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Gilman IS, Smith JAC, Holtum JAM, Sage RF, Silvera K, Winter K, Edwards EJ. The CAM lineages of planet Earth. ANNALS OF BOTANY 2023; 132:627-654. [PMID: 37698538 PMCID: PMC10799995 DOI: 10.1093/aob/mcad135] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Revised: 01/09/2023] [Accepted: 09/11/2023] [Indexed: 09/13/2023]
Abstract
BACKGROUND AND SCOPE The growth of experimental studies of crassulacean acid metabolism (CAM) in diverse plant clades, coupled with recent advances in molecular systematics, presents an opportunity to re-assess the phylogenetic distribution and diversity of species capable of CAM. It has been more than two decades since the last comprehensive lists of CAM taxa were published, and an updated survey of the occurrence and distribution of CAM taxa is needed to facilitate and guide future CAM research. We aimed to survey the phylogenetic distribution of these taxa, their diverse morphology, physiology and ecology, and the likely number of evolutionary origins of CAM based on currently known lineages. RESULTS AND CONCLUSIONS We found direct evidence (in the form of experimental or field observations of gas exchange, day-night fluctuations in organic acids, carbon isotope ratios and enzymatic activity) for CAM in 370 genera of vascular plants, representing 38 families. Further assumptions about the frequency of CAM species in CAM clades and the distribution of CAM in the Cactaceae and Crassulaceae bring the currently estimated number of CAM-capable species to nearly 7 % of all vascular plants. The phylogenetic distribution of these taxa suggests a minimum of 66 independent origins of CAM in vascular plants, possibly with dozens more. To achieve further insight into CAM origins, there is a need for more extensive and systematic surveys of previously unstudied lineages, particularly in living material to identify low-level CAM activity, and for denser sampling to increase phylogenetic resolution in CAM-evolving clades. This should allow further progress in understanding the functional significance of this pathway by integration with studies on the evolution and genomics of CAM in its many forms.
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Affiliation(s)
- Ian S Gilman
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA
| | | | - Joseph A M Holtum
- College of Science and Engineering, James Cook University, Townsville, Queensland, Australia
| | - Rowan F Sage
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Katia Silvera
- Smithsonian Tropical Research Institute, Balboa, Ancón, Panama
- Department of Botany & Plant Sciences, University of California, Riverside, CA, USA
| | - Klaus Winter
- Smithsonian Tropical Research Institute, Balboa, Ancón, Panama
| | - Erika J Edwards
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA
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Holtum JAM. The diverse diaspora of CAM: a pole-to-pole sketch. ANNALS OF BOTANY 2023; 132:597-625. [PMID: 37303205 PMCID: PMC10800000 DOI: 10.1093/aob/mcad067] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 12/13/2022] [Accepted: 06/09/2023] [Indexed: 06/13/2023]
Abstract
BACKGROUND Crassulacean acid metabolism (CAM) photosynthesis is a successful adaptation that has evolved often in angiosperms, gymnosperms, ferns and lycophytes. Present in ~5 % of vascular plants, the CAM diaspora includes all continents apart from Antarctica. Species with CAM inhabit most landscapes colonized by vascular plants, from the Arctic Circle to Tierra del Fuego, from below sea level to 4800 m a.s.l., from rainforests to deserts. They have colonized terrestrial, epiphytic, lithophytic, palustrine and aquatic systems, developing perennial, annual or geophyte strategies that can be structurally arborescent, shrub, forb, cladode, epiphyte, vine or leafless with photosynthetic roots. CAM can enhance survival by conserving water, trapping carbon, reducing carbon loss and/or via photoprotection. SCOPE This review assesses the phylogenetic diversity and historical biogeography of selected lineages with CAM, i.e. ferns, gymnosperms and eumagnoliids, Orchidaceae, Bromeliaceae, Crassulaceae, Euphorbiaceae, Aizoaceae, Portulacineae (Montiaceae, Basellaceae, Halophytaceae, Didiereaceae, Talinaceae, Portulacaceae, Anacampserotaceae and Cactaceae) and aquatics. CONCLUSIONS Most extant CAM lineages diversified after the Oligocene/Miocene, as the planet dried and CO2 concentrations dropped. Radiations exploited changing ecological landscapes, including Andean emergence, Panamanian Isthmus closure, Sundaland emergence and submergence, changing climates and desertification. Evidence remains sparse for or against theories that CAM biochemistry tends to evolve before pronounced changes in anatomy and that CAM tends to be a culminating xerophytic trait. In perennial taxa, any form of CAM can occur depending upon the lineage and the habitat, although facultative CAM appears uncommon in epiphytes. CAM annuals lack strong CAM. In CAM annuals, C3 + CAM predominates, and inducible or facultative CAM is common.
