells with phloem biology-broad evolutionary trends, function, and induction. FRONTIERS IN PLANT SCIENCE 2013; 4:221. [PMID: 23847631 PMCID: PMC3696738 DOI: 10.3389/fpls.2013.00221] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Accepted: 06/07/2013] [Indexed: 05/18/2023]
Abstract
Transfer cells (TCs) are ubiquitous throughout the plant kingdom. Their unique ingrowth wall labyrinths, supporting a plasma membrane enriched in transporter proteins, provides these cells with an enhanced membrane transport capacity for resources. In certain plant species, TCs have been shown to function to facilitate phloem loading and/or unloading at cellular sites of intense resource exchange between symplasmic/apoplasmic compartments. Within the phloem, the key cellular locations of TCs are leaf minor veins of collection phloem and stem nodes of transport phloem. In these locations, companion and phloem parenchyma cells trans-differentiate to a TC morphology consistent with facilitating loading and re-distribution of resources, respectively. At a species level, occurrence of TCs is significantly higher in transport than in collection phloem. TCs are absent from release phloem, but occur within post-sieve element unloading pathways and particularly at interfaces between generations of developing Angiosperm seeds. Experimental accessibility of seed TCs has provided opportunities to investigate their inductive signaling, regulation of ingrowth wall formation and membrane transport function. This review uses this information base to explore current knowledge of phloem transport function and inductive signaling for phloem-associated TCs. The functional role of collection phloem and seed TCs is supported by definitive evidence, but no such information is available for stem node TCs that present an almost intractable experimental challenge. There is an emerging understanding of inductive signals and signaling pathways responsible for initiating trans-differentiation to a TC morphology in developing seeds. However, scant information is available to comment on a potential role for inductive signals (auxin, ethylene and reactive oxygen species) that induce seed TCs, in regulating induction of phloem-associated TCs. Biotic phloem invaders have been used as a model to speculate on involvement of these signals.
Collapse
Affiliation(s)
| | | | | | | | - Christina E. Offler
- Department of Biological Sciences, School of Environmental and Life Sciences, The University of NewcastleCallaghan, NSW, Australia
| |
Collapse
|
26
|
Liesche J, Schulz A. Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders. FRONTIERS IN PLANT SCIENCE 2013; 4:207. [PMID: 23802006 PMCID: PMC3685819 DOI: 10.3389/fpls.2013.00207] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Accepted: 05/31/2013] [Indexed: 05/05/2023]
Abstract
Plasmodesmata (PD) play a key role in loading of sugars into the phloem. In plant species that employ the so-called active symplasmic loading strategy, sucrose that diffuses into their unique intermediary cells (ICs) is converted into sugar oligomers. According to the prevalent hypothesis, the oligomers are too large to pass back through PD on the bundle sheath side, but can pass on into the sieve element to be transported in the phloem. Here, we investigate if the PD at the bundle sheath-IC interface can indeed fulfill the function of blocking transport of sugar oligomers while still enabling efficient diffusion of sucrose. Hindrance factors are derived via theoretical modeling for different PD substructure configurations: sub-nano channels, slit, and hydrogel. The results suggest that a strong discrimination could only be realized when the PD opening is almost as small as the sugar oligomers. In order to find model parameters that match the in vivo situation, we measured the effective diffusion coefficient across the interface in question in Cucurbita pepo with 3D-photoactivation microscopy. Calculations indicate that a PD substructure of several sub-nano channels with a radius around 7 Å, a 10.4 Å-wide slit or a hydrogel with 49% polymer fraction would be compatible with the effective diffusion coefficient. If these configurations can accommodate sufficient flux of sucrose into the IC, while blocking raffinose and stachyose movement was assessed using literature data. While the slit-configuration would efficiently prevent the sugar oligomers from "leaking" from the IC, none of the configurations could enable a diffusion-driven sucrose flux that matches the reported rates at a physiologically relevant concentration potential. The presented data provides a first insight on how the substructure of PD could enable selective transport, but indicates that additional factors are involved in efficient phloem loading in active symplasmic loading species.
