Stomatal Pore Research Articles

Transcriptomic dynamics of ABA response in Brassica napus guard cells

Drought has a significant, negative impact on crop production; and these effects are poised to increase with climate change. Plants acclimate to drought and water stress through diverse physiological responses, primarily mediated by the hormone abscisic acid (ABA). Because plants lose the majority of their water through stomatal pores on aerial surfaces of plants, stomatal closure is one of the rapid responses mediated by ABA to reduce transpirational water loss. The dynamic changes in the transcriptome of stomatal guard cells in response to ABA have been investigated in the model plant Arabidopsis thaliana. However, guard cell transcriptomes have not been analyzed in agronomically valuable crops such as a major oilseed crop, rapeseed. In this study, we investigated the dynamics of ABA-regulated transcriptomes in stomatal guard cells of Brassica napus and conducted comparison analysis with the transcriptomes of A. thaliana. We discovered changes in gene expression indicating alterations in a host of physiological processes, including stomatal movement, metabolic reprogramming, and light responses. Our results suggest the existence of both immediate and delayed responses to ABA in Brassica guard cells. Furthermore, the transcription factors and regulatory networks mediating these responses are compared to those identified in Arabidopsis. Our results imply the continuing evolution of ABA responses in Brassica since its divergence from a common ancestor, involving both protein-coding and non-coding nucleotide sequences. Together, our results will provide a basis for developing strategies for molecular manipulation of drought tolerance in crop plants.

Gaining or cutting SLAC: the evolution of plant guard cell signalling pathways.

The evolution of adjustable stomatal pores, enabling CO2 acquisition, was one of the most significant events in the development of life on land. Here, we investigate how the guard cell signalling pathways that regulate stomatal movements evolved. We compare fern and angiosperm guard cell transcriptomes and physiological responses, and examine the functionality of ion channels from diverse plant species. We find that, despite conserved expression in guard cells, fern anion channels from the SLAC/SLAH family are not activated by the same abscisic acid (ABA) pathways that provoke stomatal closure in angiosperms. Accordingly, we find an insensitivity of fern stomata to ABA. Moreover, our analysis points to a complex evolutionary history, featuring multiple gains and/or losses of SLAC activation mechanisms, as these channels were recruited to a role in stomatal closure. Our results show that the guard cells of flowering and nonflowering plants share similar core features, with lineage-specific and ecological niche-related adaptations, likely underlying differences in behaviour.

Guard cells count the number of unitary cytosolic Ca2+ signals to regulate stomatal dynamics.

Transient stimulus-specific increases in the cytosolic Ca2+ concentration ("calcium signatures") of guard cells have been proposed to regulate the opening and closure of stomatal pores on plant leaves. However, the mechanism by which these Ca2+ signatures are generated and translated into stomatal movement is still largely unresolved. We used a light-gated, Ca2+-permeable variant of ChannelRhodopsin 2 (ChR2-XXM2.0) that was stimulated by tailored light pulses to investigate this phenomenon. We found that activation of the ChR2-XXM2.0 channel provoked characteristic increases in the cytosolic concentration of Ca2+. We also demonstrated that the endoplasmic reticulum (ER) was involved in the generation of these calcium signatures. Using ChR2-XXM2.0 technology, we showed that transient increases in Ca2+ activated S-type anion channels and determined the extent and speed of stomatal closure with their number and frequency. Our data reveal that guard cells are capable of counting Ca2+ transients in order to optimize stomatal aperture in the prevailing environmental conditions.

