Habitat Temperature and Precipitation of Arabidopsis thaliana Ecotypes Determine the Response of Foliar Vasculature, Photosynthesis, and Transpiration to Growth Temperature

Spatiotemporal analysis of seasonal trends in land surface temperature within the distribution range of Moringa peregrina (Forssk.) in Southern and Southeastern Iran

Temperature fluctuations and related factors are among the main causes of climate change. Understanding the temporal and spatial variations in temperature can shed light on how species respond to climate change. Plants generally persist in suitable microclimates in response to environmental change; however, examining long-term temperature variations within a species' range can be challenging using field observations. Thermal remote sensing, on the other hand, provides multi-scale time-series data with good coverage and regularity to overcome the challenges associated with field observations in environmental monitoring. Although changes in land surface temperature (LST) affect climate, hydrological processes, land-atmosphere interactions, and ecological activities, this metric has not received much research attention. This study aimed to analyze changes in habitat suitability and microclimatic conditions for Moringa peregrina. Seasonal changes in LST within the distribution range of the species were also investigated. To this aim, mean seasonal LST was computed in Google Earth Engine using the daily MODIS/006/MYD13A2 product from 2003 to 2023. Subsequently, a binary habitat suitability map was created based on the true skill statistic (TSS). The Mann-Kendall test was used to analyze seasonal LST trends. Major trends in LST were quantified based on the z-score, and compatibility with habitat suitability was evaluated via GAP analysis and the Kappa index. Seasonal temperature trends were evaluated by comparing each season with the following season using binary comparison. Landforms at presence points were regarded as microclimates and the sensitivity of microclimates to LST was evaluated using two methods: Principal component analysis (PCA) was used to quantify seasonal LST heterogeneity and the random forest (RF) approach was used to evaluate the effect of environmental parameters on habitat suitability within microclimates. The Kappa index revealed a weak overlapping between suitable / unsuitable habitat and the surfaces affected by the trend of changes. Moreover, the suitable habitat of Moringa peregrina in spring, autumn and winter is spatially overlapped by areas that have shown an increasing LST trend, and the presence points have not experienced an increasing temperature trend only in the summer. The findings show that the analysis of seasonal trends in LST provides insights into the effect of LST on habitat suitability and the condition of vegetation. The current study clearly shows that seasonal changes have had a significant impact on the distribution and habitat suitability of M. peregrina, particularly during summer and winter. Improved habitat suitability and range expansion were observed throughout the year. The study also highlights the role of landforms in regulating temperature. Landforms such as local ridges with minimal temperature fluctuations and regions near the Oman Sea were identified as potential future habitats due to favorable humidity conditions.

Trait variation and performance across varying levels of drought stress in cultivated sunflower (Helianthus annuus L.)

Drought is a major agricultural challenge that is expected to worsen with climate change. A better understanding of drought responses has the potential to inform efforts to breed more tolerant plants. We assessed leaf trait variation and covariation in cultivated sunflower (Helianthus annuus L.) in response to water limitation. Plants were grown under four levels of water availability and assessed for environmentally induced plasticity in leaf stomatal and vein traits as well as biomass (performance indicator), mass fractions, leaf area, leaf mass per area, and chlorophyll content. Overall, biomass declined in response to stress; these changes were accompanied by responses in leaf-level traits including decreased leaf area and stomatal size, and increased stomatal and vein density. The magnitude of trait responses increased with stress severity and relative plasticity of smaller-scale leaf anatomical traits was less than that of larger-scale traits related to construction and growth. Across treatments, where phenotypic plasticity was observed, stomatal density was negatively correlated with stomatal size and positively correlated with minor vein density, but the correlations did not hold up within treatments. Four leaf traits previously shown to reflect major axes of variation in a large sunflower diversity panel under well-watered conditions (i.e. stomatal density, stomatal pore length, vein density, and leaf mass per area) predicted a surprisingly large amount of the variation in biomass across treatments, but trait associations with biomass differed within treatments. Additionally, the importance of these traits in predicting variation in biomass is mediated, at least in part, through leaf size. Our results demonstrate the importance of leaf anatomical traits in mediating drought responses in sunflower, and highlight the role that phenotypic plasticity and multi-trait phenotypes can play in predicting productivity under complex abiotic stresses like drought.

Phloem anatomy predicts berry sugar accumulation across 13 wine-grape cultivars

Introduction

Climate change is impacting the wine industry by accelerating ripening processes due to warming temperatures, especially in areas of significant grape production like California. Increasing temperatures accelerate the rate of sugar accumulation (measured in ⁰Brix) in grapes, however this presents a problem to wine makers as flavor profiles may need more time to develop properly. To alleviate the mismatch between sugar accumulation and flavor compounds, growers may sync vine cultivars with climates that are most amenable to their distinct growing conditions. However, the traits which control such cultivar specific climate adaptation, especially for ⁰Brix accumulation rate, are poorly understood. Recent studies have shown that higher rates of fruit development and sugar accumulation are predicted by larger phloem areas in different organs of the plant.

Methods

Here we test this phloem area hypothesis using a common garden experiment in the Central Valley of Northern California using 18 cultivars of the common grapevine (Vitis vinifera) and assess the grape berry sugar accumulation rates as a function of phloem area in leaf and grape organs.

Results

We find that phloem area in the leaf petiole organ as well as the berry pedicel is a significant predictor of ⁰Brix accumulation rate across 13 cultivars and that grapes from warm climates overall have larger phloem areas than those from hot climates. In contrast, other physiological traits such as photosynthetic assimilation and leaf water potential did not predict berry accumulation rates.

Discussion

As hot climate cultivars have lower phloem areas which would slow down brix accumulation, growers may have inadvertently been selecting this trait to align flavor development with sugar accumulation across the common cultivars tested. This work highlights a new trait that can be easily phenotyped (i.e., petiole phloem area) and be used for growers to match cultivar more accurately with the temperature specific climate conditions of a growing region to obtain satisfactory sugar accumulation and flavor profiles.

Metabolome plasticity in 241 Arabidopsis thaliana accessions reveals evolutionary cold adaptation processes

Acclimation and adaptation of metabolism to a changing environment are key processes for plant survival and reproductive success. In the present study, 241 natural accessions of Arabidopsis (Arabidopsis thaliana) were grown under two different temperature regimes, 16 °C and 6 °C, and growth parameters were recorded, together with metabolite profiles, to investigate the natural genome × environment effects on metabolome variation. The plasticity of metabolism, which was captured by metabolic distance measures, varied considerably between accessions. Both relative growth rates and metabolic distances were predictable by the underlying natural genetic variation of accessions. Applying machine learning methods, climatic variables of the original growth habitats were tested for their predictive power of natural metabolic variation among accessions. We found specifically habitat temperature during the first quarter of the year to be the best predictor of the plasticity of primary metabolism, indicating habitat temperature as the causal driver of evolutionary cold adaptation processes. Analyses of epigenome- and genome-wide associations revealed accession-specific differential DNA-methylation levels as potentially linked to the metabolome and identified FUMARASE2 as strongly associated with cold adaptation in Arabidopsis accessions. These findings were supported by calculations of the biochemical Jacobian matrix based on variance and covariance of metabolomics data, which revealed that growth under low temperatures most substantially affects the accession-specific plasticity of fumarate and sugar metabolism. Our findings indicate that the plasticity of metabolic regulation is predictable from the genome and epigenome and driven evolutionarily by Arabidopsis growth habitats.

