Stomatal Structure Research Articles

Method for fast staining and obtaining high-magnification and high-resolution cell images of Nicotiana benthamiana.

The online version contains supplementary material available at 10.1007/s12298-021-00931-5.

Stomatal Structure in Symphyotrichum Nees Species as an Additional Index of Invasiveness

The study was aimed on a comparison of morphometric traits of the stomatal apparatus in cultivated Symphyotrichum Nees species to evaluate the adaptive capacity of these alien taxa. The study included eleven Symphyotrichum species from the collection of the Botanical Garden of Padua (Italy): S. novi-belgii, S. novae-angliae, S. ciliolatum, S. laeve, S. lateriflorum, S. puniceum, S. × salignum, S. × versicolor, S. chilense, S. cordifolium, and S. tradescantii. For these species, original data on 21 quantitative morphometric characteristics of the stomatal apparatus are presented. The species were divided into three groups according to the index of relative transpiration area (RTA). High RTA values (12–14%) were observed in S. novae-angliae, S. novi-belgii, and S. × salignum; medium RTA values (3–7%) were typical of S. lateriflorum, S. ciliolatum, S. laeve, S. × versicolor, and S. puniceum; finally, low RTA values (0.2–2.0%) were revealed in S. chilense, S. cordifolium, and S. tradescantii. As in the previous study of the genus Solidago, a positive correlation was observed between the RTA and the invasiveness of alien species. A hypothesis was proposed that a high RTA value indicates a greater adaptability of alien species and, along with other traits, can be used to predict the further expansion of their secondary range and possibility of their transformation into invasive species.

English

The present study investigated the role of inoculation with Nitrobien biofertilizer (N-Bio, Azospirillum and azotobacter spp.) on the response of maize plants to cadmium-toxicity (applied as 2 and 10 mM CdSO4). Cd-stress caused a significant reduction in the fresh and dry biomass of leaves and roots as well as a marked disturbance in the anatomical features of roots and stomatal structure and behavior. Cd-stress significantly depressed the total photosynthetic pigments, photochemical efficiency of PS II, total carbohydrates, and proteins content. Furthermore, increasing Cd level prompted oxidative stress measured in terms of malondialdehyde and H2O2 contents in maize plants. Application of N-Bio improved these attributes in Cd-stressed maize plants. Moreover, NO3- uptake and its assimilating enzymes (nitrate reductase, NR; glutamine synthase, GS; and, glutamate dehydrogenase GDH) were significantly increased in N-Bio-pretreated Cd-stressed plants than Cd- stressed ones and that was associated with a decrease of NH4+ content. N-Bio pretreatment also stimulated the accumulation of amino acids and markedly increased endogenous phytohormone content (IAA, GA3) of Cd-stressed maize plants. These results revealed the potentiating effect of N-Bio pretreatment in regulating Cd-induced damages in maize plants. © 2021 Friends Science Publishers

Leaf anatomical adaptation of eighteen mangrove plant species from the Sundarbans in Bangladesh

Investigation on leaf anatomical adaptation of 18 mangrove plant species was carried out. Among the 18 species 13 were dorsiventral and five were isobilateral type. All the species had special stomatal structure and variable cuticle layer to minimize transpiration. Most of the species had succulent leaves with leaf thickness ranging from around 232 to 1363 μm. As an indication of salt secretion, both glandular and non-glandular trichomes were observed in several species. Although presence of single to multilayered hypodermis might effectively function as water storage tissue, several studied mangrove plant species e.g. Cynometra ramiflora L., Phoenix paludosa Roxb., Pongamea pinnata (L.) Pierre, Sonneratia apetala Buch. - Ham., S. caseolaris (L.) Engl. and Xylocarpus moluccensis (Lamk.) M. Roem. showed complete absence of hypodermis. This might be due to moderate saline condition. In addition, marked terminal tracheids in mesophyll tissue of a number of species might help with capillary water storage within the leaf. To enhance mechanical support several species were found to develop considerable amount of diverse sclereids within the mesophyll tissue and surrounding vascular bundle. Although maximum anatomical adaptations are common for plants growing in saline habitat it may be suggested that these features were differentially developed in plants specifically grown in mesohaline zone.