Collapse
Affiliation(s)
- Johannes Liesche
- Department of Plant and Environmental Sciences, University of CopenhagenCopenhagen, Denmark
| | | |
Collapse
|
27
|
Jensen KH, Savage JA, Holbrook NM. Optimal concentration for sugar transport in plants. J R Soc Interface 2013; 10:20130055. [PMID: 23516065 PMCID: PMC3645415 DOI: 10.1098/rsif.2013.0055] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2013] [Accepted: 02/25/2013] [Indexed: 11/12/2022] Open
Abstract
Vascular plants transport energy in the form of sugars from the leaves where they are produced to sites of active growth. The mass flow of sugars through the phloem vascular system is determined by the sap flow rate and the sugar concentration. If the concentration is low, little energy is transferred from source to sink. If it is too high, sap viscosity impedes flow. An interesting question is therefore at which concentration is the sugar flow optimal. Optimization of sugar flow and transport efficiency predicts optimal concentrations of 23.5 per cent (if the pressure differential driving the flow is independent of concentration) and 34.5 per cent (if the pressure is proportional to concentration). Data from more than 50 experiments (41 species) collected from the literature show an average concentration in the range from 18.2 per cent (all species) to 21.1 per cent (active loaders), suggesting that the phloem vasculature is optimized for efficient transport at constant pressure and that active phloem loading may have developed to increase transport efficiency.
Collapse
Affiliation(s)
- Kaare H Jensen
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
| | | | | |
Collapse
|
28
|
Lucas WJ, Groover A, Lichtenberger R, Furuta K, Yadav SR, Helariutta Y, He XQ, Fukuda H, Kang J, Brady SM, Patrick JW, Sperry J, Yoshida A, López-Millán AF, Grusak MA, Kachroo P. The plant vascular system: evolution, development and functions. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2013; 55:294-388. [PMID: 23462277 DOI: 10.1111/jipb.12041] [Citation(s) in RCA: 398] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The emergence of the tracheophyte-based vascular system of land plants had major impacts on the evolution of terrestrial biology, in general, through its role in facilitating the development of plants with increased stature, photosynthetic output, and ability to colonize a greatly expanded range of environmental habitats. Recently, considerable progress has been made in terms of our understanding of the developmental and physiological programs involved in the formation and function of the plant vascular system. In this review, we first examine the evolutionary events that gave rise to the tracheophytes, followed by analysis of the genetic and hormonal networks that cooperate to orchestrate vascular development in the gymnosperms and angiosperms. The two essential functions performed by the vascular system, namely the delivery of resources (water, essential mineral nutrients, sugars and amino acids) to the various plant organs and provision of mechanical support are next discussed. Here, we focus on critical questions relating to structural and physiological properties controlling the delivery of material through the xylem and phloem. Recent discoveries into the role of the vascular system as an effective long-distance communication system are next assessed in terms of the coordination of developmental, physiological and defense-related processes, at the whole-plant level. A concerted effort has been made to integrate all these new findings into a comprehensive picture of the state-of-the-art in the area of plant vascular biology. Finally, areas important for future research are highlighted in terms of their likely contribution both to basic knowledge and applications to primary industry.
Collapse
Affiliation(s)
- William J Lucas
- Department of Plant Biology, College of Biological Sciences, University of California, Davis, CA 95616, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
29
|
Slewinski TL, Zhang C, Turgeon R. Structural and functional heterogeneity in phloem loading and transport. FRONTIERS IN PLANT SCIENCE 2013; 4:244. [PMID: 23847646 PMCID: PMC3701861 DOI: 10.3389/fpls.2013.00244] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Accepted: 06/18/2013] [Indexed: 05/05/2023]
Abstract
The phloem is often regarded as a relatively straightforward transport system composed of loading (collection), long-distance (transport), and unloading (release) zones. While this simple view is necessary and useful in many contexts, it belies the reality, which is that the phloem is inherently complex. At least three types of sieve element-companion cell complexes are found in minor veins of leaves. Individual species may have more than one type, indicating that they employ multiple loading strategies, even in the same vein. Gene expression data in particular point to heterogeneity in sieve element-companion cell complexes of minor veins, perhaps in all flowering plants. Phloem heterogeneity in the transport phloem is also evident in many species based on anatomical, biochemical and gene expression data. In this regard, members of the Cucurbitaceae are especially complex and interesting. We conclude that a hidden world of specialized phloem function awaits discovery.