Natural variation in photosynthesis and water use efficiency of locally adapted Persian walnut populations under drought stress and recovery

Persian walnut is a drought-sensitive species with considerable genetic variation in the photosynthesis and water use efficiency of its populations, which is largely unexplored. Here, we aimed to elucidate changes in the efficiency of photosynthesis and water content using a diverse panel of 60 walnut families which were submitted to a progressive drought for 24 days, followed by two weeks of re-watering. Severe water-withholding reduced leaf relative water content (RWC) by 20%, net photosynthetic rate (Pn) by 50%, stomatal conductance (gs) by 60%, intercellular CO2 concentration (Ci) by 30%, and transpiration rate (Tr) by 50%, but improved water use efficiency (WUE) by 25%. Severe water-withholding also inhibited photosystem II functionality as indicated by reduced quantum yield of intersystem electron transport (φEo) and transfer of electrons per reaction center (ET0/RC), also enhanced accumulation of QA (VJ) resulted in the reduction of the photosynthetic performance (PIABS) and maximal quantum yield of PSII (FV/FM); while elevated quantum yield of energy dissipation (φDo), energy fluxes for absorption (ABS/RC) and dissipated energy flux (DI0/RC) in walnut families. Cluster analysis classified families into three main groups (tolerant, moderately tolerant, and sensitive), with the tolerant group from dry climates exhibiting lesser alterations in assessed parameters than the other groups. Multivariate analysis of phenotypic data demonstrated that RWC and biophysical parameters related to the chlorophyll fluorescence such as FV/FM, φEo, φDo, PIABS, ABS/RC, ET0/RC, and DI0/RC represent fast, robust and non-destructive biomarkers for walnut performance under drought stress. Finally, phenotype-environment association analysis showed significant correlation of some photosynthetic traits with geoclimatic factors, suggesting a key role of climate and geography in the adaptation of walnut to its habitat conditions.

Genome Editing and Improvement of Abiotic Stress Tolerance in Crop Plants

Genome editing aims to revolutionise plant breeding and could assist in safeguarding the global food supply. The inclusion of a 12-40 bp recognition site makes mega nucleases the first tools utilized for genome editing and first generation gene-editing tools. Zinc finger nucleases (ZFNs) are the second gene-editing technique, and because they create double-stranded breaks, they are more dependable and effective. ZFNs were the original designed nuclease-based approach of genome editing. The Cys2-His2 zinc finger domain's discovery made this technique possible. Clustered regularly interspaced short palindromic repeats (CRISPR) are utilized to improve genetics, boost biomass production, increase nutrient usage efficiency, and develop disease resistance. Plant genomes can be effectively modified using genome-editing technologies to enhance characteristics without introducing foreign DNA into the genome. Next-generation plant breeding will soon be defined by these exact breeding methods. There is abroad promise that genome-edited crops will be essential in the years to come for improving the sustainability and climate-change resilience of food systems. This method also has great potential for enhancing crops' resistance to various abiotic stressors. In this review paper, we summarize the most recent findings about the mechanism of abiotic stress response in crop plants and the use of the CRISPR/Cas mediated gene-editing systems to improve tolerance to stresses including drought, salinity, cold, heat, and heavy metals.

Foliar Phenotypic Plasticity Reflects Adaptation to Environmental Variability

Arabidopsis thaliana ecotypes adapted to native habitats with different daylengths, temperatures, and precipitation were grown experimentally under seven combinations of light intensity and leaf temperature to assess their acclimatory phenotypic plasticity in foliar structure and function. There were no differences among ecotypes when plants developed under moderate conditions of 400 µmol photons m-2 s-1 and 25 °C. However, in response to more extreme light or temperature regimes, ecotypes that evolved in habitats with pronounced differences in either the magnitude of changes in daylength or temperature or in precipitation level exhibited pronounced adjustments in photosynthesis and transpiration, as well as anatomical traits supporting these functions. Specifically, when grown under extremes of light intensity (100 versus 1000 µmol photons m-2 s-1) or temperature (8 °C versus 35 °C), ecotypes from sites with the greatest range of daylengths and temperature over the growing season exhibited the greatest differences in functional and structural features related to photosynthesis (light- and CO2-saturated capacity of oxygen evolution, leaf dry mass per area or thickness, phloem cells per minor vein, and water-use efficiency of CO2 uptake). On the other hand, the ecotype from the habitat with the lowest precipitation showed the greatest plasticity in features related to water transport and loss (vein density, ratio of water to sugar conduits in foliar minor veins, and transpiration rate). Despite these differences, common structure-function relationships existed across all ecotypes and growth conditions, with significant positive, linear correlations (i) between photosynthetic capacity (ranging from 10 to 110 µmol O2 m-2 s-1) and leaf dry mass per area (from 10 to 75 g m-2), leaf thickness (from 170 to 500 µm), and carbohydrate-export infrastructure (from 6 to 14 sieve elements per minor vein, from 2.5 to 8 µm2 cross-sectional area per sieve element, and from 16 to 82 µm2 cross-sectional area of sieve elements per minor vein); (ii) between transpiration rate (from 1 to 17 mmol H2O m-2 s-1) and water-transport infrastructure (from 3.5 to 8 tracheary elements per minor vein, from 13.5 to 28 µm2 cross-sectional area per tracheary element, and from 55 to 200 µm2 cross-sectional area of tracheary elements per minor vein); (iii) between the ratio of transpirational water loss to CO2 fixation (from 0.2 to 0.7 mol H2O to mmol-1 CO2) and the ratio of water to sugar conduits in minor veins (from 0.4 to 1.1 tracheary to sieve elements, from 4 to 6 µm2 cross-sectional area of tracheary to sieve elements, and from 2 to 6 µm2 cross-sectional area of tracheary elements to sieve elements per minor vein); (iv) between sugar conduits and sugar-loading cells; and (v) between water conducting and sugar conducting cells. Additionally, the proportion of water conduits to sugar conduits was greater for all ecotypes grown experimentally under warm-to-hot versus cold temperature. Thus, developmental acclimation to the growth environment included ecotype-dependent foliar structural and functional adjustments resulting in multiple common structural and functional relationships.