Foliar epidermal micro-morphology of selected brinjal varieties: A study on leaf surface characteristics

Studies on the leaf epidermal morphological characteristics were conducted on the three varieties of brinjal (Solanum melongena L.) belonging to the family Solanaceae. The varieties used in the study were Bhavani Gold, Purple Round and Haritha. Fresh mature brinjal leaves were randomly selected from the three experimental genotypes, and the foliar epidermal features were studied by using light microscopy and SEM imaging. Measurements were taken with an ocular and stage micrometer using 10X and 40X magnifications. The photographs were taken from mounted slides. The stomatal count and each measurement represent the average of ten readings. The upper and lower epidermal surfaces of leaf were studied for stomatal features including, stomatal distribution, stomatal type, stomatal index, stomatal pore length, stomatal pore width, guard cell length, guard cell width, subsidiary cell length and width, epidermal cell type, epidermal cell length and width, trichome type, trichome length and width. Amphistomatous, anisocytic, and with more stomata on the lower epidermal surface than the upper epidermal surface were present in all leaf varieties. On the leaves, the abaxial stomatal index ranged from 68.19 mm-2 (Bhavani Gold) to 56.67 mm-2 (Purple Round) to 58.8 mm-2 (Haritha). While on the adaxial surface, it varied from 59.67 mm-2 (Bhavani Gold), 53.46 mm-2 (Purple Round) and 56.67 mm-2 (Haritha). The three varieties of this study exhibited similarities in the pattern of epidermal cell on the adaxial and abaxial surfaces and were irregular in shape. Among the three varieties epidermal cell become irregular in outline and trichomes were present on both leaf surfaces. It becomes stellate, non-glandular, glandular and 8-12 in number. The highest trichome length was obtained in Bhavani Gold (63 μm) followed by Haritha (57.5 μm) and Purple Round (43 μm) on the upper epidermis. On the lower epidermal region maximum length was obtained in Bhavani Gold (65.5 μm) followed by Haritha (53 μm) and Purple Round (44 μm).

Photomorphogenesis and Photosynthetic Trait Changes in Melon Seedlings Responding to Red and Blue Light

Red and blue light have significant effects on plant growth; however, most of the current studies have focused on common horticultural crops such as cucumber and tomato, and there are fewer studies on how red and blue light affect the growth of melon seedlings. Therefore, in this study, we used melon (Cucumis melo L.) as the experimental material to investigate the effects of red and blue light ratios on the photomorphogenesis and photosynthesis of melon seedlings. Five red and blue light ratios were set at a fixed light intensity 200 μmol·m−2·s−1, including R:B = 1:9, R:B = 3:7, R:B = 1:1, R:B = 7:3, and R:B = 9:1. The results showed that with the increase in red light ratios, melon seedling height, stem diameter, total leaf area and stomatal pore size of melon seedlings increased, while the upper epidermis, palisade tissue, spongy tissue, leaf thickness, and stomatal density showed a decreasing trend. Under the R:B = 7:3 treatment, melon seedlings were optimized in all morphological indexes and had higher photosynthetic efficiency; these results indicated that the growth of melon seedlings could be regulated by adjusting the ratio of red to blue light, thus promoting the morphogenesis of melon seedlings.

Lamiales epidermal dynamics: Unveiling antimicrobial resilience in a structural symphony.

This research on Lamiales epidermal anatomy not only provides in-depth understanding of their structural traits but also highlights the significance of uncovering the inherent antimicrobial resilience embedded within these plants. Such insights hold promise for advancing natural product-based approaches in medicine, potentially contributing to the development of novel antimicrobial agents inspired by Lamiales unique biological defense mechanisms. Scanning microscopic tools were utilized to conduct foliar epidermal anatomy of nine species that belong to seven genera and four families within the Lamiales order, Plantaginaceae, Scrophulariaceae, Verbenaceae, and Lamiaceae. This approach aimed to gather both qualitative and quantitative data, facilitating the assessment of taxonomic microanatomical significance. The shape of epidermal cells and their anticlinal walls; number of epidermal cells, stomata, and trichomes; type of stomata and trichomes; length and width of epidermal cells, trichomes, stomatal pore, guard cells, and subsidiary cells; and stomatal index were determined statistically. Most of the species examined were amphistomatous and showed extensive array of trichomes diversity. The exploration of Lamiales epidermal micromorphology and their antimicrobial potential were significant for their implications in multidisciplinary fields. The pharmacological research to utilize sustainable agricultural practices prompts avenues to strengths of Lamiales order for the development of novel antimicrobial solutions and ecological benefits. RESEARCH HIGHLIGHTS: Diverse trichome morphometry reveals a wide array of trichome structures across Lamiales species. Epidermal microscopic architecture variability of epidermal cell shapes and sizes signifies the interspecies variability. Secondary metabolite localization within microanatomical structures elucidates potential hotspots for antimicrobial compound production.