KARAKTERISASI STOMATA DAUN PEGAGAN (Centella asiatica (L.) Urban.) PADA KETINGGIAN WILAYAH BERBEDA DI PULAU AMBON

The purpose of this study was to determine the anatomical structure of pegagan leaves through stomata characterization at several different locations on Ambon Island. Survey method was used in this research. The sample was taken in nine villages were spread from lowlands to the highlands on Ambon Island. The procedure of semi-permanent preparations was done by whole mount method. Stomata characterization was done towards the stomata number, stomata density, and stomata index. The collected data were analyzed by descriptive analysis and performed in the form of table or figure. the research result shows that leaf with high stomata number was tend to high in stomata density and stomata index. Based on this research result, it could be conclude that there are no difference of stomatal structure of Pegagan leaves in all location were sample collected. The difference has shown by numbers, density, and stomatal index. The highest Numbers, density and stomatal index shown on Pegagan leaves in lowland, and the lowest that shown in this research on Pegagan leaves in highland

Foliar micro-morphology: a promising tool to improve survival percentage of tissue culture raised plantlets with special reference to in vitro propagation of Vitex negundo L.

The in vitro induced anomalies during micropropagation affect acclimatization process of the regenerants, which influence the survival success of tissue culture raised plantlets. The comparative foliar micro-morphological analysis of in vitro developed; ex vitro adapted and field transferred plantlets could help in understanding the acclimatization of micropropagated plants. An enhanced shoot regeneration system for Vitex negundo L. was developed through axillary shoot regeneration and ex vitro rooting methods in present study. Murashige and Skoog’s medium (MS) incorporated with 1.5 mg L−1 6-benzylaminopurine (BAP) was recorded optimum for shoot regeneration from nodal segments. The shoots were further amplified (34.5 ± 0.21 shoots per culture vessel with 11.9 ± 0.10 cm average length) on full strength MS medium containing 0.5 mg L−1 BAP and 0.25 mg L−1 indole-3 acetic acid (IAA). The in vitro regenerated shoots were rooted under laboratory conditions (on half strength of MS medium incorporated with 1.0 mg L−1 IBA) as well as in greenhouse (ex vitro) when the shoots were treated with 300 mg L−1 IBA for 5 min. The hardened plantlets were successfully transferred to the field. The micro-morphological changes were observed in stomatal structure, index, veins and trichome density on the leaves developed in each stage of propagation of V. negundo. In vitro induced micro-morphological anomalies reduced stability of plant health and survival percentage which ultimately lead to the reduction in number of plantlets. The keen foliar micro-morphological analysis at subsequent stages assisted in developing plantlets with 100% survival success in V. negundo.

Does Molecular and Structural Evolution Shape the Speedy Grass Stomata?

It has been increasingly important for breeding programs to be aimed at crops that are capable of coping with a changing climate, especially with regards to higher frequency and intensity of drought events. Grass stomatal complex has been proposed as an important factor that may enable grasses to adapt to water stress and variable climate conditions. There are many studies focusing on the stomatal morphology and development in the eudicot model plant Arabidopsis and monocot model plant Brachypodium. However, the comprehensive understanding of the distinction of stomatal structure and development between monocots and eudicots, especially between grasses and eudicots, are still less known at evolutionary and comparative genetic levels. Therefore, we employed the newly released version of the One Thousand Plant Transcriptome (OneKP) database and existing databases of green plant genome assemblies to explore the evolution of gene families that contributed to the formation of the unique structure and development of grass stomata. This review emphasizes the differential stomatal morphology, developmental mechanisms, and guard cell signaling in monocots and eudicots. We provide a summary of useful molecular evidences for the high water use efficiency of grass stomata that may offer new horizons for future success in breeding climate resilient crops.