Collapse
Affiliation(s)
- Thomas L. Slewinski
- *Correspondence: Thomas L. Slewinski and Robert Turgeon, Department of Plant Biology, 262 Plant Science, Cornell University, Ithaca, NY, USA e-mail: ;
| | | | - Robert Turgeon
- *Correspondence: Thomas L. Slewinski and Robert Turgeon, Department of Plant Biology, 262 Plant Science, Cornell University, Ithaca, NY, USA e-mail: ;
| |
Collapse
|
30
|
Dumlao MR, Darehshouri A, Cohu CM, Muller O, Mathias J, Adams WW, Demmig-Adams B. Low temperature acclimation of photosynthetic capacity and leaf morphology in the context of phloem loading type. PHOTOSYNTHESIS RESEARCH 2012; 113:181-9. [PMID: 22791016 DOI: 10.1007/s11120-012-9762-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2012] [Accepted: 06/26/2012] [Indexed: 05/22/2023]
Abstract
Carbon export from leaf mesophyll to sugar-transporting phloem occurs via either an apoplastic (across the cell membrane) or symplastic (through plasmodesmatal cell wall openings) pathway. Herbaceous apoplastic loaders generally exhibit an up-regulation of photosynthetic capacity in response to growth at lower temperature. However, acclimation of photosynthesis to temperature by symplastically loading species, whose geographic distribution is particularly strong in tropical and subtropical areas, has not been characterized. Photosynthetic and leaf anatomical acclimation to lower temperature was explored in two symplastic (Verbascum phoeniceum, Cucurbita pepo) and two apoplastic (Helianthus annuus, Spinacia oleracea) loaders, representing summer- and winter-active life histories for each loading type. Regardless of phloem loading type, the two summer-active species, C. pepo and H. annuus, exhibited neither foliar anatomical nor photosynthetic acclimation when grown under low temperature compared to moderate temperature. In contrast, and again irrespective of phloem loading type, the two winter-active mesophytes, V. phoeniceum and S. oleracea, exhibited both a greater number of palisade cell layers (and thus thicker leaves) and significantly higher maximal capacities of photosynthetic electron transport, as well as, in the case of V. phoeniceum, a greater foliar vein density in response to cool temperatures compared to growth at moderate temperature. It is therefore noteworthy that symplastic phloem loading per se does not prevent acclimation of intrinsic photosynthetic capacity to cooler growth temperatures. Given the vagaries of weather and climate, understanding the basis of plant acclimation to, and tolerance of, low temperature is critical to maintaining and increasing plant productivity for food, fuel, and fiber to meet the growing demands of a burgeoning human population.
Collapse
Affiliation(s)
- Matthew R Dumlao
- Department of Ecology & Evolutionary Biology, University of Colorado, Boulder, CO 80309-0334, USA.
| | | | | | | | | | | | | |
Collapse
|
31
|
Eom JS, Choi SB, Ward JM, Jeon JS. The mechanism of phloem loading in rice (Oryza sativa). Mol Cells 2012; 33:431-8. [PMID: 22453778 PMCID: PMC3887736 DOI: 10.1007/s10059-012-0071-9] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2012] [Accepted: 03/09/2012] [Indexed: 01/03/2023] Open
Abstract
Carbohydrates, mainly sucrose, that are synthesized in source organs are transported to sink organs to support growth and development. Phloem loading of sucrose is a crucial step that drives long-distance transport by elevating hydrostatic pressure in the phloem. Three phloem loading strategies have been identified, two active mechanisms, apoplastic loading via sucrose transporters and symplastic polymer trapping, and one passive mechanism. The first two active loading mechanisms require metabolic energy, carbohydrate is loaded into the phloem against a concentration gradient. The passive process, diffusion, involves equilibration of sucrose and other metabolites between cells through plasmodesmata. Many higher plant species including Arabidopsis utilize the active loading mechanisms to increase carbohydrate in the phloem to higher concentrations than that in mesophyll cells. In contrast, recent data revealed that a large number of plants, especially woody species, load sucrose passively by maintaining a high concentration in mesophyll cells. However, it still remains to be determined how the worldwide important cereal crop, rice, loads sucrose into the phloem in source organs. Based on the literature and our results, we propose a potential strategy of phloem loading in rice. Elucidation of the phloem loading mechanism should improve our understanding of rice development and facilitate its manipulation towards the increase of crop productivity.