Photosynthate, heavy metals contents, biochemical characteristics and anatomical responses in Telfairia occidentalis. and Amaranthus hybridus collected within akure metropolis

Heavy metals in soils pose a potential threat to the environment and can cause significant damage to human and animal health. This study aimed to assess heavy metal concentrations, photosynthate levels, biochemical characteristics, and anatomical responses in Telfairia occidentalis and Amaranthus hybridus collected within Akure metropolis, Ondo State, Nigeria. Fresh vegetable samples were randomly collected from four fertilized farmlands (denoted as A, B, C, and D) within the Akure metropolis. Heavy metal concentrations in the vegetable samples were determined using an Atomic Absorption Spectrophotometer (AAS). The pigment content (Chlorophyll a and b) of the vegetables was measured, while the activities of Catalase (CAT), Superoxide Dismutase (SOD), and reduced glutathione (GSH) were estimated. Stomatal architecture and epithelial cell structure were also analyzed. Results indicated that CAT (7.45 ± 0.36 U/mg protein) and SOD (6.21 ± 0.28 U/mg protein) activities, as well as GSH content (4.63 ± 0.12 µmol/g tissue), were highest in vegetables collected from farm A, showing statistically significant differences compared to other farms (p < 0.05). The concentrations of heavy metals in the leaves of vegetables collected from all farms were below the standard limits recommended by WHO/FAO, with the exception of Lead (Pb), which was significantly higher than the permissible limit in farm B (2.14 ± 0.09 mg/kg; p < 0.05). Chlorophyll content was significantly reduced in both vegetables compared to the control (chlorophyll a: 2.56 ± 0.21 mg/g tissue in T. occidentalis and 2.03 ± 0.19 mg/g tissue in A. hybridus; p < 0.05). This reduction in chlorophyll content correlated with the elevated levels of Pb in farm B (r = -0.87, p < 0.05). The stomatal architecture analysis revealed significant alterations in stomatal density and pore size in both vegetables from contaminated farms. These findings suggest the need for biomonitoring programs to control heavy metal accumulation in Nigerian farmlands, as elevated levels of Pb can disrupt the physiological and biochemical processes of vegetables, posing potential health risks to consumers.

Stomatal patterning is differently regulated in adaxial and abaxial epidermis in Arabidopsis.

Stomatal pores in leaves mediate CO2 uptake into the plant and water loss via transpiration. Most plants are hypostomatous with stomata present only in the lower leaf surface (abaxial epidermis). Many herbs, including the model plant Arabidopsis thaliana, have substantial numbers of stomata also on the upper (adaxial) leaf surface. Studies of stomatal development have mostly focused on abaxial stomata and very little is known of adaxial stomatal formation. We addressed the role of leaf number in determination of stomatal density and stomatal ratio, and studied adaxial and abaxial stomatal patterns in mutants deficient in known abaxial stomatal development regulators. We found that stomatal density in some genetic backgrounds varies between different fully expanded leaves and recommend using defined leaves for analyses of stomatal patterning. Our results indicate that stomatal development is at least partly independently regulated in adaxial and abaxial epidermis, as i) plants deficient in ABA biosynthesis and perception have increased stomatal ratios, ii) the epf1epf2, tmm and sdd1 mutants have reduced stomatal ratios, iii) erl2 mutants have increased adaxial but not abaxial stomatal index, and iv) stomatal precursors preferentially occur in abaxial epidermis. Further studies of adaxial stomata can reveal new insights into stomatal form and function.

Integrated Effects of Soil Moisture on Wheat Hydraulic Properties and Stomatal Regulation.