Leaf structure and chlorophyll content in Torreya grandis 'Merrillii' with Nalepella abiesis infestation

Objective The aim is to provide a theoretical basis for the prevention and control of Nalepella abiesis and to study the damage mechanism and chlorophyll content from N. abiesis on leaves of Torreya grandis 'Merrillii'. Method Dynamic changes in leaf tissue structure, stomatal structure, chloroplast ultrastructure, and chlorophyll content were studied using the fluorescence microscope, transmission electron microscope (TEM), scanning electron microscope (SEM), and spectrophotometer. Result The palisade cells changed in shape and decreased in number for an increase in days after inoculation (DAI) with mites. By the 40th day, thickness of the palisade tissue decreased considerably; spongy cells shrank; spongy tissue became looser; around stomata the cuticular peg was destroyed; guard cells shrank; and stomata shrank revealing obvious injury. Mesophyll cells gradually swelled and became deformed with the gap between cells becoming larger and larger. Also, the number of chloroplasts gradually decreased with the appearance of starch grains. By the 12th day, the number of osmiophilic granules within the chloroplast had increased with grana lamellae becoming more and more irregular in structure, especially on the 25th day, and finally disintegrating and disappearing on the 40th day. There was no significant difference in chlorophyll content between ck and the treatment with mite infection from 0 to 12 d, but a significant difference occurred from 25 to 40 d(P Conclusion N. abiesis infestation could destroy the structure of the mesophyll cells and leaf stomata of T. grandis 'Merrillii' leading to a decreased chlorophyll content that could affect photosynthesis.

Stress Protective Effect of Rhododendron arboreum Leaves (MEL) on Chromium-Treated Vigna radiata Plants

Oxidative stress due to hexavalent chromium [Cr(VI)] in Vigna radiata seedlings, and stress amelioration with treatment of methanol extract of Rhododendron arboreum leaves was observed in the present study by analyzing growth parameters, stomatal morphology, malondialdehyde (MDA) content, histological analysis, pigment contents, Cr metal uptake, elemental analysis, and antioxidant analysis. Chromium treatment resulted in the decline of root length, shoot length, fresh weight, and dry weight. Scanning electron microscopic studies revealed that Cr treatment altered the stomatal structure. As compared to control plants, MDA content increased by 80.1% in Cr-treated plants. Histological analysis with confocal microscope confirmed the nuclear damage, membrane damage, enhanced H2O2 accumulation, and decline in pigment concentration. Atomic absorption spectrometry analysis revealed an accumulation of 43.3% Chromium in the plant tissues and decreased concentration of essential elements as consequences of Cr treatment. The methanol extract of R. arboreum leaves (MEL) alleviated Cr stress in Vigna radiata seedlings by restoring normal growth, stomatal structure, and pigment contents, as well as essential elements. Reduction in H2O2 accumulation, reduced MDA content by 29.2%, and decline in Cr accumulation to 32.8% was observed after MEL supplementation to Cr-stressed plants. Decreased nuclear and membrane damage along with increased lipid-soluble as well as water-soluble antioxidants after MEL application in Cr-stressed plants are further symptoms of stress amelioration properties of Rhododendron leaves.

The Role of Grass MUTE Orthologues During Stomatal Development.

Gas exchange between the plant and the atmosphere takes place through stomatal pores formed by paired guard cells. Grasses develop a unique stomatal structure that consists of two dumbbell-shaped guard cells flanked by lateral subsidiary cells. These structures confer a very efficient gas exchange capacity, which may have contributed to the evolutionary success of grasses. Recent works have identified orthologues of Arabidopsis MUTE in three grass species: BdMUTE in Brachypodium distachyon, BZU2/ZmMUTE in maize, and OsMUTE in rice. These genes induce the recruitment of subsidiary cells, and it appears to rely upon the ability of intercellular movement, from the guard mother cell to subsidiary mother cells, of the proteins encoded by them. Unexpectedly, this function of these grass MUTE genes contrasts with that of Arabidopsis MUTE, which promotes guard mother cell identity. These MUTE orthologues also appear to control guard mother cell fate progression, with the action of BdMUTE being less severe than those of BZU2/ZmMUTE and OsMUTE. The emerging picture unravels that grass MUTE genes have not only diverged, due to neo-functionalization, from Arabidopsis MUTE, but also among them.