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Affiliation(s)
- Joseph A M Holtum
- College of Science and Engineering, James Cook University, Townsville, QLD4811, Australia
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Mok D, Leung A, Searles P, Sage TL, Sage RF. CAM photosynthesis in Bulnesia retama (Zygophyllaceae), a non-succulent desert shrub from South America. ANNALS OF BOTANY 2023; 132:655-670. [PMID: 37625031 PMCID: PMC10799978 DOI: 10.1093/aob/mcad114] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Revised: 07/19/2023] [Accepted: 08/23/2023] [Indexed: 08/27/2023]
Abstract
BACKGROUND AND AIMS Bulnesia retama is a drought-deciduous, xerophytic shrub from arid landscapes of South America. In a survey of carbon isotope ratios (δ13C) in specimens from the field, B. retama exhibited less negative values, indicative of CAM or C4 photosynthesis. Here, we investigate whether B. retama is a C4 or CAM plant. METHODS Gas-exchange responses to intercellular CO2, diurnal gas-exchange profiles, δ13C and dawn vs. afternoon titratable acidity were measured on leaves and stems of watered and droughted B. retama plants. Leaf and stem cross-sections were imaged to determine whether the tissues exhibited succulent CAM or C4 Kranz anatomy. KEY RESULTS Field-collected stems and fruits of B. retama exhibited δ13C between -16 and -19 ‰. Plants grown in a glasshouse from field-collected seeds had leaf δ13C values near -31 ‰ and stem δ13C values near -28 ‰. The CO2 response of photosynthesis showed that leaves and stems used C3 photosynthesis during the day, while curvature in the nocturnal response of net CO2 assimilation rate (A) in all stems, coupled with slightly positive rates of A at night, indicated modest CAM function. C4 photosynthesis was absent. Succulence was absent in all tissues, although stems exhibited tight packing of the cortical chlorenchyma in a CAM-like manner. Tissue titratable acidity increased at night in droughted stems. CONCLUSIONS Bulnesia retama is a weak to modest C3 + CAM plant. This is the first report of CAM in the Zygophyllaceae and the first showing that non-succulent, xerophytic shrubs use CAM. CAM alone in B. retama was too limited to explain less negative δ13C in field-collected plants, but combined with effects of low stomatal and mesophyll conductance it could raise δ13C to observed values between -16 and -19 ‰. Modest CAM activity, particularly during severe drought, could enable B. retama to persist in arid habitats of South America.
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Affiliation(s)
- Daniel Mok
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Wilcocks Street, Toronto, Ontario M5R3C6, Canada
| | - Arthur Leung
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Wilcocks Street, Toronto, Ontario M5R3C6, Canada
| | - Peter Searles
- Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja (CRILAR-CONICET), Entre Ríos y Mendoza s/n, Anillaco (5301), La Rioja, Argentina
| | - Tammy L Sage
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Wilcocks Street, Toronto, Ontario M5R3C6, Canada
| | - Rowan F Sage
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Wilcocks Street, Toronto, Ontario M5R3C6, Canada
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Hu Z, He Z, Li Y, Wang Q, Yi P, Yang J, Yang C, Borovskii G, Cheng X, Hu R, Zhang W. Transcriptomic and metabolic regulatory network characterization of drought responses in tobacco. FRONTIERS IN PLANT SCIENCE 2023; 13:1067076. [PMID: 36743571 PMCID: PMC9891310 DOI: 10.3389/fpls.2022.1067076] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Accepted: 11/30/2022] [Indexed: 06/18/2023]
Abstract
Drought stress usually causes huge economic losses for tobacco industries. Drought stress exhibits multifaceted impacts on tobacco systems through inducing changes at different levels, such as physiological and chemical changes, changes of gene transcription and metabolic changes. Understanding how plants respond and adapt to drought stress helps generate engineered plants with enhanced drought resistance. In this study, we conducted multiple time point-related physiological, biochemical,transcriptomic and metabolic assays using K326 and its derived mutant 28 (M28) with contrasting drought tolerance. Through integrative analyses of transcriptome and metabolome,we observed dramatic changes of gene expression and metabolic profiles between M28 and K326 before and after drought treatment. we found that some of DEGs function as key enzymes responsible for ABA biosynthesis and metabolic pathway, thereby mitigating impairment of drought stress through ABA signaling dependent pathways. Four DEGs were involved in nitrogen metabolism, leading to synthesis of glutamate (Glu) starting from NO-3 /NO-2 that serves as an indicator for stress responses. Importantly, through regulatory network analyses, we detected several drought induced TFs that regulate expression of genes responsible for ABA biosynthesis through network, indicating direct and indirect involvement of TFs in drought responses in tobacco. Thus, our study sheds some mechanistic insights into how plant responding to drought stress through transcriptomic and metabolic changes in tobacco. It also provides some key TF or non-TF gene candidates for engineering manipulation for breeding new tobacco varieties with enhanced drought tolerance.
