Stu-miR827-Targeted StWRKY48 Transcription Factor Negatively Regulates Drought Tolerance of Potato by Increasing Leaf Stomatal Density.

Stomata are specialized portals in plant leaves to modulate water loss from plants to the atmosphere by control of the transpiration, thereby determining the water-use efficiency and drought resistance of plants. Despite that the stomata developmental progression is well-understood at the molecular level, the experimental evidence that miRNA regulates stomata development is still lacking, and the underlying mechanism remains elusive. This study demonstrates the involvement of stu-miR827 in regulating the drought tolerance of potato due to its control over the leaf stomatal density. The expression analysis showed that stu-miR827 was obviously repressed by drought stresses and then rapidly increased after rewatering. Suppressing the expression of stu-miR827 transgenic potato lines showed an increase in stomatal density, correlating with a weaker drought resistance compared with wildtype potato lines. In addition, StWRKY48 was identified as the target gene of stu-miR827, and the expression of StWRKY48 was obviously induced by drought stresses and was greatly upregulated in stu-miR827 knockdown transgenic potato lines, suggesting its involvement in the drought stress response. Importantly, the expression of genes associated with stomata development, such as SDD (stomatal density and distribution) and TMM (too many mouths), was seriously suppressed in transgenic lines. Altogether, these observations demonstrated that suppression of stu-miR827 might lead to overexpression of StWRKY48, which may contribute to negatively regulating the drought adaptation of potato by increasing the stomatal density. The results may facilitate functional studies of miRNAs in the process of drought tolerance in plants.

Green Tea Catechins, (-)-Catechin Gallate, and (-)-Gallocatechin Gallate are Potent Inhibitors of ABA-Induced Stomatal Closure.

Stomatal movement is indispensable for plant growth and survival in response to environmental stimuli. Cytosolic Ca2+ elevation plays a crucial role in ABA-induced stomatal closure during drought stress; however, to what extent the Ca2+ movement across the plasma membrane from the apoplast to the cytosol contributes to this process still needs clarification. Here the authors identify (-)-catechin gallate (CG) and (-)-gallocatechin gallate (GCG), components of green tea, as inhibitors of voltage-dependent K+ channels which regulate K+ fluxes in Arabidopsis thaliana guard cells. In Arabidopsis guard cells CG/GCG prevent ABA-induced: i) membrane depolarization; ii) activation of Ca2+ permeable cation (ICa ) channels; and iii) cytosolic Ca2+ transients. In whole Arabidopsis plants co-treatment with CG/GCG and ABA suppressed ABA-induced stomatal closure and surface temperature increase. Similar to ABA, CG/GCG inhibited stomatal closure is elicited by the elicitor peptide, flg22 but has no impact on dark-induced stomatal closure or light- and fusicoccin-induced stomatal opening, suggesting that the inhibitory effect of CG/GCG is associated with Ca2+ -related signaling pathways. This study further supports the crucial role of ICa channels of the plasma membrane in ABA-induced stomatal closure. Moreover, CG and GCG represent a new tool for the study of abiotic or biotic stress-induced signal transduction pathways.

Cytosolic and Nucleosolic Calcium-Regulated Molecular Networks in Response to Long-Term Treatment with Abscisic Acid and Methyl Jasmonate in Arabidopsis thaliana.