Single-Molecule Long-Read Sequencing Reveals the Diversity of Full-Length Transcripts in Leaves of Gnetum (Gnetales).

The limitations of RNA sequencing make it difficult to accurately predict alternative splicing (AS) and alternative polyadenylation (APA) events and long non-coding RNAs (lncRNAs), all of which reveal transcriptomic diversity and the complexity of gene regulation. Gnetum, a genus with ambiguous phylogenetic placement in seed plants, has a distinct stomatal structure and photosynthetic characteristics. In this study, a full-length transcriptome of Gnetum luofuense leaves at different developmental stages was sequenced with the latest PacBio Sequel platform. After correction by short reads generated by Illumina RNA-Seq, 80,496 full-length transcripts were obtained, of which 5269 reads were identified as isoforms of novel genes. Additionally, 1660 lncRNAs and 12,998 AS events were detected. In total, 5647 genes in the G. luofuense leaves had APA featured by at least one poly(A) site. Moreover, 67 and 30 genes from the bHLH gene family, which play an important role in stomatal development and photosynthesis, were identified from the G. luofuense genome and leaf transcripts, respectively. This leaf transcriptome supplements the reference genome of G. luofuense, and the AS events and lncRNAs detected provide valuable resources for future studies of investigating low photosynthetic capacity of Gnetum.

Nitric oxide- induced AtAO3 differentially regulates plant defense and drought tolerance in Arabidopsis thaliana

BackgroundExposure of plants to different environmental insults instigates significant changes in the cellular redox tone driven in part by promoting the production of reactive nitrogen species. The key player, nitric oxide (NO) is a small gaseous diatomic molecule, well-known for its signaling role during stress. In this study, we focused on abscisic acid (ABA) metabolism-related genes that showed differential expression in response to the NO donor S-nitroso-l-cysteine (CySNO) by conducting RNA-seq-based transcriptomic analysis.ResultsCySNO-induced ABA-related genes were identified and further characterized. Gene ontology terms for biological processes showed most of the genes were associated with protein phosphorylation. Promoter analysis suggested that several cis-regulatory elements were activated under biotic and/or abiotic stress conditions. The ABA biosynthetic gene AtAO3 was selected for validation using functional genomics. The loss of function mutant atao3 was found to differentially regulate oxidative and nitrosative stress. Further investigations for determining the role of AtAO3 in plant defense suggested a negative regulation of plant basal defense and R-gene-mediated resistance. The atao3 plants showed resistance to virulent Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000) with gradual increase in PR1 gene expression. Similarly, atao3 plants showed increased hypersensitive response (HR) when challenged with Pst DC3000 (avrB). The atgsnor1–3 and atsid2 mutants showed a susceptible phenotype with reduced PR1 transcript accumulation. Drought tolerance assay indicated that atao3 and atnced3 ABA-deficient mutants showed early wilting, followed by plant death. The study of stomatal structure showed that atao3 and atnced3 were unable to close stomata even at 7 days after drought stress. Further, they showed reduced ABA content and increased electrolyte leakage than the wild-type (WT) plants. The quantitative polymerase chain reaction analysis suggested that ABA biosynthesis genes were down-regulated, whereas expression of most of the drought-related genes were up-regulated in atao3 than in WT.ConclusionsAtAO3 negatively regulates pathogen-induced salicylic acid pathway, although it is required for drought tolerance, despite the fact that ABA production is not totally dependent on AtAO3, and that drought-related genes like DREB2 and ABI2 show response to drought irrespective of ABA content.