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Affiliation(s)
- Zhengrong Hu
- Hunan Tobacco Research Institute, Changsha, Hunan, China
| | - Zexue He
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Collaborative Innovation Center for Modern Crop Production (JCIC-MCP), Collaborative Innovation Center for Modern Crop Production Co-Sponsored by Province and Ministry (CIC-MCP), Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Yangyang Li
- Hunan Tobacco Research Institute, Changsha, Hunan, China
| | - Qing Wang
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Collaborative Innovation Center for Modern Crop Production (JCIC-MCP), Collaborative Innovation Center for Modern Crop Production Co-Sponsored by Province and Ministry (CIC-MCP), Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Pengfei Yi
- Hu'nan Tobacco Company Changde Company, Changde, Hunan, China
| | - Jiashuo Yang
- Hunan Tobacco Research Institute, Changsha, Hunan, China
| | - Chenkai Yang
- College of Agronomy, Hunan Agricultural University, Changsha, Hunan, China
| | - Gennadii Borovskii
- Siberian Institute of Plant Physiology and Biochemistry Siberian Branch of Russian Academy of Sciences (SB RAS) Irkutsk, Lermontova, Russia
| | - Xuejiao Cheng
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Collaborative Innovation Center for Modern Crop Production (JCIC-MCP), Collaborative Innovation Center for Modern Crop Production Co-Sponsored by Province and Ministry (CIC-MCP), Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Risheng Hu
- Hunan Tobacco Research Institute, Changsha, Hunan, China
| | - Wenli Zhang
- State Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Collaborative Innovation Center for Modern Crop Production (JCIC-MCP), Collaborative Innovation Center for Modern Crop Production Co-Sponsored by Province and Ministry (CIC-MCP), Nanjing Agricultural University, Nanjing, Jiangsu, China
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Young SNR, Dunning LT, Liu H, Stevens CJ, Lundgren MR. C4 trees have a broader niche than their close C3 relatives. JOURNAL OF EXPERIMENTAL BOTANY 2022; 73:3189-3204. [PMID: 35293994 PMCID: PMC9126736 DOI: 10.1093/jxb/erac113] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Accepted: 03/12/2022] [Indexed: 06/14/2023]
Abstract
Previous studies have demonstrated the ecological sorting of herbaceous C3 and C4 species along gradients of precipitation and temperature: C4 herbaceous species typically occupy drier and warmer environments than their C3 relatives. However, it is unclear if this pattern holds true for C4 tree species, which are unique to Euphorbiaceae and found only on the Hawaiian Islands. Here, we combine occurrence data with local environmental and soil datasets to, for the first time, distinguish the ecological factors associated with photosynthetic diversification in the tree life form. These data are presented within a phylogenetic framework. We show that C3 and C4 trees inhabit similar environments, but that C4 photosynthesis expands the ecological niche in trees relative to that of C3 tree species. In particular, when compared with C3 trees, C4 trees moved into higher elevation habitats with characteristically sparse vegetation (and thus greater sunlight) and cooler temperatures, a pattern which contrasts with that of herbaceous species. Understanding the relationship between C4 photosynthesis and ecological niche in tree species has implications for establishing how C4 photosynthesis has, in this rare instance, evolved in trees, and whether this unique combination of traits could be exploited from an engineering perspective.