Terrestrial and Floating Aquatic Plants Differ in Acclimation to Light Environment

The ability of plants to respond to environmental fluctuations is supported by acclimatory adjustments in plant form and function that may require several days and development of a new leaf. We review adjustments in photosynthetic, photoprotective, and foliar vascular capacity in response to variation in light and temperature in terrestrial plants. The requirement for extensive acclimation to these environmental conditions in terrestrial plants is contrasted with an apparent lesser need for acclimation to different light environments, including rapid light fluctuations, in floating aquatic plants for the duckweed Lemna minor. Relevant features of L. minor include unusually high growth rates and photosynthetic capacities coupled with the ability to produce high levels of photoprotective xanthophylls across a wide range of growth light environments without compromising photosynthetic efficiency. These features also allow L. minor to maximize productivity and avoid problems during an abrupt experimental transfer of low-light-grown plants to high light. The contrasting responses of land plants and floating aquatic plants to the light environment further emphasize the need of land plants to, e.g., experience light fluctuations in their growth environment before they induce acclimatory adjustments that allow them to take full advantage of natural settings with such fluctuations.

Engineering Abiotic Stress Tolerance in Crop Plants through CRISPR Genome Editing

Environmental abiotic stresses challenge food security by depressing crop yields often exceeding 50% of their annual production. Different methods, including conventional as well as genomic-assisted breeding, mutagenesis, and genetic engineering have been utilized to enhance stress resilience in several crop species. Plant breeding has been partly successful in developing crop varieties against abiotic stresses owning to the complex genetics of the traits as well as the narrow genetic base in the germplasm. Irrespective of the fact that genetic engineering can transfer gene(s) from any organism(s), transgenic crops have become controversial mainly due to the potential risk of transgene-outcrossing. Consequently, the cultivation of transgenic crops is banned in certain countries, particularly in European countries. In this scenario, the discovery of the CRISPR tool provides a platform for producing transgene-free genetically edited plants-similar to the mutagenized crops that are not extensively regulated such as genetically modified organisms (GMOs). Thus, the genome-edited plants without a transgene would likely go into the field without any restriction. Here, we focused on the deployment of CRISPR for the successful development of abiotic stress-tolerant crop plants for sustaining crop productivity under changing environments.

Locally adaptive temperature response of vegetative growth in Arabidopsis thaliana

We investigated early vegetative growth of natural Arabidopsis thaliana accessions in cold, nonfreezing temperatures, similar to temperatures these plants naturally encounter in fall at northern latitudes. We found that accessions from northern latitudes produced larger seedlings than accessions from southern latitudes, partly as a result of larger seed size. However, their subsequent vegetative growth when exposed to colder temperatures was slower. The difference was too large to be explained by random population differentiation, and is thus suggestive of local adaptation, a notion that is further supported by substantial transcriptome and metabolome changes in northern accessions. We hypothesize that the reduced growth of northern accessions is an adaptive response and a consequence of reallocating resources toward cold acclimation and winter survival.

Leaf photosynthesis is positively correlated with xylem and phloem areas in leaf veins in rice (Oryza sativa) plants

BACKGROUND AND AIMS

Leaf structure is an important determinant of leaf photosynthesis; however, the impacts of leaf structural traits on gas exchange parameters are still not fully understood. In the present study, 11 rice genotypes were grown in pots to investigate the influence of leaf structural traits on leaf photosynthesis and hydraulic conductance (Kleaf).

METHODS

In this study, leaf photosynthetic rate (A), stomatal conductance (gs), mesophyll conductance and Kleaf were measured. In addition, leaf structural traits including leaf thickness (LT), leaf mass per area and leaf xylem and phloem sizes were also measured to investigate their impacts on rice photosynthesis.

KEY RESULTS

We found that the total area of xylem conduits per major vein (Xmajor), leaf phloem area per minor vein (Pminor) and LT were positively correlated with Kleaf, gs and A. The path analysis suggested that, however, only Pminor had a direct impact on A; Xmajor had an indirect impact on A via gs and Pminor, while LT did not show any direct or indirect impact on A.

CONCLUSION

This study highlighted the importance of manipulations in Xmajor and Pminor, two previously overlooked leaf traits, to improve leaf photosynthesis in rice plants.

Distinct Cold Acclimation of Productivity Traits in Arabidopsis thaliana Ecotypes

Improvement of crop climate resilience will require an understanding of whole-plant adaptation to specific local environments. This review places features of plant form and function related to photosynthetic productivity, as well as associated gene-expression patterns, into the context of the adaptation of Arabidopsis thaliana ecotypes to local environments with different climates in Sweden and Italy. The growth of plants under common cool conditions resulted in a proportionally greater emphasis on the maintenance of photosynthetic activity in the Swedish ecotype. This is compared to a greater emphasis on downregulation of light-harvesting antenna size and upregulation of a host of antioxidant enzymes in the Italian ecotype under these conditions. This differential response is discussed in the context of the climatic patterns of the ecotypes’ native habitats with substantial opportunity for photosynthetic productivity under mild temperatures in Italy but not in Sweden. The Swedish ecotype’s response is likened to pushing forward at full speed with productivity under low temperature versus the Italian ecotype’s response of staying safe from harm (maintaining redox homeostasis) while letting productivity decline when temperatures are transiently cold. It is concluded that either strategy can offer directions for the development of climate-resilient crops for specific locations of cultivation.

Foliar sieve elements: Nexus of the leaf

In this review, a central position of foliar sieve elements in linking leaf structure and function is explored. Results from studies involving plants grown under, and acclimated to, different growth regimes are used to identify significant, linear relationships between features of minor vein sieve elements and those of 1) leaf photosynthetic capacity that drives sugar synthesis, 2) overall leaf structure that serves as the platform for sugar production, 3) phloem components that facilitate the loading of sugars (companion & phloem parenchyma cells), and 4) the tracheary elements that import water to support photosynthesis (and stomatal opening) as well as mass flow of sugars out of the leaf. Despite comprising only a small fraction of physical space within the leaf, sieve elements represent a hub through which multiple functions of the leaf intersect. As the conduits for export of energy-rich carbohydrates, essential mineral nutrients, and information carriers, sieve elements play a central role in fueling and orchestrating development and function of the plant as well as, by extension, of natural and human communities that depend on plants as producers and partners in the global carbon cycle.

Genotype-dependent contribution of CBF transcription factors to long-term acclimation to high light and cool temperature

When grown under cool temperature, winter annuals upregulate photosynthetic capacity as well as freezing tolerance. Here, the role of three cold-induced C-repeat-binding factor (CBF1-3) transcription factors in photosynthetic upregulation and freezing tolerance was examined in two Arabidopsis thaliana ecotypes originating from Italy (IT) or Sweden (SW), and their corresponding CBF1-3-deficient mutant lines it:cbf123 and sw:cbf123. Photosynthetic, morphological and freezing-tolerance phenotypes, as well as gene expression profiles, were characterized in plants grown from the seedling stage under different combinations of light level and temperature. Under high light and cool (HLC) growth temperature, a greater role of CBF1-3 in IT versus SW was evident from both phenotypic and transcriptomic data, especially with respect to photosynthetic upregulation and freezing tolerance of whole plants. Overall, features of SW were consistent with a different approach to HLC acclimation than seen in IT, and an ability of SW to reach the new homeostasis through the involvement of transcriptional controls other than CBF1-3. These results provide tools and direction for further mechanistic analysis of the transcriptional control of approaches to cold acclimation suitable for either persistence through brief cold spells or for maximisation of productivity in environments with continuous low temperatures.