The development of water-saving management relies on understanding the physiological response of crops to soil drought. The coordinated regulation of hydraulics and stomatal conductance in plant water relations has steadily received attention. However, research focusing on grain crops, such as winter wheat, remains limited. In this study, three soil water supply treatments, including high (H), moderate (M), and low (L) soil water contents, were conducted with potted winter wheat. Leaf water potential (Ψleaf), leaf hydraulic conductance (Kleaf), and stomatal conductance (gs), as well as leaf biochemical parameters and stomatal traits were measured. Results showed that, compared to H, predawn leaf water potential (ΨPD) significantly reduced by 48.10% and 47.91%, midday leaf water potential (ΨMD) reduced by 40.71% and 43.20%, Kleaf reduced by 64.80% and 65.61%, and gs reduced by 21.20% and 43.41%, respectively, under M and L conditions. Although gs showed a significant difference between M and L, Ψleaf and Kleaf did not show significant differences between these treatments. The maximum carboxylation rate (Vcmax) and maximum electron transfer rate (Jmax) under L significantly decreased by 23.11% and 28.10%, stomatal density (SD) and stomatal pore area index (SPI) under L on the abaxial side increased by 59.80% and 52.30%, respectively, compared to H. The leaf water potential at 50% hydraulic conduction loss (P50) under L was not significantly reduced. The gs was positively correlated with ΨMD and Kleaf, but it was negatively correlated with abscisic acid (ABA) and SD. A threshold relationship between gs and Kleaf was observed, with rapid and linear reduction in gs occurring only when Kleaf fell below 8.70 mmol m-2 s-1 MPa-1. Our findings demonstrate that wheat leaves adapt stomatal regulation strategies from anisohydric to isohydric in response to reduced soil water content. These results enrich the theory of trade-offs between the carbon assimilation and hydraulic safety in crops and also provide a theoretical basis for water management practices based on stomatal regulation strategies under varying soil water conditions.

Enhanced root system architecture in oilseed rape transformed with Rhizobium rhizogenes

Transformation of plants using wild strains of agrobacteria is termed natural transformation and is not covered by GMO legislation in e.g. European Union and Japan. In the current study, offspring lines (A11 and B3) of Rhizobium rhizogenes naturally transformed oilseed rape (Brassica napus) were randomly selected to characterize the morphological traits, and analyze the implications of such morphological changes on plant drought resilience. It was found that the introduction of Ri-genes altered the biomass partitioning to above- and under-ground parts of oilseed rape plants. Compared to the wild type (WT), the A11 and B3 lines exhibited 1.2–4.0 folds lower leaf and stem dry weight, leaf area and plant height, but had 1.3–5.8 folds greater root dry weight, root length and root surface area, resulting in a significantly enhanced root: shoot dry mass ratio and root surface area: leaf area ratio. In addition, the introduction of Ri-genes conferred reduced stomatal pore aperture and increased stomatal density in the B3 line, and increased leaf thickness in A11 line, which could benefit plant drought resilience. Finally, the modulations in morphological traits as a consequence of transformation with Ri-genes are discussed concerning resilience in water-limited conditions. These findings reveal the potential of natural transformation with R. rhizogenes for drought-targeted breeding in crops.

Low relative air humidity and increased stomatal density independently hamper growth in young Arabidopsis.

Stomatal pores in plant leaves mediate CO2 uptake for photosynthesis and water loss via transpiration. Altered stomatal density can affect plant photosynthetic capacity, water use efficiency, and growth, potentially providing either benefits or drawbacks depending on the environment. Here we explore, at different air humidity regimes, gas exchange, stomatal anatomy, and growth of Arabidopsis lines designed to combine increased stomatal density (epf1, epf2) with high stomatal sensitivity (ht1-2, cyp707a1/a3). We show that the stomatal density and sensitivity traits combine as expected: higher stomatal density increases stomatal conductance, whereas the effect is smaller in the high stomatal sensitivity mutant backgrounds than in the epf1epf2 double mutant. Growth under low air humidity increases plant stomatal ratio with relatively more stomata allocated to the adaxial epidermis. Low relative air humidity and high stomatal density both independently impair plant growth. Higher evaporative demand did not punish increased stomatal density, nor did inherently low stomatal conductance provide any protection against low relative humidity. We propose that the detrimental effects of high stomatal density on plant growth at a young age are related to the cost of producing stomata; future experiments need to test if high stomatal densities might pay off in later life stages.