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Affiliation(s)
- Sophie N R Young
- Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
| | - Luke T Dunning
- Ecology and Evolutionary Biology, School of Biosciences, University of Sheffield, Sheffield S10 2TN, UK
| | - Hui Liu
- Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Xingke Road 723, Guangzhou 510650, China
| | - Carly J Stevens
- Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
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Winter K, Garcia M, Virgo A, Ceballos J, Holtum JAM. Does the C 4 plant Trianthema portulacastrum (Aizoaceae) exhibit weakly expressed crassulacean acid metabolism (CAM)? FUNCTIONAL PLANT BIOLOGY : FPB 2021; 48:655-665. [PMID: 33213694 DOI: 10.1071/fp20247] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Accepted: 10/06/2020] [Indexed: 06/11/2023]
Abstract
We examined whether crassulacean acid metabolism (CAM) is present in Trianthema portulacastrum L. (Aizoaceae), a pantropical, salt-tolerant C4 annual herb with atriplicoid-type Kranz anatomy in leaves but not in stems. The leaves of T. portulacastrum are slightly succulent and the stems are fleshy, similar to some species of Portulaca, the only genus known in which C4 and CAM co-occur. Low- level nocturnal acidification typical of weakly expressed, predominantly constitutive CAM was measured in plants grown for their entire life-cycle in an outdoor raised garden box. Acidification was greater in stems than in leaves. Plants showed net CO2 uptake only during the light irrespective of soil water availability. However, nocturnal traces of CO2 exchange exhibited curved kinetics of reduced CO2 loss during the middle of the night consistent with low-level CAM. Trianthema becomes the second genus of vascular land plants in which C4 and features of CAM have been demonstrated to co-occur in the same plant and the first C4 plant with CAM-type acidification described for the Aizoaceae. Traditionally the stems of herbs are not sampled in screening studies. Small herbs with mildly succulent leaves and fleshy stems might be a numerically significant component of CAM biodiversity.
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Affiliation(s)
- Klaus Winter
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panama; and Corresponding author.
| | - Milton Garcia
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panama
| | - Aurelio Virgo
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panama
| | - Jorge Ceballos
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panama
| | - Joseph A M Holtum
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panama; and College of Science and Engineering, James Cook University, Townsville, Qld 4811, Australia
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Winter K, Garcia M, Virgo A, Holtum JAM. Operating at the very low end of the crassulacean acid metabolism spectrum: Sesuvium portulacastrum (Aizoaceae). JOURNAL OF EXPERIMENTAL BOTANY 2019; 70:6561-6570. [PMID: 30535159 PMCID: PMC6883264 DOI: 10.1093/jxb/ery431] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Accepted: 11/30/2018] [Indexed: 05/31/2023]
Abstract
Demonstration of crassulacean acid metabolism (CAM) in species with low usage of this system relative to C3-photosynthetic CO2 assimilation can be challenging experimentally but provides crucial information on the early steps of CAM evolution. Here, weakly expressed CAM was detected in the well-known pantropical coastal, leaf-succulent herb Sesuvium portulacastrum, demonstrating that CAM is present in the Sesuvioideae, the only sub-family of the Aizoaceae in which it had not yet been shown conclusively. In outdoor plots in Panama, leaves and stems of S. portulacastrum consistently exhibited a small degree of nocturnal acidification which, in leaves, increased during the dry season. In potted plants, nocturnal acidification was mainly facultative, as levels of acidification increased in a reversible manner following the imposition of short-term water-stress. In drought-stressed plants, nocturnal net CO2 exchange approached the CO2-compensation point, consistent with low rates of CO2 dark fixation sufficient to eliminate respiratory carbon loss. Detection of low-level CAM in S. portulacastrum adds to the growing number of species that cannot be considered C3 plants sensu stricto, although they obtain CO2 principally via the C3 pathway. Knowledge about the presence/absence of low-level CAM is critical when assessing trajectories of CAM evolution in lineages. The genus Sesuvium is of particular interest because it also contains C4 species.