The importance of ecophysiological traits in response of Festuca rubra to changing climate

Knowledge of the ability of plants to respond to climate change via phenotypic plasticity or genetic adaptation in ecophysiological traits and of the link of these traits to fitness is still limited. We studied the clonal grass Festuca rubra from 11 localities representing factorially crossed gradients of temperature and precipitation and cultivated them in growth chambers simulating temperature and moisture regime in the four extreme localities. We measured net photosynthetic rate, F_v /F_m , specific leaf area, osmotic potential and stomatal density and length and tested their relationship to proxies of fitness. We found strong phenotypic plasticity in photosynthetic traits and genetic differentiation in stomatal traits. The effects of temperature and moisture interacted (either as conditions of origin or growth chambers), as were effects of growth and origin. The relationships between the ecophysiological and fitness-related traits were significant but weak. Phenotypic plasticity and genetic differentiation of the species indicate the potential ability of F. rubra to adapt to novel climatic conditions. The most important challenge for the plants seems to be increasing moisture exposing plants to hypoxia. However, the plants have the potential to respond to increased moisture by changes in stomatal size and density and adjustments of osmotic potential. Changes in ecophysiological traits translate into variation in plant fitness, but the selection on the traits is relatively weak and depends on actual conditions. Despite the selection, the plants do not show strong local adaptation and local adaptation is thus likely not restricting species ability to adjust to novel conditions.

Physiological and Molecular Mechanisms of ABA and CaCl2 Regulating Chilling Tolerance of Cucumber Seedlings

Cold stress is a limiting factor to the growth and development of cucumber in the temperate regions; hence, improving the crop's tolerance to low temperature is highly pertinent. The regulation of low-temperature tolerance with exogenous ABA and CaCl₂ was investigated in the cucumber variety Zhongnong 26. Under low-temperature conditions (day/night 12/12 h at 5 °C), seedlings were sprayed with a single application of ABA, CaCl₂, or a combination of both. Our analysis included a calculated chilling injury index, malondialdehyde (MDA) content, relative electrical conductivity, antioxidant enzyme activities (SOD, CAT, and APX), leaf tissue structure, and expression of cold-related genes by transcriptome sequencing. Compared with the water control treatment, the combined ABA + CaCl₂ treatment significantly improved the superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) of the seedlings by 34.47%, 59.66%, and 118.80%, respectively (p < 0.05), and significantly reduced the chilling injury index, relative electrical conductivity, and MDA content, by 89.47%, 62.17%, and 44.55%, respectively (p < 0.05). Transcriptome analysis showed that compared with the water control treatment, 3442 genes were differentially expressed for the combined treatment, 3921 for the ABA treatment, and 1333 for the CaCl₂ treatment. KEGG enrichment analysis for both the ABA and combined ABA + CaCl₂ treatments (as compared to the water control) showed that it mainly involves genes of the photosynthesis pathway and metabolic pathways. Differentially expressed genes following the CaCl₂ treatment were mainly involved in plant hormone signal transduction, plant-pathogen interaction, MAPK signaling pathway-plant, phenylpropanoid biosynthesis, and circadian rhythm-plant. qRT-PCR analysis and RNA-seq results showed a consistent trend in variation of differential gene expression. Overall, this study demonstrated that although all three treatments provided some protection, the combined treatment of ABA (35 mg/L) with CaCl₂ (500 mg/L) afforded the best results. A combined ABA + CaCl₂ treatment can effectively alleviate cold-stress damage to cucumber seedlings by inducing physiological changes in photosynthesis and metabolism, and provides a theoretical basis and technical support for the application of exogenous ABA and CaCl₂ for low-temperature protection of cucumber seedlings.

Photosynthesis and foliar vascular adjustments to growth light intensity in summer annual species with symplastic and apoplastic phloem loading

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.

Effect of low temperature and high humidity stress on physiology of cucumber at different leaf stages

Low temperature (LT) and high humidity (HH) are important environmental factors in greenhouses and plastic tunnels during the cold season, as they hamper plant growth and development. Here, we studied the effect of LT (day/night: 9/5 °C, 25/18 °C as control) and HH (95%, 80% as control) on young cucumber plants at the 2, 4 or 6 leaf stages. LT+HH stress resulted in a decline in shoot, root and total fresh and dry weights, and decreased P_n , g_s , T_r , F_v /F_m , qP, ETR and chlorophyll, and increased MDA, H₂ O₂ , O₂ ^- , NPQ and C_i as compared to the control at the 2 leaf stage. SOD, POD, CAT, APX and GR were upregulated under LT+HH stress as compared to the control at the 6 leaf stage. ABA and JA increased under LT+HH stress as compared to the control at the 6 leaf stage, while IAA and GA decreased under LT+HH stress as compared to the control at the 2 leaf stage. Our results show that LT+HH stress affects young cucumber plant photosynthetic efficiency, PSII activity, antioxidant defence system, ROS and hormone profile. Plants at the 6 leaf stage were more tolerant than at the 2 and 4 leaf stages under stress conditions.

A Tandem Mass Tags (TMTs) labeling approach highlights differences between the shoot proteome of two Arabidopsis thaliana ecotypes, Col-0 and Ws

Arabidopsis has become a powerful model to study morphogenesis, plant growth, development but also plant response to environmental conditions. Over 1000 Arabidopsis genomes are available and show natural genetic variations. Among them, the main reference accessions Wassilewskija (Ws) and Columbia (Col-0), originally growing at contrasted altitudes and temperatures, are widely studied, but data contributing to their molecular phenotyping are still scarce. A global quantitative proteomics approach using isobaric stable isotope labeling (Tandem Mass Tags, TMT) was performed on Ws and Col-0. Plants have been hydroponically grown at 16 h/8 h (light/dark cycle) at 23°C day/19°C night for three weeks. A TMT labeling of the proteins extracted from their shoots has been performed and showed a differential pattern of protein abundance between them. These results have allowed identifying several proteins families possibly involved in the differential responses observed for Ws and Col-0 during plant development and upon environmental changes. In particular, Ws and Col-0 mainly differ in photosynthesis, cell wall-related proteins, plant defense/stress, ROS scavenging enzymes/redox homeostasis and DNA/RNA binding/transcription/translation/protein folding.