Calcium acts as a universal secondary messenger that transfers developmental cues and stress signals for gene expression and adaptive growth. A prior study showed that abiotic stresses induce mutually independent cytosolic Ca2+ ([Ca2+]cyt) and nucleosolic Ca2+ ([Ca2+]nuc) increases in Arabidopsis thaliana root cells. However, gene expression networks deciphering [Ca2+]cyt and [Ca2+]nuc signalling pathways remain elusive. Here, using transgenic A. thaliana to selectively impair abscisic acid (ABA)- or methyl jasmonate (MeJA)-induced [Ca2+]cyt and [Ca2+]nuc increases, we identified [Ca2+]cyt- and [Ca2+]nuc-regulated ABA- or MeJA-responsive genes with a genome oligo-array. Gene co-expression network analysis revealed four Ca2+ signal-decoding genes, CAM1, CIPK8, GAD1, and CPN20, as hub genes co-expressed with Ca2+-regulated hormone-responsive genes and hormone signalling genes. Luciferase complementation imaging assays showed interactions among CAM1, CIPK8, and GAD1; they also showed interactions with several proteins encoded by Ca2+-regulated hormone-responsive genes. Furthermore, CAM1 and CIPK8 were required for MeJA-induced stomatal closure; they were associated with ABA-inhibited seed germination. Quantitative reverse transcription polymerase chain reaction analysis showed the unique expression pattern of [Ca2+]-regulated hormone-responsive genes in cam1, cipk8, and gad1. This comprehensive understanding of distinct Ca2+ and hormonal signalling will allow the application of approaches to uncover novel molecular foundations for responses to developmental and stress signals in plants.

Biosystematic studies of some Egyptian species of Cestrum (Solanaceae).

Cestrum is the second largest genus of family Solanaceae, after Solanum, distributed in warm to subtropical regions. Species of genus Cestrum are one of the most ethnopharmacological relevant plants, for their broad biological and pharmacological properties. There is a scarcity to taxonomical studies and identification of these plants in Egypt, thus, the objective of this study was to implement various morphological features, chemical markers and molecular tools to emphasize the taxonomical features of the different Cestrum species. Morphologically, the epidermal cells of C. diurnum, C. elegans and C. parqui were irregular with sinuate anticlinal wall patterns for both surfaces, while, C. nocturnum has anticlinal walls, sinuolate with polygonal to irregular epidermal cells on the abaxial surface. The species of Cestrum have hypostomatic leaves, except C. parqui that has amphistomatic leaves. The experimented species of Cestrum have Anomocytic and anisocytic stomata, while, C. elegans has a diacytic stomata. The morphologically identified Cestrum spp were molecular confirmed based on their ITS sequences, the sequences of C. diurnum, C. nocturnum, C. elegans and C. parqui were deposited on genbank with accession # MT742788.1, MT749390.1, MW091481.1 and MW023744.1, respectively. From the SCOT analyses, the four species of Cestrum were grouped into 2 clusters (I, II), cluster I contains C. elegans, C. nocturnum and C. parqui, while cluster II contains only C. diurnum with 100% polymorphism for all primers. From the GC-MS profile, the C. diurnum exhibited a diverse metabolic paradigm, ensuring their richness with different metabolites comparing to other experimented Cestrum species. Among the total resolved metabolites, 15-methyltricyclo 6.5.2-pentadeca-1,3,5,7,9, 11,13-heptene was the highly incident compound in C. elegans (35.89%) followed by C. parqui (21.81%) and C. diurnum (11.28%), while it absent on C. nocturnum. The compound, 2,2',6,6'-tetra-tert-butyl-4,4'-methylenediphenol was highly detected in C. elegans and C. dirunum with minor amounts in the other Cestrum species. Cypermethrin and 3-butynyl-2,2,5-trimethyl-1,3-dioxane-5-methanol were pivotally reported in C. nocturnum. Taken together, from molecular and metabolic markers, C. diurnum, C. parqui and C. elegans have higher proximity unlike to C. nocturnum.

Atmospheric pressure plasma treatment induces abscisic acid production, reduces stomatal aperture and improves seedling growth in Arabidopsis thaliana.