Taxonomical implications of foliar epidermal anatomy of Impatiens L. species (Balsaminaceae) in the Nilgiris, Southern Western Ghats, India

The foliar epidermal anatomy of 22 Impatiens species from the family Balsaminaceae was studied. The study intended to determine whether the micromorphological characteristics of the genus Impatiens were taxonomically significant and would aid in the precise identification of the species. The qualitative and quantitative traits as well as diagnostic characteristics were identified using a Light microscope. Variations were observed in both adaxial and abaxial leaf micromorphological characters like the shape of the epidermal and guard cells, anticlinal wall pattern, lobes per cell, stomatal pore, distribution of stomata, type of stomata and the presence and nature of trichomes. Anomocyic stomata exclusively occurred in all the studied Impatiens species. Stomata were present on both the surface of I. scabriscula B. Heyne ex Walland I. balsamina L., while in rest of the studied species stomata restricted on abaxial surface. An elliptical pore is the dominant type of stomatal pore among the investigated impatiens taxa. Uniseriate multicellular trichomes were observed (I. tenella B.Heyne ex Hook., I. fruticosa Lesch ex DC, I. gardeneriana Wight, I. minor (DC.) Bennet, I. rufescens Benth ex Wight & Arn). For accurate species delineation and identification in the genus Impatiens, taxonomic keys have been developed based on foliar micromorphology.

Fighting for Survival at the Stomatal Gate.

Stomata serve as the battleground between plants and plant pathogens. Plants can perceive pathogens, inducing closure of the stomatal pore, while pathogens can overcome this immune response with their phytotoxins and elicitors. In this review, we summarize new discoveries in stomata-pathogen interactions. Recent studies have shown that stomatal movement continues to occur in a close-open-close-open pattern during bacterium infection, bringing a new understanding of stomatal immunity. Furthermore, the canonical pattern-triggered immunity pathway and ion channel activities seem to be common to plant-pathogen interactions outside of the well-studied Arabidopsis-Pseudomonas pathosystem. These developments can be useful to aid in the goal of crop improvement. New technologies to study intact leaves and advances in available omics data sets provide new methods for understanding the fight at the stomatal gate. Future studies should aim to further investigate the defense-growth trade-off in relation to stomatal immunity, as little is known at this time.

Biochemical versus stomatal acclimation of dynamic photosynthetic gas exchange to elevated CO2 in three horticultural species with contrasting stomatal morphology.

Understanding photosynthetic acclimation to elevated CO2 (eCO2) is important for predicting plant physiology and optimizing management decisions under global climate change, but is underexplored in important horticultural crops. We grew three crops differing in stomatal density-namely chrysanthemum, tomato, and cucumber-at near-ambient CO2 (450 μmol mol-1) and eCO2 (900 μmol mol-1) for 6 weeks. Steady-state and dynamic photosynthetic and stomatal conductance (gs) responses were quantified by gas exchange measurements. Opening and closure of individual stomata were imaged in situ, using a novel custom-made microscope. The three crop species acclimated to eCO2 with very different strategies: Cucumber (with the highest stomatal density) acclimated to eCO2 mostly via dynamic gs responses, whereas chrysanthemum (with the lowest stomatal density) acclimated to eCO2 mostly via photosynthetic biochemistry. Tomato exhibited acclimation in both photosynthesis and gs kinetics. eCO2 acclimation in individual stomatal pore movement increased rates of pore aperture changes in chrysanthemum, but such acclimation responses resulted in no changes in gs responses. Although eCO2 acclimation occurred in all three crops, photosynthesis under fluctuating irradiance was hardly affected. Our study stresses the importance of quantifying eCO2 acclimatory responses at different integration levels to understand photosynthetic performance under future eCO2 environments.