Physiological responses and transcriptome analysis of the Kochia prostrata (L.) Schrad. to seedling drought stress.

Kochia prostrata is a good forage plant, which has important economic and ecological value in arid and semi-arid regions of China. Drought is one of the main factors affecting its productivity. At present, there are few studies on the mechanism of drought resistance. In order to reveal the changes of physiological and biochemical indexes, stomatal structure and gene expression profiles of Kochia prostrata under drought treatment, the classical determination method and high-throughput Illumina Hiseq sequencing platform were applied to the control group (CK) and drought treatment group of Kochia prostrata. The results showed that under the condition of moderate to mild drought stress, the SOD activity reached the maximum value of 350.68 U/g min on the 5th day of stress, and under the condition of severe drought stress, the SOD activity reached the maximum on the 2nd day of stress. The accumulation of Proline remained at a high level on the 5th day of stress, and there was at least one epidermal cell interval between the two adult stomatal of the leaf epidermis, so that the evaporation shell of each stomatal did not overlap, it ensures the efficient gas exchange of the stomatal, indicating that the Kochia prostrata has strong drought resistance. A total of 1,177.46 M reads were obtained by sequencing, with a total of 352.25 Gbp data and Q30 of 85%. In the differential gene annotation to the biological process (BP), a total of 261 GO terms were enriched in the up-regulated genes, and a total of 231 GO terms were enriched in the down-regulated genes. The differentially expressed genes (DEGs) were obtained in 27 KEGG metabolic pathways, which laid a foundation for revealing the molecular mechanism of drought tolerance.

Thermal Benefits From White Variegation of Silybum marianum Leaves.

Leaves of the spiny winter annual Silybum marianum express white patches (variegation) that can cover significant surface areas, the outcome of air spaces formed between the epidermis and the green chlorenchyma. We asked: (1) what characterizes the white patches in S. marianum and what differs them from green patches? (2) Do white patches differ from green patches in photosynthetic efficiency under lower temperatures? We predicted that the air spaces in white patches have physiological benefits, elevating photosynthetic rates under low temperatures. To test our hypotheses we used both a variegated wild type and entirely green mutants. We grew the plants under moderate temperatures (20°C/10°C d/n) and compared them to plants grown under lower temperatures (15°C/5°C d/n). The developed plants were exposed to different temperatures for 1 h and their photosynthetic activity was measured. In addition, we compared in green vs. white patches, the reflectance spectra, patch structure, chlorophyll and dehydrin content, stomatal structure, plant growth, and leaf temperature. White patches were not significantly different from green patches in their biochemistry and photosynthesis. However, under lower temperatures, variegated wild-type leaves were significantly warmer than all-green mutants – possible explanations for that are discussed These findings support our hypothesis, that white variegation of S. marianum leaves has a physiological role, elevating leaf temperature during cold winter days.

Effects of exogenous Ca2+ on stomatal traits, photosynthesis, and biomass of maize seedings under salt stress.

Understanding the responses of stomatal structure, photosynthesis and biomass of maize to exogenous Ca2+ addition under NaCl stress has important significance for further uncovering the alleviative mechanism of exogenous Ca2+ on maize under salt stress. We examined the effects of exogenous Ca2+(0, 5, 10, 20, 40, 80 mmol·L-1) on the stomatal structure, photosynthesis and biomass of maize (Zea mays L. cv. Jingke 665) seedlings under NaCl stress (100 mmol·L-1). Our results showed that exogenous Ca2+ addition had limited effect on stomatal density, but significantly decreased stomatal shape index, stomatal area, stomatal length, stomatal width, and stomatal cir-cumference. Meanwhile, the net photosynthetic rate (Pn) initially increased and then decreased with the increases of exogenous Ca2+ concentration, whereas both the stomatal conductance (gs) and intercellular CO2 concentration (Ci) were decreased, suggesting that the decrease of Pn was mainly due to stomatal limitation under high Ca2+ concentration. The biomass of maize seedlings was increased and the root/shoot ratio was decreased with the increases of exogenous Ca2+ concentration, suggested that the alleviated effect of exogenous Ca2+ on aboveground biomass was higher than that on belowground biomass of maize under salt stress.