Cold atmospheric pressure plasmas (CAPPs) have been widely used for pre-sowing treatment in agriculture to accelerate seed germination; however, information on their application to pre-transplant seedlings is scarce. The roles of the phytohormone abscisic acid (ABA) on guard cell aperture that control air exchange with the environment were investigated after CAPPs treatment. In this study, Arabidopsis thaliana seedling growth was evaluated under CAPPs treatment at different doses. Besides, the optimal growth stimulation dose was selected to further evaluate changes in ABA, ROS, Ca2+ and stomatal aperture during growth .The expression of most ABA signalling genes were aslo examined to investigate the mechanism. CAPPs treatment for 1 min significantly promoted Arabidopsis seedling growth; the ABA concentration in seedlings increased and peaked 48 h after treatment but was lower than in the control after 96 h. Transcript levels of most ABA signalling genes were markedly enhanced at 48 h, although their transcripts were significantly downregulated after 96 h. CAPPs treatment also reduced stomatal aperture after 24 h and accelerated ROS accumulation in guard cells. The Ca2+ concentration in the treatment group was markedly higher than in the control at 24 and 96 h. The results suggest that CAPPs treatment accelerates ABA accumulation in Arabidopsis at early growth stages and ABA regulates ROS and Ca2+ concentrations to affect stomatal aperture, and both ABA and stoma size are affected in CAPPs stimulation of Arabidopsis seedling growth.

Effect of Iron Source and Medium pH on Growth and Development of Sorbus commixta In Vitro.

Sorbus commixta is a valuable hardwood plant with a high economical value for its medicinal and ornamental qualities. The aim of this work was to investigate the effects of the iron (Fe) source and medium pH on the growth and development of S. commixta in vitro. The Fe sources used, including non-chelated iron sulfate (FeSO4), iron ethylenediaminetetraacetic acid (Fe-EDTA), and iron diethylenetriaminepentaacetic acid (Fe-DTPA), were supplemented to the Multipurpose medium with a final Fe concentration of 2.78 mg·L-1. The medium without any supplementary Fe was used as the control. The pH of the agar-solidified medium was adjusted to either 4.70, 5.70, or 6.70. The experiment was conducted in a culture room for six weeks with 25 °C day and night temperatures, and a 16-h photoperiod with a light intensity of 50 mmol·m-2·s-1 photosynthetic photon flux density (PPFD). Both the Fe source and pH affected the growth and development of the micropropagated plants in vitro. The leaves were greener in the pH 4.70 and 5.70 treatments. The tissue Fe content decreased with the increase of the medium pH. The leaf chlorophyll content was similar between plants treated with FeSO4 and those with Fe-EDTA. The numbers of the shoots and roots of plantlets treated with FeSO4 were 2.5 and 2 times greater than those of the control, respectively. The fresh and dry weights of the shoot and the root were the greatest for plants treated with Fe-EDTA combined with pH 5.70. The calcium, magnesium, and manganese contents in the plantlets increased in the pH 5.70 treatments regardless of the Fe source. Supplementary Fe decreased the activity of ferric chelate reductase. Overall, although the plantlets absorbed more Fe at pH 4.70, Fe-EDTA combined with pH 5.70 was found to be the best for the growth and development of S. commixta in vitro.

Silicon changes C:N:P stoichiometry of sugarcane and its consequences for photosynthesis, biomass partitioning and plant growth.

Silicon (Si) application has improved yield and stress tolerance in sugarcane crops. In this respect, C:N:P stoichiometry makes it possible to identify flows and interaction between elements in plants and their relationship with growth. However, few studies have investigated the influence of Si on physiological variables and C:N:P stoichiometry in sugarcane. As such, this study aimed to assess the effect of increasing Si concentrations on the growth and stoichiometric composition of sugarcane plants in the early growth stage. The experiment was conducted in pots, using four Si concentrations (0, 0.8, 1.6 and 3.2 mM). Biomass production, the concentration and accumulation of C, N, P and Si as well as the relationship between them were assessed. Silicon application increased biomass production, the rate of photosynthesis, instantaneous carboxylation efficiency and C, N, P and Si accumulation, in addition to altering stoichiometric ratios (C:N, C:P, N:P and C:Si) in different parts of the plants. The decline in C concentration associated with greater N and P absorption indicates that Si favoured physiological processes, which is reflected in biomass production. Our results demonstrate that Si supply improved carbon use efficiency, directly influencing sugarcane yield as well as C and nutrient cycling.

Sugar Beet (Beta vulgaris) Guard Cells Responses to Salinity Stress: A Proteomic Analysis.