Collapse
Affiliation(s)
- Joon-Seob Eom
- Graduate School of Biotechnology and Crop Biotech Institute, Kyung Hee University, Yongin 446-701,
Korea
| | | | | | - Jong-Seong Jeon
- Graduate School of Biotechnology and Crop Biotech Institute, Kyung Hee University, Yongin 446-701,
Korea
| |
Collapse
|
32
|
Liesche J, Schulz A. In vivo quantification of cell coupling in plants with different phloem-loading strategies. PLANT PHYSIOLOGY 2012; 159:355-65. [PMID: 22422939 PMCID: PMC3375970 DOI: 10.1104/pp.112.195115] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2012] [Accepted: 03/09/2012] [Indexed: 05/18/2023]
Abstract
Uptake of photoassimilates into the leaf phloem is the key step in carbon partitioning and phloem transport. Symplasmic and apoplasmic loading strategies have been defined in different plant taxa based on the abundance of plasmodesmata between mesophyll and phloem. For apoplasmic loading to occur, an absence of plasmodesmata is a sufficient but not a necessary criterion, as passage of molecules through plasmodesmata might well be blocked or restricted. Here, we present a noninvasive, whole-plant approach to test symplasmic coupling and quantify the intercellular flux of small molecules using photoactivation microscopy. Quantification of coupling between all cells along the prephloem pathways of the apoplasmic loader Vicia faba and Nicotiana tabacum showed, to our knowledge for the first time in vivo, that small solutes like sucrose can diffuse through plasmodesmata up to the phloem sieve element companion cell complex (SECCC). As expected, the SECCC was found to be symplasmically isolated for small solutes. In contrast, the prephloem pathway of the symplasmic loader Cucurbita maxima was found to be well coupled with the SECCC. Phloem loading in gymnosperms is not well understood, due to a profoundly different leaf anatomy and a scarcity of molecular data compared with angiosperms. A cell-coupling analysis for Pinus sylvestris showed high symplasmic coupling along the entire prephloem pathway, comprising at least seven cell border interfaces between mesophyll and sieve elements. Cell coupling together with measurements of leaf sap osmolality indicate a passive symplasmic loading type. Similarities and differences of this loading type with that of angiosperm trees are discussed.
Collapse
Affiliation(s)
- Johannes Liesche
- Department of Plant Biology and Biotechnology, University of Copenhagen, DK–1871 Frederiksberg C, Denmark
| | - Alexander Schulz
- Department of Plant Biology and Biotechnology, University of Copenhagen, DK–1871 Frederiksberg C, Denmark
| |
Collapse
|
33
|
Leakey ADB, Lau JA. Evolutionary context for understanding and manipulating plant responses to past, present and future atmospheric [CO2]. Philos Trans R Soc Lond B Biol Sci 2012; 367:613-29. [PMID: 22232771 PMCID: PMC3248707 DOI: 10.1098/rstb.2011.0248] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Variation in atmospheric [CO(2)] is a prominent feature of the environmental history over which vascular plants have evolved. Periods of falling and low [CO(2)] in the palaeo-record appear to have created selective pressure for important adaptations in modern plants. Today, rising [CO(2)] is a key component of anthropogenic global environmental change that will impact plants and the ecosystem goods and services they deliver. Currently, there is limited evidence that natural plant populations have evolved in response to contemporary increases in [CO(2)] in ways that increase plant productivity or fitness, and no evidence for incidental breeding of crop varieties to achieve greater yield enhancement from rising [CO(2)]. Evolutionary responses to elevated [CO(2)] have been studied by applying selection in controlled environments, quantitative genetics and trait-based approaches. Findings to date suggest that adaptive changes in plant traits in response to future [CO(2)] will not be consistently observed across species or environments and will not be large in magnitude compared with physiological and ecological responses to future [CO(2)]. This lack of evidence for strong evolutionary effects of elevated [CO(2)] is surprising, given the large effects of elevated [CO(2)] on plant phenotypes. New studies under more stressful, complex environmental conditions associated with climate change may revise this view. Efforts are underway to engineer plants to: (i) overcome the limitations to photosynthesis from today's [CO(2)] and (ii) benefit maximally from future, greater [CO(2)]. Targets range in scale from manipulating the function of a single enzyme (e.g. Rubisco) to adding metabolic pathways from bacteria as well as engineering the structural and functional components necessary for C(4) photosynthesis into C(3) leaves. Successfully improving plant performance will depend on combining the knowledge of the evolutionary context, cellular basis and physiological integration of plant responses to varying [CO(2)].
Collapse
Affiliation(s)
- Andrew D B Leakey
- Department of Plant Biology and Institute for Genomic Biology, University of Illinois, Urbana-Champaign, 1201 W. Gregory Drive, Urbana, IL 61801, USA.