Loss or duplication of key regulatory genes coincides with environmental adaptation of the stomatal complex in Nymphaea colorata and Kalanchoe laxiflora

The stomatal complex is critical for gas and water exchange between plants and the atmosphere. Originating over 400 million years ago, the structure of the stomata has evolved to facilitate the adaptation of plants to various environments. Although the molecular mechanism of stomatal development in Arabidopsis has been widely studied, the evolution of stomatal structure and its molecular regulators in different species remains to be answered. In this study, we examined stomatal development and the orthologues of Arabidopsis stomatal genes in a basal angiosperm plant, Nymphaea colorata, and a member of the eudicot CAM family, Kalanchoe laxiflora, which represent the adaptation to aquatic and drought environments, respectively. Our results showed that despite the conservation of core stomatal regulators, a number of critical genes were lost in the N. colorata genome, including EPF2, MPK6, and AP2C3 and the polarity regulators BASL and POLAR. Interestingly, this is coincident with the loss of asymmetric divisions during the stomatal development of N. colorata. In addition, we found that the guard cell in K. laxiflora is surrounded by three or four small subsidiary cells in adaxial leaf surfaces. This type of stomatal complex is formed via repeated asymmetric cell divisions and cell state transitions. This may result from the doubled or quadrupled key genes controlling stomatal development in K. laxiflora. Our results show that loss or duplication of key regulatory genes is associated with environmental adaptation of the stomatal complex.

Experimental warming enhances the carbon gain but does not affect the yield of maize (Zea mays L.) in the North China Plain

Temperature response and sensitivity of photosynthesis and respiration are critical for projection of changes in the carbon exchange and net primary production of terrestrial ecosystems under global warming. Understanding the mechanisms and processes of photosynthetic and respiratory acclimation in response to warming may shed further lights on the change of crop yield in agricultural ecosystems in a warmer climate regime. We examined the temperature responses and sensitivity of net photosynthetic rate (An) and dark respiration (Rd) for exploring the mechanisms of thermal acclimation associated with physiological and biochemical processes affecting maize yield in the North China Plain with a field manipulative warming experiment. We found that warming substantially enhanced the carbon gain of maize plants through facilitating CO2 diffusion from ambient air to chloroplasts by altering stomatal structure and spatial distribution pattern, and benefitting CO2 assimilation efficiency with smaller vascular bundles and bigger chloroplasts. Moreover, we also found that acclimation of An to temperature (T), evidenced by the upward shift of An–T, was determined by the maximum velocity of Rubisco carboxylation (Vcmax), the maximum rate of electron transport (Jmax), and the stomatal-regulated CO2 diffusion process, whereas the balance between respiration and gross photosynthetic rate (Rd/Ag), and/or regeneration of RuBP and the Rubisco carboxylation (Jmax/Vcmax) made little contribution to the thermal acclimation of An in maize plants. In addition, temperature response and sensitivity of Rd was closely associated with the changes in foliar N concentration induced by warming. As a result, experimental warming barely affected the yield and biomass of maize plants. These results suggest that the impacts of future climate warming on maize production may be mitigated or even offset by the leaf-level thermal acclimation of photosynthesis and respiration. Our findings may have important implications for improving the accuracy of process-based ecosystem models and advancing the understanding on the interactions between ecosystem functions and climate warming.