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Affiliation(s)
- Klaus Winter
- Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panama
| | - Milton Garcia
- Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panama
| | - Aurelio Virgo
- Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panama
| | - Joseph A M Holtum
- Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panama
- Centre for Tropical Biodiversity and Climate Change, College of Science and Engineering, James Cook University, Townsville, Queensland, Australia
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Functional Anatomical Traits of the Photosynthetic Organs of Plants with Crassulacean Acid Metabolism. THE LEAF: A PLATFORM FOR PERFORMING PHOTOSYNTHESIS 2018. [DOI: 10.1007/978-3-319-93594-2_10] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Holtum JAM, Hancock LP, Edwards EJ, Winter K. Facultative CAM photosynthesis (crassulacean acid metabolism) in four species of Calandrinia, ephemeral succulents of arid Australia. PHOTOSYNTHESIS RESEARCH 2017; 134:17-25. [PMID: 28871459 DOI: 10.1007/s11120-017-0359-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 02/14/2017] [Indexed: 06/07/2023]
Abstract
Crassulacean acid metabolism (CAM) was demonstrated in four small endemic Australian terrestrial succulents from the genus Calandrinia (Montiaceae) viz. C. creethiae, C. pentavalvis, C. quadrivalvis and C. reticulata. CAM was substantiated by measurements of CO2 gas-exchange and nocturnal acidification. In all species, the expression of CAM was overwhelmingly facultative in that nocturnal H+ accumulation was greatest in droughted plants and zero, or close to zero, in plants that were well-watered, including plants that had been droughted and were subsequently rewatered, i.e. the inducible component was proven to be reversible. Gas-exchange measurements complemented the determinations of acidity. In all species, net CO2 uptake was restricted to the light in well-watered plants, and cessation of watering was followed by a progressive reduction of CO2 uptake in the light and a reduction in nocturnal CO2 efflux. In C. creethiae, C. pentavalvis and C. reticulata net CO2 assimilation was eventually observed in the dark, whereas in C. quadrivalvis nocturnal CO2 exchange approached the compensation point but did not transition to net CO2 gain. Following rewatering, all species returned to their original well-watered CO2 exchange pattern of net CO2 uptake restricted solely to the light. In addition to facultative CAM, C. quadrivalvis and C. reticulata exhibited an extremely small constitutive CAM component as demonstrated by the nocturnal accumulation in well-watered plants of small amounts of acidity and by the curved pattern of the nocturnal course of CO2 efflux. It is suggested that low-level CAM and facultative CAM are more common within the Australian succulent flora, and perhaps the world succulent flora, than has been previously assumed.
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Affiliation(s)
- Joseph A M Holtum
- College of Science and Engineering, James Cook University, Townsville, QLD, 4811, Australia.
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panama.
| | - Lillian P Hancock
- Department of Ecology and Evolutionary Biology, Brown University, Box G-W, Providence, RI, 02912, USA
| | - Erika J Edwards
- Department of Ecology and Evolutionary Biology, Brown University, Box G-W, Providence, RI, 02912, USA
| | - Klaus Winter
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panama
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Holtum JAM, Hancock LP, Edwards EJ, Winter K. Optional use of CAM photosynthesis in two C 4 species, Portulaca cyclophylla and Portulaca digyna. JOURNAL OF PLANT PHYSIOLOGY 2017; 214:91-96. [PMID: 28511087 DOI: 10.1016/j.jplph.2017.01.010] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Revised: 01/28/2017] [Accepted: 01/30/2017] [Indexed: 06/07/2023]
Abstract
Low levels of crassulacean acid metabolism (CAM) are demonstrated in two species with C4 photosynthesis, Portulaca cyclophylla and P. digyna. The expression of CAM in P. cyclophylla and P. digyna is facultative, i.e. optional. Well-watered plants did not accumulate acid at night and exhibited gas-exchange patterns consistent with C4 photosynthesis. CAM-type nocturnal acidification was reversible in that it was induced following drought and lost when droughted plants were rewatered. In P. cyclophylla, droughting was accompanied by a small but discernible net uptake of CO2 during the dark, whereas in P. digyna, net CO2 exchange at night approached the CO2 compensation point but did not transition beyond it. This report brings the number of known C4 species with a capacity for expressing CAM to six. All are species of Portulaca. The observation of CAM in P. cyclophylla and P. digyna is the first for species in the opposite-leaved (OL) Portulacelloid-anatomy lineage of Portulaca and for the Australian clade therein. The other four species are within the alternate-leaved (AL) lineage, in the Atriploid-anatomy Oleracea and the Pilosoid-anatomy Pilosa clades. Studies of the evolutionary origins of C4 and CAM in Portulaca will benefit from a more wide-range survey of CAM across its species, particularly in the C3-C4 intermediate-containing Cryptopetala clade.
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Affiliation(s)
- Joseph A M Holtum
- Centre for Tropical Biodiversity and Climate Change, College of Science and Engineering, James Cook University, Townsville 4811, Queensland, Australia; Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Panama.
| | - Lillian P Hancock
- Department of Ecology and Evolutionary Biology, Brown University, Box G-W, Providence RI 02912, USA.
| | - Erika J Edwards
- Department of Ecology and Evolutionary Biology, Brown University, Box G-W, Providence RI 02912, USA.
| | - Klaus Winter
- Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Panama.
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