Soil salinity is a major environmental constraint affecting crop growth and threatening global food security. Plants adapt to salinity by optimizing the performance of stomata. Stomata are formed by two guard cells (GCs) that are morphologically and functionally distinct from the other leaf cells. These microscopic sphincters inserted into the wax-covered epidermis of the shoot balance CO2 intake for photosynthetic carbon gain and concomitant water loss. In order to better understand the molecular mechanisms underlying stomatal function under saline conditions, we used proteomics approach to study isolated GCs from the salt-tolerant sugar beet species. Of the 2088 proteins identified in sugar beet GCs, 82 were differentially regulated by salt treatment. According to bioinformatics analysis (GO enrichment analysis and protein classification), these proteins were involved in lipid metabolism, cell wall modification, ATP biosynthesis, and signaling. Among the significant differentially abundant proteins, several proteins classified as "stress proteins" were upregulated, including non-specific lipid transfer protein, chaperone proteins, heat shock proteins, inorganic pyrophosphatase 2, responsible for energized vacuole membrane for ion transportation. Moreover, several antioxidant enzymes (peroxide, superoxidase dismutase) were highly upregulated. Furthermore, cell wall proteins detected in GCs provided some evidence that GC walls were more flexible in response to salt stress. Proteins such as L-ascorbate oxidase that were constitutively high under both control and high salinity conditions may contribute to the ability of sugar beet GCs to adapt to salinity by mitigating salinity-induced oxidative stress.

Element content and expression of genes of interest in guard cells are connected to spatiotemporal variations in stomatal conductance.

Element content and expression of genes of interest on single cell types, such as stomata, provide valuable insights into their specific physiology, improving our understanding of leaf gas exchange regulation. We investigated how far differences in stomatal conductance (gs ) can be ascribed to changes in guard cells functioning in amphistomateous leaves. gs was measured during the day on both leaf sides, on well-watered and drought-stressed trees (two Populus euramericana Moench and two Populus nigra L. genotypes). In parallel, guard cells were dissected for element content and gene expressions analyses. Both were strongly arranged according to genotype, and drought had the lowest impact overall. Normalizing the data by genotype highlighted a structure on the basis of leaf sides and time of day both for element content and gene expression. Guard cells magnesium, phosphorus, and chlorine were the most abundant on the abaxial side in the morning, where gs was at the highest. In contrast, genes encoding H+ -ATPase and aquaporins were usually more abundant in the afternoon, whereas genes encoding Ca2+ -vacuolar antiporters, K+ channels, and ABA-related genes were in general more abundant on the adaxial side. Our work highlights the unique physiology of each leaf side and their analogous rhythmicity through the day.

Callose and homogalacturonan epitope distribution in stomatal complexes of Zea mays and Vigna sinensis.

This article deals with the distribution of callose and of the homogalacturonan (HG) epitopes recognized by LM20, JIM5, and 2F4 antibodies in cell walls of differentiating and functioning stomatal complexes of the monocotyledon Zea mays and the dicotyledon Vigna sinensis. The findings revealed that, during stomatal development, in these plant species, callose appears in an accurately spatially and timely controlled manner in cell walls of the guard cells (GCs). In functioning stomata of both plants, callose constitutes a dominant cell wall matrix material of the polar ventral cell wall ends and of the local GC cell wall thickenings. In Zea mays, the LM20, JIM5, or 2F4 antibody-recognized HG epitopes were mainly located in the expanding cell wall regions of the stomatal complexes, while in Vigna sinensis, they were deposited in the local cell wall thickenings of the GCs as well as at the ledges of the stomatal pore. Consideration of the presented data favors the view that in the stomatal complexes of the monocotyledon Z. mays and the dicotyledon V. sinensis, the esterified HGs contribute to the cell wall expansion taking place during GC morphogenesis and the opening of the stomatal pore. Besides, callose and the highly de-esterified HGs allow to GC cell wall regions to withstand the mechanical stresses exerted during stomatal function.

Phosphorus-zinc interactions in cotton: consequences for biomass production and nutrient-use efficiency in photosynthesis.