| | | |
Collapse
|
34
|
Fu Q, Cheng L, Guo Y, Turgeon R. Phloem loading strategies and water relations in trees and herbaceous plants. PLANT PHYSIOLOGY 2011; 157:1518-27. [PMID: 21873572 PMCID: PMC3252136 DOI: 10.1104/pp.111.184820] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Accepted: 08/23/2011] [Indexed: 05/18/2023]
Abstract
Most herbaceous plants employ thermodynamically active mechanisms of phloem loading, whereas in many trees, the mechanism is passive, by diffusion. Considering the different water transport characteristics of herbs and trees, we hypothesized that water relations play a role in the adoption of phloem loading strategies. We measured whole-plant hydraulic conductance (K(p)), osmolality, concentrations of polar metabolites, and key inorganic ions in recently mature leaves of 45 dicotyledonous species at midafternoon. Trees, and the few herbs that load passively, have low K(p), high osmolality, and high concentrations of transport sugars and total polar metabolites. In contrast, herbs that actively load sucrose alone have high K(p), low osmolality, and low concentrations of sugars and total polar metabolites. Solute levels are higher in sugar alcohol-transporting species, both herbs and trees, allowing them to operate at lower leaf water potentials. Polar metabolites are largely responsible for leaf osmolality above a baseline level (approximately 300 mm) contributed by ions. The results suggest that trees must offset low K(p) with high concentrations of foliar transport sugars, providing the motivating force for sugar diffusion and rendering active phloem loading unnecessary. In contrast, the high K(p) of most herbaceous plants allows them to lower sugar concentrations in leaves. This reduces inventory costs and significantly increases growth potential but necessitates active phloem loading. Viewed from this perspective, the elevation of hydraulic conductance marks a major milestone in the evolution of the herbaceous habit, not only by facilitating water transport but also by maximizing carbon use efficiency and growth.
Collapse
|
35
|
Vuorinen AL, Kelloniemi J, Valkonen JPT. Why do viruses need phloem for systemic invasion of plants? PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2011; 181:355-63. [PMID: 21889041 DOI: 10.1016/j.plantsci.2011.06.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2010] [Revised: 06/12/2011] [Accepted: 06/15/2011] [Indexed: 05/05/2023]
Abstract
Plant viruses use sieve elements in phloem as the route of long-distance movement and systemic infection in plants. Plants, in turn, deploy RNA silencing, R-gene mediated defence and other mechanisms to prevent phloem transport of viruses. Cell-to-cell movement of viruses from an initially infected leaf to stem and other parts of the plant could be another possibility for systemic invasion, but it is considered to be too slow. This idea is supported by observations made on viruses that are deficient in phloem loading. The leaf abscission zone forming at the base of the petiole may constitute a barrier that prevents viral cell-to-cell movement. The abscission zone and protective layer are difficult to localize in the petiole until the leaf reaches an advanced stage of senescence. Viruses tagged with the green fluorescent protein are helpful for localization and study of the developing abscission zone.
Collapse
Affiliation(s)
- Anssi L Vuorinen
- Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland
| | | | | |
Collapse
|
36
|
Liesche J, Martens HJ, Schulz A. Symplasmic transport and phloem loading in gymnosperm leaves. PROTOPLASMA 2011; 248:181-90. [PMID: 21107620 PMCID: PMC3025105 DOI: 10.1007/s00709-010-0239-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2010] [Accepted: 11/01/2010] [Indexed: 05/18/2023]
Abstract
Despite more than 130 years of research, phloem loading is far from being understood in gymnosperms. In part this is due to the special architecture of their leaves. They differ from angiosperm leaves among others by having a transfusion tissue between bundle sheath and the axial vascular elements. This article reviews the somewhat inaccessible and/or neglected literature and identifies the key points for pre-phloem transport and loading of photoassimilates. The pre-phloem pathway of assimilates is structurally characterized by a high number of plasmodesmata between all cell types starting in the mesophyll and continuing via bundle sheath, transfusion parenchyma, Strasburger cells up to the sieve elements. Occurrence of median cavities and branching indicates that primary plasmodesmata get secondarily modified and multiplied during expansion growth. Only functional tests can elucidate whether this symplasmic pathway is indeed continuous for assimilates, and if phloem loading in gymnosperms is comparable with the symplasmic loading mode in many angiosperm trees. In contrast to angiosperms, the bundle sheath has properties of an endodermis and is equipped with Casparian strips or other wall modifications that form a domain border for any apoplasmic transport. It constitutes a key point of control for nutrient transport, where the opposing flow of mineral nutrients and photoassimilates has to be accommodated in each single cell, bringing to mind the principle of a revolving door. The review lists a number of experiments needed to elucidate the mode of phloem loading in gymnosperms.
Collapse
Affiliation(s)
- Johannes Liesche
- Department of Plant Biology and Biotechnology, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
| | - Helle Juel Martens
- Department of Plant Biology and Biotechnology, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
| | - Alexander Schulz
- Department of Plant Biology and Biotechnology, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
| |
Collapse
|