The effect of increasing temperature on crop photosynthesis: from enzymes to ecosystems

As global land surface temperature continues to rise and heatwave events increase in frequency, duration, and/or intensity, our key food and fuel cropping systems will likely face increased heat-related stress. A large volume of literature exists on exploring measured and modelled impacts of rising temperature on crop photosynthesis, from enzymatic responses within the leaf up to larger ecosystem-scale responses that reflect seasonal and interannual crop responses to heat. This review discusses (i) how crop photosynthesis changes with temperature at the enzymatic scale within the leaf; (ii) how stomata and plant transport systems are affected by temperature; (iii) what features make a plant susceptible or tolerant to elevated temperature and heat stress; and (iv) how these temperature and heat effects compound at the ecosystem scale to affect crop yields. Throughout the review, we identify current advancements and future research trajectories that are needed to make our cropping systems more resilient to rising temperature and heat stress, which are both projected to occur due to current global fossil fuel emissions.

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

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.

Endopolyploidy is associated with leaf functional traits and climate variation in Arabidopsis thaliana

PREMISE

Endopolyploidy is widespread throughout the tree of life and is especially prevalent in herbaceous angiosperms. Its prevalence in this clade suggests that endopolyploidy may be adaptive, but its functional roles are poorly understood. To address this gap in knowledge, we explored whether endopolyploidy was associated with climatic factors and correlated with phenotypic traits related to growth.

METHODS

We sampled stem and leaf endopolyploidy in 56 geographically separated accessions of Arabidopsis thaliana grown in a common garden to explore species variation and to determine whether this variation was correlated with climatic variables and other plant traits.

RESULTS

Stem endopolyploidy was not associated with climate or other traits. However, leaf endopolyploidy was significantly higher in accessions from drier and colder environments. Moreover, leaf endopolyploidy was positively correlated with apparent chlorophyll content and leaf dry mass.

CONCLUSIONS

Endopolyploidy may have a functional role in the storage of chloroplasts and starch, and it may offer an adaptive avenue of tissue growth in cold and dry environments.

Resistance of Fritillaria imperialis to freezing stress through gene expression, osmotic adjustment and antioxidants

Plant survival in response to freezing stress depends on the efficient activation of tolerance mechanisms. Fritillaria imperialis exposure to freezing stress enhanced signalling molecules Ca²⁺ and H₂O₂ along with overexpression of Ca²⁺ signalling proteins (Ca²⁺ dependent protein kinases, CPK), followed by upregulation of NHX1 (Na⁺/H⁺ antiporter), LEA (late embryogenesis abundant proteins) and P5CS (1-pyrroline-5-carboxylate synthetase). Overexpression of OsCNGC6 was responsible for high accumulation Ca²⁺, Na⁺ and K⁺. The NHX1 gene product transported Na⁺ to vacuoles and increased cytosolic K⁺ content to re-establish ionic homeostasis under stress conditions. The reduced water potential of leaves was due to high accumulation of osmolytes and ions. No changes were observed in relative water content of leaves, which might be correlated with overexpression of the LEA gene, which protects against dehydration. High accumulation of H₂O₂ under freezing stress was responsible for activation of antioxidant systems involving SOD, phenols, anthocyanins, catalase and ascorbate peroxidase. Photosynthesis, suppressed in freezing-stressed plants, returned to normal levels after termination of freezing stress. Taken together, our findings suggest that Fritillaria efficiently tolerated freezing stress through induction of signalling mechanisms and overexpression of cold stress-responsive genes, and prevention of cold-induced water stress, oxidative stress and photosynthetic damage.

Empirical patterns of environmental variation favor adaptive transgenerational plasticity

Effects of parental environment on offspring traits have been well known for decades. Interest in this transgenerational form of phenotypic plasticity has recently surged due to advances in our understanding of its mechanistic basis. Theoretical research has simultaneously advanced by predicting the environmental conditions that should favor the adaptive evolution of transgenerational plasticity. Yet whether such conditions actually exist in nature remains largely unexplored. Here, using long-term climate data, we modeled optimal levels of transgenerational plasticity for an organism with a one-year life cycle at a spatial resolution of 4 km2 across the continental United States. Both annual temperature and precipitation levels were often autocorrelated, but the strength and direction of these autocorrelations varied considerably even among nearby sites. When present, such environmental autocorrelations render offspring environments statistically predictable based on the parental environment, a key condition for the adaptive evolution of transgenerational plasticity. Results of our optimality models were consistent with this prediction: High levels of transgenerational plasticity were favored at sites with strong environmental autocorrelations, and little-to-no transgenerational plasticity was favored at sites with weak or nonexistent autocorrelations. These results are among the first to show that natural patterns of environmental variation favor the evolution of adaptive transgenerational plasticity. Furthermore, these findings suggest that transgenerational plasticity is likely variable in nature, depending on site-specific patterns of environmental variation.

Effects of two centuries of global environmental variation on phenology and physiology of Arabidopsis thaliana

Intraspecific trait variation is caused by genetic and plastic responses to environment. This intraspecific diversity is captured in immense natural history collections, giving us a window into trait variation across continents and through centuries of environmental shifts. Here we tested if hypotheses based on life history and the leaf economics spectrum explain intraspecific trait changes across global spatiotemporal environmental gradients. We measured phenotypes on a 216-year time series of Arabidopsis thaliana accessions from across its native range and applied spatially varying coefficient models to quantify region-specific trends in trait coordination and trait responses to climate gradients. All traits exhibited significant change across space or through time. For example, δ¹⁵ N decreased over time across much of the range and leaf C:N increased, consistent with predictions based on anthropogenic changes in land use and atmosphere. Plants were collected later in the growing season in more recent years in many regions, possibly because populations shifted toward more spring germination and summer flowering as opposed to fall germination and spring flowering. When climate variables were considered, collection dates were earlier in warmer years, while summer rainfall had opposing associations with collection date depending on regions. There was only a modest correlation among traits, indicating a lack of a single life history/physiology axis. Nevertheless, leaf C:N was low for summer- versus spring-collected plants, consistent with a life history-physiology axis from slow-growing winter annuals to fast-growing spring/summer annuals. Regional heterogeneity in phenotype trends indicates complex responses to spatiotemporal environmental gradients potentially due to geographic genetic variation and climate interactions with other aspects of environment. Our study demonstrates how natural history collections can be used to broadly characterize trait responses to environment, revealing heterogeneity in response to anthropogenic change.