Nanoparticle Uptake and Bioaccumulation in Pisum sativum L. (Green Pea) Analyzed via Dark-Field Microscopy, Infrared Spectroscopy, and Principal Component Analysis Combined with Machine Learning

The green pea (Pisum sativum L.) is an economically, nutritionally, and culturally important legume. It is a crop that is subject to various investigations due to its popularity with the development of various protocols in different topics, except for nano-biotechnological studies. This work was carried out to evaluate the uptake, distribution, translocation, and bioaccumulation of the single-walled carbon nanotubes (CNTs) and gold nanoparticles (AuNPs) within the economically important plant Pisum sativum morphologically and anatomically with a dark-field microscopy system. Data were analyzed for morphological parameters such as stem, tendril, root length, number, shape, width-length of the stipules, and root-stem-stipule. Our results proved the stimulation for growth and anatomical parameters such as CNTs aggregates and AuNPs particles at paranchyma, cortex, spongia cells, starch formation and accumulation in lenticels, stoma cells, and stomatal pores. In this study, we compared the utilization of the entire available Attenuated Total Reflectance—Fourier Transform Infrared Spectroscopy (ATR-FTIR) spectral range (525–4000 cm−1) for conducting principal component analysis (PCA) without excluding any specific spectral wavenumbers with the spectral range chosen based on larger PCA loadings. The results demonstrate that for both chosen spectral ranges of the PCA score plots, utilizing only the first three principal components (PCs), we effectively visually separated three groups: (1) plants treated with Au NPs, (2) plants treated with CNTs, and (3) control plants without nanoparticle treatment using ATR-FTIR spectral data from combined samples of root, stem, and leaves from the Pisum sativum plant. Our investigation shows that green pea, a species of the Fabaceae family, is low-cost, fast, and non-toxic and requires an environmentally safe process in the area of nanotechnology in bio-application regarding the green synthesis of nanoparticles; it is a step for green mining, phytoremediation, delivering drugs, and biomolecules. Our findings show that green pea and the Fabaceae family have more advantages for the biological synthesis of C-Au nanoparticles and guide soil health, agricultural development, pharmaceuticals, drug delivery science, and other types of medicinal investigations with a new approach, while a lot of economic plants in the Fabaceae family will be available for the green synthesis of more NPs with single and rapid protocols and will be a popular family in nano-biotechnological studies in the next few decades.

Analysis of Intra- Cultivar Heterogeneity in Dashehari Mango (Mangifera Indica L.) by Using Scanning Electron Microscopy

The present study aimed at estimating intra-cultivar heterogeneity in Dashehari cultivar of mango (Mangifera indica L.) by using Scanning Electron Microscopy (SEM). Forty-five trees of 25-30 years old, from 15 orchards in Malihabad and Mall blocks of district Lucknow, Uttar Pradesh were selected for study which revealed a significant variation in all stomatal characteristics. Phenotypic and Genotypic coefficient of variation (PCV and GCV, respectively) values for these parameters were very close, indicating that they were controlled at genetic level and were independent of environmental effect. Highest phenotypic (41.59) and genotypic (38.27) coefficient of variation, and Genetic advance as percent of mean (GAM) (149.41 %) were recorded for stomatal pore size (width) while highest (97.50) heritability (h2) and genetic advance (20.86) were observed for stomatal density. Dendrogram clusters of the Dashehari population under study, prepared based on stomatal observations, divided into two main clusters which further divided into sub-clusters. The study on stomatal characters is fully facilitated by SEM and hence, it is suggested that SEM may be a useful tool for identification of intra-varietal variability of Dashehari mango for further crop improvement programme. Bangladesh J. Bot. 53(2): 391-399, 2024 (June)

Stomatal CO2 responses at sub- and above-ambient CO2 levels employ different pathways in Arabidopsis.