Screening and Identification of Upland Rice Lines Derived Recurrent Selection for Drought Tolerance

Variety assemblings for higher yield capacity of upland rice which tolerant to drought stress and highly adaptable to climate change has been needed to support the effort to increase both rice yield and the upland rice field extensification. This research aims to screen and identify an agronomic character of upland rice lines as the result of recurrent selection to a seedling stage on the drought stress. Materials were 180 rice lines as the result of recurrent selections from two local varieties Sriwijaya and Bugis with other two drought tolerant lines IR7858-1 and N148+. Twenty seeds each genotype were seeding in seed pods adjusted with stripe check such Situbagendit and Inpari 6 as tolerant and susceptible lines respectively. Drought stress treatment had conducted in a week, began at two weeks seedling age with a scoring value 0-9 (SES IRRI), at the same time were taken sample soil to measure the soil water content was done at a depth of 20 cm. Then, the crops were watered again to observe the recovery capacity of the crops, with the scoring 1-9 (SES IRRI). Anatomically stomatal proximation was observed for both susceptible and tolerant rice lines. The selected lines would transplant in the field to record the yield capacity and other agronomic characters. The SES screening resulted in 53 tolerant lines, 99 moderate tolerant, and 28 susceptible to the drought stress which had the soil water content ranged from 11.9 to 12.7 percent. Anatomic stomatal observation showed that the stomatal structure and density of susceptible lines were closer and more than tolerant lines. The highest percentage of filled grains showed by the intercross line Sriwijaya/IR7858-1 about 77.4 to 85.1 percent with averagely 80.7 percent, which was a high category with the scale of 3 SES IRRI. The selected drought stress lines with better agronomic character would continuously test to know the yield capacity in the environmentally specific location.

Opportunistic survival strategy ofWelwitschia mirabilis: recent anatomical and ecophysiological studies elucidating stomatal behaviour and photosynthetic potential

We present new findings on leaf and stomatal apparatus anatomy and ecophysiology of Welwitschia mirabilis Hook.f. that are relevant to survival in the desert. We show that the structure of the stomatal apparatus with thin areas in the guard cell walls is a key feature enabling an opportunistic survival strategy through reversible quick switch-over from water conservation to CO2assimilation. Desert environment and greenhouse data demonstrated that stomatal conductance increased almost immediately after dawn to reach a maximum within approximately an hour, whereupon a steep decrease occurred. After discontinuation of induced drought in potted plants, fast recovery of stomatal conductance occurred while copious new root hairs developed within 50 h. Stomatal limitation proved to be the main photosynthetic constraint under induced drought. Under severe drought stress, biochemical limitation came into play. Chlorophyll fluorescence data of in-situ plants showed that the photosynthetic potential of leaf tissue is highest near the basal meristem, but although it decreases with age, it retains activity up to the leaf apex at the end of the green part. The photosynthetic potential of potted plants was optimal at 20 °C, analogous to mesophytic plants. Our data confirms our hypothesis that leaf surface and stomatal structure play a crucial role in moisture conservation and moderating leaf temperature for desert survival.

Specialized stomatal humidity responses underpin ecological diversity in C3 bromeliads.

The Neotropical Bromeliaceae display an extraordinary level of ecological variety, with species differing widely in habit, photosynthetic pathway and growth form. Divergences in stomatal structure and function, hitherto understudied in treatments of bromeliad evolutionary physiology, could have been critical to the generation of variety in ecophysiological strategies among the bromeliads. Because humidity is a key factor in bromeliad niches, we focussed on stomatal responses to vapour pressure deficit (VPD). We measured the sensitivity of stomatal conductance and assimilation rate to VPD in eight C3 bromeliad species of contrasting growth forms and ecophysiological strategies and parameterised the kinetics of stomatal responses to a step change in VPD. Notably, three tank-epiphyte species displayed low conductance, high sensitivity and fast kinetics relative to the lithophytes, while three xeromorphic terrestrial species showed high conductance and sensitivity but slow stomatal kinetics. An apparent feedforward response of transpiration to VPD occurred in the tank epiphytes, while water-use efficiency was differentially impacted by stomatal closure depending on photosynthetic responses. Differences in stomatal responses to VPD between species of different ecophysiological strategies are closely linked to modifications of stomatal morphology, which we argue has been a pivotal component of the evolution of high diversity in this important plant family.