The fragmentary information on phosphorus (P) × zinc (Zn) interactions in plants warrants further study, particularly in plants known for their high P and Zn requirements, such as cotton (Gossypium hirsutum L.). The objective of this study was to investigate the effect of P × Zn interactions in a modern cultivar of cotton grown hydroponically. Biomass, mineral nutrition and photosynthetic parameters were monitored in plants receiving contrasting combinations of P and Zn supply. Root biomass, length and surface area were similar in plants with low P and/or low Zn supply to those in plants grown with high P and high Zn supply, reflecting an increased root/shoot biomass quotient when plants lack sufficient P or Zn for growth. Increasing P supply and reducing Zn supply increased shoot P concentrations, whilst shoot Zn concentrations were influenced largely by Zn supply. A balanced P × Zn supply (4 mM P × 4 µM Zn) enabled greatest biomass accumulation, while an imbalanced supply of these nutrients led to Zn deficiency, P toxicity or Zn toxicity. Net photosynthetic rate, stomatal conductance, transpiration rate and instantaneous carboxylation efficiency increased as P or Zn supply increased. Although increasing P supply reduced the P-use efficiency in photosynthesis (PUEP) and increasing Zn supply reduced the Zn-use efficiency in photosynthesis (ZnUEP), increasing Zn supply at a given P supply increased PUEP and increasing P supply at a given Zn supply increased ZnUEP. These results suggest that agricultural management strategies should seek for balanced mineral nutrition to optimize yields and resource-use efficiencies.

The water relations and xylem attributes of albino redwood shoots (Sequioa sempervirens (D. Don.) Endl.).

Plants that lack chlorophyll are rare and typically restricted to holoparasites that obtain their carbon, water and mineral resources from a host plant. Although not parasites in the traditional sense, albino foliage, such as the sprouts that sometimes develop from redwood tree trunks, are comparable in function. They occur sporadically, and can reach the size of shrubs and in rare cases, trees. Albino redwoods are interesting because in addition to their reduced carbon resources, the absence of chloroplasts may impede proper stomatal function, and both aspects may have upstream consequences on water transport and xylem quality. We examined the water relations, water transport and xylem anatomical attributes of albino redwoods and show that similar to achlorophyllous and parasitic plants, albino redwoods have notably higher stomatal conductance than green sprouts. Given that stem xylem tracheid size as well as water transport efficiency are nearly equivalent in both albino and green individuals, we attribute the increased leaf water loss in albino sprouts to lower leaf to xylem area ratios, which favour improved hydration relative to green sprouts. The stems of albino redwoods were more vulnerable to drought-induced embolism than green stems, and this was consistent with the albino's weaker tracheids, as characterized by wall thickness to lumen diameter measures. Our results are both complementary and consistent with previous research on achlorophyllous plants, and suggest that the loss of stomatal control and photosynthetic capacity results in substantial vascular and anatomical adjustments.

Relationships of CO2 assimilation rates with exposure- and flux-based O3 metrics in three urban tree species.

The relationships of CO2 assimilation under saturated-light conditions (Asat) with exposure- (AOTX, Accumulated Ozone exposure over a hourly Threshold of X ppb) and flux-based (PODY, Phytotoxic Ozone Dose over a hourly threshold Y nmol·m-2·s-1) O3 metrics was studied on three common urban trees, Fraxinus chinensis (FC), Platanus orientalis (PO) and Robinia pseudoacacia (RP). Parameterizations for a stomatal multiplicative model were proposed for the three species. RP was the species showing lower species-specific maximum stomatal conductance (gmax) and experiencing lower cumulative O3 uptake along the experiment, but in contrast it was the most sensitive to O3. PODY was slightly better than AOTX metric at estimating relative Asat (R-Asat)for PO and RB but not for FC. The best fittings obtained for the regressions between R-Asat and AOTX for FC, PO and RP were 0.904, 0.868, and 0.876, when the thresholds of X were 60ppb, 55ppb and 30ppb, respectively. However, AOT40 performed also well for all of them, with R2 always >0.83. For PODY, the highest R2 values for FC, PO and RB were 0.863, 0.897 and 0.911 at thresholds Y=7, 5 and 1nmolO3m-2s-1, respectively. Given the potentially higher O3 removal capacity of FC and PO by stomatal uptake and their lower sensitivity to this pollutant than RP, the former two species would be appropriate for urban gardens and areas where O3 levels are high. Parameterization and modeling of stomatal conductance for the main urban tree species may provide reliable estimations of the stomatal uptake of O3 and other gaseous pollutants by vegetation, which may support decision making on the most suitable species for green urban planning in polluted areas.