Stomatal pores that control plant CO2 uptake and water loss affect global carbon and water cycles. In the era of increasing atmospheric CO2 levels and vapor pressure deficit (VPD), it is essential to understand how these stimuli affect stomatal behavior. Whether stomatal responses to sub-ambient and above-ambient CO2 levels are governed by the same regulators and depend on VPD remains unknown. We studied stomatal conductance responses in Arabidopsis (Arabidopsis thaliana) stomatal signaling mutants under conditions where CO2 levels were either increased from sub-ambient to ambient (400 ppm) or from ambient to above-ambient levels under normal or elevated VPD. We found that guard cell signaling components involved in CO2-induced stomatal closure have different roles in the sub-ambient and above-ambient CO2 levels. The CO2-specific regulators prominently affected sub-ambient CO2 responses, whereas the lack of guard cell slow-type anion channel SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1) more strongly affected the speed of above-ambient CO2-induced stomatal closure. Elevated VPD caused lower stomatal conductance in all studied genotypes and CO2 transitions, as well as faster CO2-responsiveness in some studied genotypes and CO2 transitions. Our results highlight the importance of experimental setups in interpreting stomatal CO2-responsiveness, as stomatal movements under different CO2 concentration ranges are controlled by distinct mechanisms. Elevated CO2 and VPD responses may also interact. Hence, multi-factor treatments are needed to understand how plants integrate different environmental signals and translate them into stomatal responses.

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.

Micromorphological and Chemical Characterization of Drimys winteri Leaf Surfaces: The Secondary Alcohols Forming Epicuticular Wax Crystals Are Accompanied by Alkanediol, Alkanetriol and Ketol Derivatives.

The cuticle is a hydrophobic coating of most aerial plant surfaces crucial for limiting non-stomatal water loss. Plant cuticles consist of the lipid polyester cutin and associated waxes with compositions varying widely between plant species and organs. Here, we aimed to provide a comparative analysis of the dark-glossy adaxial and pale-glaucous abaxial sides of Drimys winteri (Winteraceae) leaves. Scanning electron microscopy showed nanotubular wax crystals lining the entire abaxial side of the leaf (including stomatal pores), while the adaxial side had patches of mixed platelet/tubule crystals and smooth areas between them. Consecutive treatments for wax removal and cutin depolymerization revealed that the waxes were deposited on a cutin network with micron-scale cavities across the entire abaxial surface including the stomata pores, and on a microscopically smooth cutin surface on the adaxial side of the leaf. Gas chromatography coupled to mass spectrometry and flame ionization detection showed that the wax mixtures on both sides of the leaf were complex mixtures of very-long-chain compounds dominated by the secondary alcohol nonacosan-10-ol and alkanediols with one hydroxyl on C-10. It is therefore very likely that the characteristic tubular wax crystals of both leaf sides are formed by these alcohols and diols. Further secondary alcohols and alkanediols, as well as ketols and alkanetriols with one functional group on C-10, were identified based on mass spectral fragmentation patterns. The similarities between all these mid-chain-functionalized compounds suggest that they are derived from nonacosan-10-ol via regio-specific hydroxylation reactions, likely catalyzed by three P450-dependent monooxygenases with different regio-specificities.

Architecture and functions of stomatal cell walls in eudicots and grasses.

Like all plant cells, the guard cells of stomatal complexes are encased in cell walls that are composed of diverse, interacting networks of polysaccharide polymers. The properties of these cell walls underpin the dynamic deformations that occur in guard cells as they expand and contract to drive the opening and closing of the stomatal pore, the regulation of which is crucial for photosynthesis and water transport in plants. Our understanding of how cell wall mechanics are influenced by the nanoscale assembly of cell wall polymers in guard cell walls, how this architecture changes over stomatal development, maturation and ageing and how the cell walls of stomatal guard cells might be tuned to optimize stomatal responses to dynamic environmental stimuli is still in its infancy. In this review, we discuss advances in our ability to probe experimentally and to model the structure and dynamics of guard cell walls quantitatively across a range of plant species, highlighting new ideas and exciting opportunities for further research into these actively moving plant cells.