Sap Flow Responses to Warming and Fruit Load in Young Olive Trees

Global warming will likely lead to temperature increases in many regions of South America where temperatures are already considered to be high for olive production. Thus, experimental studies are needed to assess how water use in olive trees may be affected by global warming. The objectives of this study were to (i) evaluate the response of olive tree sap flow, stomatal conductance, and xylem anatomy to elevated temperature and (ii) determine whether fruit load may affect the temperature responses. A warming experiment using well-irrigated olive trees (cv. Arbequina) in open-top chambers (OTCs) with two temperature levels was performed from fruit set to the end of fruit growth in two seasons. Temperature levels were a near ambient control (T0) and a treatment 4°C above the control (T+). Trees were in the chambers for either one (2015-2016) or two seasons (2014-2015, 2015-2016) and were evaluated only in the second season when all trees were 3 years old. Whole-tree sap flow on leaf area basis, stomatal conductance, and aspects of xylem anatomy were measured. Sap flow was slightly higher in T+ than T0 trees heated for one season early in fruit development (summer) likely due to the elevated temperature and increase in vapor pressure deficit. Later in fruit development (fall), sap flow was substantially higher in the T+ trees heated for one season. Total vessel number per shoot was greater in the T+ than the T0 trees at this time due to more small-diameter vessels in the T+ trees, but this did not appear to explain the greater sap flow. The T+ trees that were heated for two seasons had less fruit load than the T0 trees due to little flowering. In contrast to trees heated for one season, sap flow was less in T+ than controls late in fruit development the second season, which was likely related to lower fruit load. An independent experiment using untreated trees confirmed that sap flow decreases when fruit load is below a threshold value. The results emphasize that multiple, interacting factors should be considered when predicting warming effects on water use in olive orchards.

Less photoprotection can be good in some genetic and environmental contexts

Antioxidant systems modulate oxidant-based signaling networks and excessive removal of oxidants can prevent beneficial acclimation responses. Evidence from mutant, transgenic, and locally adapted natural plant systems is used to interpret differences in the capacity for antioxidation and formulate hypotheses for future inquiry. We focus on the first line of chloroplast antioxidant defense, pre-emptive thermal dissipation of excess absorbed light (monitored as nonphotochemical fluorescence quenching, NPQ) as well as on tocopherol-based antioxidation. Findings from NPQ-deficient and tocopherol-deficient mutants that exhibited enhanced biomass production and/or enhanced foliar water-transport capacity are reviewed and discussed in the context of the impact of lower levels of antioxidation on plant performance in hot/dry conditions, under cool temperature, and in the presence of biotic stress. The complexity of cellular redox-signaling networks is related to the complexity of environmental and endogenous inputs as well as to the need for intensified training and collaboration in the study of plant-environment interactions across biological sub-disciplines.

Quantification of Leaf Phloem Anatomical Features with Microscopy

Measurements of vein density and foliar minor vein phloem cell numbers, minor vein phloem cell sizes, and transfer cell wall ingrowths provide quantitative proxies for the leaf's capacities to load and export photosynthates. While overall infrastructural capacity for sugar loading and sugar export correlated positively and closely with photosynthetic capacity, the specific targets of the adjustment of minor vein organization varied with phloem-loading mechanism, plant life-cycle characteristics, and environmental growth conditions. Among apoplastic loaders, for which sugar loading into the phloem depends on cell membrane-spanning transport proteins, variation in minor vein density, phloem cell number, and level of cell wall ingrowth (when present) were consistently associated with photosynthetic capacity. Among active symplastic loaders, for which sugar loading into the phloem depends on cytosolic enzymes, variation in vein density and phloem cell size were consistently associated with photosynthetic capacity. All of these anatomical features were also subject to acclimatory adjustment depending on species and environmental conditions, with increased levels of these features supporting higher rates of photosynthesis. We present a procedure for the preparation of leaf tissue for minor vein analysis, using both light and transmission electron microscopy, that facilitates quantification of not only phloem features but also xylem features that provide proxies for foliar water import capacity.

Phenotypic Trait Variation as a Response to Altitude-Related Constraints in Arabidopsis Populations

Natural variations help in identifying genetic mechanisms of morphologically and developmentally complex traits. Mountainous habitats provide an altitudinal gradient where one species encounters different abiotic conditions. We report the study of 341 individuals of Arabidopsis thaliana derived from 30 natural populations not belonging to the 1001 genomes, collected at increasing altitudes, between 200 and 1800 m in the Pyrenees. Class III peroxidases and ribosomal RNA sequences were used as markers to determine the putative genetic relationships among these populations along their altitudinal gradient. Using Bayesian-based statistics and phylogenetic analyses, these Pyrenean populations appear with significant divergence from the other regional accessions from 1001 genome (i.e., from north Spain or south France). Individuals of these populations exhibited varying phenotypic changes, when grown at sub-optimal temperature (22 vs. 15°C). These phenotypic variations under controlled conditions reflected intraspecific morphological variations. This study could bring new information regarding the west European population structure of A. thaliana and its phenotypic variations at different temperatures. The integrative analysis combining genetic, phenotypic variation and environmental datasets is used to analyze the acclimation of population in response to temperature changes. Regarding their geographical proximity and environmental diversity, these populations represent a tool of choice for studying plant response to temperature variation.

HIGHLIGHTS

-Studying the natural diversity of A. thaliana in the Pyrenees mountains helps to understand European population structure and to evaluate the phenotypic trait variation in response to climate change.

CBF-dependent and CBF-independent regulatory pathways contribute to the differences in freezing tolerance and cold-regulated gene expression of two Arabidopsis ecotypes locally adapted to sites in Sweden and Italy

Arabidopsis thaliana (Arabidopsis) increases in freezing tolerance in response to low nonfreezing temperatures, a phenomenon known as cold acclimation. The CBF regulatory pathway, which contributes to cold acclimation, includes three genes—CBF1, CBF2 and CBF3—encoding closely-related transcription factors that regulate the expression of more than 100 genes—the CBF regulon—that impart freezing tolerance. Here we compare the CBF pathways of two Arabidopsis ecotypes collected from sites in Sweden (SW) and Italy (IT). Previous studies showed that the SW ecotype was more freezing tolerant than the IT ecotype and that the IT ecotype had a nonfunctional CBF2 gene. Here we present results establishing that the difference in CBF2 alleles contributes to the difference in freezing tolerance between the two ecotypes. However, other differences in the CBF pathway as well as CBF-independent pathways contribute the large majority of the difference in freezing tolerance between the two ecotypes. The results also provided evidence that most cold-induced CBF regulon genes in both the SW and IT ecotypes are coregulated by CBF-independent pathways. Additional analysis comparing our results with those published by others examining the Col-0 accession resulted in the identification of 44 CBF regulon genes that were conserved among the three accessions suggesting that they likely have important functions in life at low temperature. The comparison further supported the conclusion that the CBF pathway can account for a large portion of the increase in freezing tolerance that occurs with cold acclimation in a given accession, but that CBF-independent pathways can also make a major contribution.