Metabolic Signatures in Response to Abscisic Acid (ABA) Treatment in Brassica napus Guard Cells Revealed by Metabolomics.

Drought can severely damage crops, resulting in major yield losses. During drought, vascular land plants conserve water via stomatal closure. Each stomate is bordered by a pair of guard cells that shrink in response to drought and the associated hormone abscisic acid (ABA). The activation of complex intracellular signaling networks underlies these responses. Therefore, analysis of guard cell metabolites is fundamental for elucidation of guard cell signaling pathways. Brassica napus is an important oilseed crop for human consumption and biodiesel production. Here, non-targeted metabolomics utilizing gas chromatography mass spectrometry (GC-MS/MS) and liquid chromatography mass spectrometry (LC-MS/MS) were employed for the first time to identify metabolic signatures in response to ABA in B. napus guard cell protoplasts. Metabolome profiling identified 390 distinct metabolites in B. napus guard cells, falling into diverse classes. Of these, 77 metabolites, comprising both primary and secondary metabolites were found to be significantly ABA responsive, including carbohydrates, fatty acids, glucosinolates, and flavonoids. Selected secondary metabolites, sinigrin, quercetin, campesterol, and sitosterol, were confirmed to regulate stomatal closure in Arabidopsis thaliana, B. napus or both species. Information derived from metabolite datasets can provide a blueprint for improvement of water use efficiency and drought tolerance in crops.

Expression of the MYB transcription factor gene BplMYB46 affects abiotic stress tolerance and secondary cell wall deposition in Betula platyphylla.

Plant MYB transcription factors control diverse biological processes, such as differentiation, development and abiotic stress responses. In this study, we characterized BplMYB46, an MYB gene from Betula platyphylla (birch) that is involved in both abiotic stress tolerance and secondary wall biosynthesis. BplMYB46 can act as a transcriptional activator in yeast and tobacco. We generated transgenic birch plants with overexpressing or silencing of BplMYB46 and subjected them to gain- or loss-of-function analysis. The results suggest that BplMYB46 improves salt and osmotic tolerance by affecting the expression of genes including SOD, POD and P5CS to increase both reactive oxygen species scavenging and proline levels. In addition, BplMYB46 appears to be involved in controlling stomatal aperture to reduce water loss. Overexpression of BplMYB46 increases lignin deposition, secondary cell wall thickness and the expression of genes in secondary cell wall formation. Further analysis indicated that BplMYB46 binds to MYBCORE and AC-box motifs and may directly activate the expression of genes involved in abiotic stress responses and secondary cell wall biosynthesis whose promoters contain these motifs. The transgenic BplMYB46-overexpressing birch plants, which have improved salt and osmotic stress tolerance, higher lignin and cellulose content and lower hemicellulose content than the control, have potential applications in the forestry industry.

Stomatal Function Requires Pectin De-methyl-esterification of the Guard Cell Wall.

Stomatal opening and closure depends on changes in turgor pressure acting within guard cells to alter cell shape [1]. The extent of these shape changes is limited by the mechanical properties of the cells, which will be largely dependent on the structure of the cell walls. Although it has long been observed that guard cells are anisotropic due to differential thickening and the orientation of cellulose microfibrils [2], our understanding of the composition of the cell wall that allows them to undergo repeated swelling and deflation remains surprisingly poor. Here, we show that the walls of guard cells are rich in un-esterified pectins. We identify a pectin methylesterase gene, PME6, which is highly expressed in guard cells and required for stomatal function. pme6-1 mutant guard cells have walls enriched in methyl-esterified pectin and show a decreased dynamic range in response to triggers of stomatal opening/closure, including elevated osmoticum, suggesting that abrogation of stomatal function reflects a mechanical change in the guard cell wall. Altered stomatal function leads to increased conductance and evaporative cooling, as well as decreased plant growth. The growth defect of the pme6-1 mutant is rescued by maintaining the plants in elevated CO2, substantiating gas exchange analyses, indicating that the mutant stomata can bestow an improved assimilation rate. Restoration of PME6 rescues guard cell wall pectin methyl-esterification status, stomatal function, and plant growth. Our results establish a link between gene expression in guard cells and their cell wall properties, with a corresponding effect on stomatal function and plant physiology.