Effect of Cold Stress on Photosynthetic Traits, Carbohydrates, Morphology, and Anatomy in Nine Cultivars of Stevia rebaudiana

Stevia rebaudiana Bertoni is a sweet medicinal herb that is cultivated worldwide. This study aimed to identify the genotypic responses and function of nine cultivars of S. rebaudiana (accession numbers 1-9 from the EUSTAS Stevia Gene Bank) to low temperature. Plants were grown in vitro and incubated under controlled conditions at 5° or 25°C for 1 month. Cold stress significantly decreased the maximum quantum yield of photosystem II (Fv/Fm) in all cultivars, which was more pronounced in cultivars 5, 6, 8, and 9. The efficiency of photosystems I and II (PIABS) also declined in cold-stressed plants and was accompanied by reductions in net photosynthesis (PN), intercellular CO2 (Ci), water use efficiency (WUE), and chlorophyll a, chlorophyll b and carotenoid contents, more so in cultivars 5, 6, 8, and 9. Regardless of the downregulation of photosynthetic capacity, the cold stress increased water-soluble carbohydrates in all cultivars, which was accompanied by an increase in fresh leaf mass and area, more so in cultivars 5, 6, 8, and 9. Furthermore, cold stress increased the stomatal index and density, epidermal cell density, stem diameter, xylem vessel width, phloem tissue width, and number of sclerenchyma in all cultivars. Even though the nine cultivars of S. rebaudiana had lower PSII efficiencies at low temperatures, the increase in carbohydrates and leaf mass suggests that damage to PSII is not responsible for the reduction in its efficiency.

Effects of Foliar Redox Status on Leaf Vascular Organization Suggest Avenues for Cooptimization of Photosynthesis and Heat Tolerance

The interaction of heat stress with internal signaling networks was investigated through Arabidopsisthaliana mutants that were deficient in either tocopherols (vte1 mutant) or non-photochemical fluorescence quenching (NPQ; npq1, npq4, and npq1 npq4 mutants). Leaves of both vte1 and npq1 npq4 mutants that developed at a high temperature exhibited a significantly different leaf vascular organization compared to wild-type Col-0. Both mutants had significantly smaller water conduits (tracheary elements) of the xylem, but the total apparent foliar water-transport capacity and intrinsic photosynthetic capacity were similarly high in mutants and wild-type Col-0. This was accomplished through a combination of more numerous (albeit narrower) water conduits per vein, and a significantly greater vein density in both mutants relative to wild-type Col-0. The similarity of the phenotypes of tocopherol-deficient and NPQ-deficient mutants suggests that leaf vasculature organization is modulated by the foliar redox state. These results are evaluated in the context of interactions between redox-signaling pathways and other key regulators of plant acclimation to growth temperature, such as the C-repeat binding factor (CBF) transcription factors, several of which were upregulated in the antioxidant-deficient mutants. Possibilities for the future manipulation of the interaction between CBF and redox-signaling networks for the purpose of cooptimizing plant productivity and plant tolerance to extreme temperatures are discussed.

Phloem function: a key to understanding and manipulating plant responses to rising atmospheric [CO2]?

Increasing atmospheric carbon dioxide concentration ([CO₂]) directly stimulates photosynthesis and reduces stomatal conductance in C₃ plants. Both of these physiological effects have the potential to alter phloem function at elevated [CO₂]. Recent research has clearly established that photosynthetic capacity is correlated to vascular traits associated with phloem loading and water transport, but the effects of elevated [CO₂] on these relationships are largely unexplored. Plants also employ different strategies for loading sucrose and other sugars into the phloem, and there is potential for species with different phloem loading strategies to respond differently to elevated [CO₂]. Recent research manipulating sucrose transporters and other key enzymes with roles in phloem loading show promise for maximizing crop performance in an elevated [CO₂] world.

Optimization of Photosynthetic Productivity in Contrasting Environments by Regulons Controlling Plant Form and Function

We review the role of a family of transcription factors and their regulons in maintaining high photosynthetic performance across a range of challenging environments with a focus on extreme temperatures and water availability. Specifically, these transcription factors include CBFs (C-repeat binding factors) and DREBs (dehydration-responsive element-binding), with CBF/DREB1 primarily orchestrating cold adaptation and other DREBs serving in heat, drought, and salinity adaptation. The central role of these modulators in plant performance under challenging environments is based on (i) interweaving of these regulators with other key signaling networks (plant hormones and redox signals) as well as (ii) their function in integrating responses across the whole plant, from light-harvesting and sugar-production in the leaf to foliar sugar export and water import and on to the plant's sugar-consuming sinks (growth, storage, and reproduction). The example of Arabidopsisthaliana ecotypes from geographic origins with contrasting climates is used to describe the links between natural genetic variation in CBF transcription factors and the differential acclimation of plant anatomical and functional features needed to support superior photosynthetic performance in contrasting environments. Emphasis is placed on considering different temperature environments (hot versus cold) and light environments (limiting versus high light), on trade-offs between adaptations to contrasting environments, and on plant lines minimizing such trade-offs.

Arabidopsis thaliana Ei-5: Minor Vein Architecture Adjustment Compensates for Low Vein Density in Support of Photosynthesis

An Arabidopsis thaliana accession with naturally low vein density, Eifel-5 (Ei-5), was compared to Columbia-0 (Col-0) with respect to rosette growth, foliar vein architecture, photosynthesis, and transpiration. In addition to having to a lower vein density, Ei-5 grew more slowly, with significantly lower rates of rosette expansion, but had similar capacities for photosynthetic oxygen evolution on a leaf area basis compared to Col-0. The individual foliar minor veins were larger in Ei-5, with a greater number of vascular cells per vein, compared to Col-0. This compensation for low vein density resulted in similar values for the product of vein density × phloem cell number per minor vein in Ei-5 and Col-0, which suggests a similar capacity for foliar sugar export to support similar photosynthetic capacities per unit leaf area. In contrast, the product of vein density × xylem cell number per minor vein was significantly greater in Ei-5 compared to Col-0, and was associated not only with a higher ratio of water-transporting tracheary elements versus sugar-transporting sieve elements but also significantly higher foliar transpiration rates per leaf area in Ei-5. In contrast, previous studies in other systems had reported higher ratios of tracheary to sieve elements and higher transpiration rate to be associated with higher - rather than lower - vein densities. The Ei-5 accession thus further underscores the plasticity of the foliar vasculature by illustrating an example where a higher ratio of tracheary to sieve elements is associated with a lower vein density. Establishment of the Ei-5 accession, with a low vein density but an apparent overcapacity for water flux through the foliar xylem network, may have been facilitated by a higher level of precipitation in its habitat of origin compared to that of the Col-0 accession.

Arabidopsis thaliana Ei-5: Minor Vein Architecture Adjustment Compensates for Low Vein Density in Support of Photosynthesis

An Arabidopsis thaliana accession with naturally low vein density, Eifel-5 (Ei-5), was compared to Columbia-0 (Col-0) with respect to rosette growth, foliar vein architecture, photosynthesis, and transpiration. In addition to having to a lower vein density, Ei-5 grew more slowly, with significantly lower rates of rosette expansion, but had similar capacities for photosynthetic oxygen evolution on a leaf area basis compared to Col-0. The individual foliar minor veins were larger in Ei-5, with a greater number of vascular cells per vein, compared to Col-0. This compensation for low vein density resulted in similar values for the product of vein density × phloem cell number per minor vein in Ei-5 and Col-0, which suggests a similar capacity for foliar sugar export to support similar photosynthetic capacities per unit leaf area. In contrast, the product of vein density × xylem cell number per minor vein was significantly greater in Ei-5 compared to Col-0, and was associated not only with a higher ratio of water-transporting tracheary elements versus sugar-transporting sieve elements but also significantly higher foliar transpiration rates per leaf area in Ei-5. In contrast, previous studies in other systems had reported higher ratios of tracheary to sieve elements and higher transpiration rate to be associated with higher - rather than lower - vein densities. The Ei-5 accession thus further underscores the plasticity of the foliar vasculature by illustrating an example where a higher ratio of tracheary to sieve elements is associated with a lower vein density. Establishment of the Ei-5 accession, with a low vein density but an apparent overcapacity for water flux through the foliar xylem network, may have been facilitated by a higher level of precipitation in its habitat of origin compared to that of the Col-0 accession.

Acclimation of Swedish and Italian ecotypes of Arabidopsis thaliana to light intensity

This study addressed whether ecotypes of Arabidopsis thaliana from Sweden and Italy exhibited differences in foliar acclimation to high versus low growth light intensity, and compared CO₂ uptake under growth conditions with light- and CO₂-saturated intrinsic photosynthetic capacity and leaf morphological and vascular features. Differential responses between ecotypes occurred mainly at the scale of leaf architecture, with thicker leaves with higher intrinsic photosynthetic capacities and chlorophyll contents per leaf area, but no difference in photosynthetic capacity on a chlorophyll basis, in high light-grown leaves of the Swedish versus the Italian ecotype. Greater intrinsic photosynthetic capacity per leaf area in the Swedish ecotype was accompanied by a greater capacity of vascular infrastructure for sugar and water transport, but this was not associated with greater CO₂ uptake rates under growth conditions. The Swedish ecotype with its thick leaves is thus constructed for high intrinsic photosynthetic and vascular flux capacity even under growth chamber conditions that may not permit full utilization of this potential. Conversely, the Swedish ecotype was less tolerant of low growth light intensity than the Italian ecotype, with smaller rosette areas and lesser aboveground biomass accumulation in low light-grown plants. Foliar vein density and stomatal density were both enhanced by high growth light intensity with no significant difference between ecotypes, and the ratio of water to sugar conduits was also similar between the two ecotypes during light acclimation. These findings add to the understanding of the foliar vasculature's role in plant photosynthetic acclimation and adaptation.

Cell wall modifications of two Arabidopsis thaliana ecotypes, Col and Sha, in response to sub-optimal growth conditions: An integrative study

With the global temperature change, plant adaptations are predicted, but little is known about the molecular mechanisms underlying them. Arabidopsis thaliana is a model plant adapted to various environmental conditions, in particular able to develop along an altitudinal gradient. Two ecotypes, Columbia (Col) growing at low altitude, and Shahdara (Sha) growing at 3400m, have been studied at optimal and sub-optimal growth temperature (22°C vs 15°C). Macro- and micro-phenotyping, cell wall monosaccharides analyses, cell wall proteomics, and transcriptomics have been performed in order to accomplish an integrative analysis. The analysis has been focused on cell walls (CWs) which are assumed to play roles in response to environmental changes. At 15°C, both ecotypes presented characteristic morphological traits of low temperature growth acclimation such as reduced rosette diameter, increased number of leaves, modifications of their CW composition and cuticle reinforcement. Altogether, the integrative analysis has allowed identifying several candidate genes/proteins possibly involved in the cell wall modifications observed during the temperature acclimation response.

Three-Dimensional Evaluation on Ecotypic Diversity of Traditional Chinese Medicine: A Case Study of Artemisia annua L

Artemisinin is the first-line drug for anti-malaria recommended by the World Health Organization (WHO). As the sole natural plant source of artemisinin, ecotypes of Artemisia annua L. vary widely in artemisinin content between nations, and China is the main producing area of A. annua. Here we present a three-dimensional evaluation on ecotypic diversity of A. annua from 12 main producing areas in China using high-performance liquid chromatography coupled with evaporative light scattering detection (HPLC-ELSD) method, DNA barcoding and ecological analyses. The results indicated that A. annua exhibited high ecotypic diversity. A. annua grown in the South of the Qinling Mountains-Huaihe River Line had a high artemisinin content, whereas the northern ones were low. Similar pattern was noted in the genetic diversity. The southern A. annua had high intraspecific variation in contrast to the northern A. annua. In terms of ecological analyses, humidity and sunshine time could be the major limiting ecological factors that affect the accumulation of artemisinin. This is the first reported three-dimensional evaluation integrating chemical, molecular and ecological analyses of the ecotypic diversity of A. annua. The work will facilitate exploring the genetic basis of chemical variations and developing strategies for the breeding and cultivation of high quality A. annua.

Environmental regulation of intrinsic photosynthetic capacity: an integrated view

Environmental modulation of photosynthetic capacity is reviewed in the context of its assessment and its regulation, genetic differences among species and ecotypes, and links to plant stress tolerance and productivity. Modulation of intrinsic photosynthetic capacity matches investment in photosynthetic components to opportunity for CO₂ uptake and productivity in specific environments, with exceptionally high rates during particularly narrow windows of opportunity. Response varies among species and ecotypes and should be evaluated on multiple reference bases as well as chloroplast, leaf, and whole plant scales. Photosynthetic capacity, total foliar vascular transport capacity, and plant sink strength are modulated in concert. Switching among alternative target sinks and alternative foliar vascular architectures may provide avenues for co-optimization of productivity and stress tolerance.

Light, temperature and tocopherol status influence foliar vascular anatomy and leaf function in Arabidopsis thaliana

This study addressed whether the winter annual Arabidopsis thaliana can adjust foliar phloem and xylem anatomy both differentially and in parallel. In plants acclimated to hot vs cool temperature, foliar minor vein xylem-to-phloem ratio was greater, whereas xylem and phloem responded concomitantly to growth light intensity. Across all growth conditions, xylem anatomy correlated with transpiration rate, while phloem anatomy correlated with photosynthetic capacity for two plant lines (wild-type Col-0 and tocopherol-deficient vte1 mutant) irrespective of tocopherol status. A high foliar vein density (VD) was associated with greater numbers and cross-sectional areas of both xylem and phloem cells per vein as well as higher rates of both photosynthesis and transpiration under high vs low light intensities. Under hot vs cool temperature, high foliar VD was associated with a higher xylem-to-phloem ratio and greater relative rates of transpiration to photosynthesis. Tocopherol status affected development of foliar vasculature as dependent on growth environment. The most notable impact of tocopherol deficiency was seen under hot growth temperature, where the vte1 mutant exhibited greater numbers of tracheary elements (TEs) per vein, a greater ratio of TEs to sieve elements, with smaller individual sizes of TEs, and resulting similar total areas of TEs per vein and transpiration rates compared with Col-0 wild-type. These findings illustrate the plasticity of foliar vascular anatomy acclimation to growth environment resulting from independent adjustments of the vasculature's components.