Metabolomic Responses of Guard Cells and Mesophyll Cells to Bicarbonate.

Anthropogenic CO2 presently at 400 ppm is expected to reach 550 ppm in 2050, an increment expected to affect plant growth and productivity. Paired stomatal guard cells (GCs) are the gate-way for water, CO2, and pathogen, while mesophyll cells (MCs) represent the bulk cell-type of green leaves mainly for photosynthesis. We used the two different cell types, i.e., GCs and MCs from canola (Brassica napus) to profile metabolomic changes upon increased CO2 through supplementation with bicarbonate (HCO3-). Two metabolomics platforms enabled quantification of 268 metabolites in a time-course study to reveal short-term responses. The HCO3- responsive metabolomes of the cell types differed in their responsiveness. The MCs demonstrated increased amino acids, phenylpropanoids, redox metabolites, auxins and cytokinins, all of which were decreased in GCs in response to HCO3-. In addition, the GCs showed differential increases of primary C-metabolites, N-metabolites (e.g., purines and amino acids), and defense-responsive pathways (e.g., alkaloids, phenolics, and flavonoids) as compared to the MCs, indicating differential C/N homeostasis in the cell-types. The metabolomics results provide insights into plant responses and crop productivity under future climatic changes where elevated CO2 conditions are to take center-stage.

Ectopic expression of a hot pepper bZIP-like transcription factor in potato enhances drought tolerance without decreasing tuber yield.

Over-expression of group A bZIP transcription factor genes in plants improves abiotic stress tolerance but usually reduces yields. Thus, there have been several efforts to overcome yield penalty in transgenic plants. In this study, we characterized that expression of the hot pepper (Capsicum annuum) gene CaBZ1, which encodes a group S bZIP transcription factor, was induced by salt and osmotic stress as well as abscisic acid (ABA). Transgenic potato (Solanum tuberosum) plants over-expressing CaBZ1 exhibited reduced rates of water loss and faster stomatal closure than non transgenic potato plants under drought and ABA treatment conditions. CaBZ1 over-expression in transgenic potato increased the expression of ABA- and stress-related genes (such as CYP707A1, CBF and NAC-like genes) and improved drought stress tolerance. Interestingly, over-expression of CaBZ1 in potato did not produce undesirable growth phenotypes in major agricultural traits such as plant height, leaf size and tuber formation under normal growth conditions. The transgenic potato plants also had higher tuber yields than non transgenic potato plants under drought stress conditions. Thus, CaBZ1 may be useful for improving drought tolerance in tuber crops. This might be the first report of the production of transgenic potato with improved tuber yields under drought conditions.

Arbuscular mycorrhizal symbiosis alters stomatal conductance of host plants more under drought than under amply watered conditions: a meta-analysis.

Stomata regulate rates of carbon assimilation and water loss. Arbuscular mycorrhizal (AM) symbioses often modify stomatal behavior and therefore play pivotal roles in plant productivity. The size of the AM effect on stomatal conductance to water vapor (g s ) has varied widely, has not always been apparent, and is unpredictable. We conducted a meta-analysis of 460 studies to determine the size of the AM effect under ample watering and drought and to examine how experimental conditions have influenced the AM effect. Across all host and symbiont combinations under all soil moisture conditions, AM plants have shown 24 % higher g s than nonmycorrhizal (NM) controls. The promotion of g s has been over twice as great during moderate drought than under amply watered conditions. The AM influence on g s has been even more pronounced under severe drought, with over four times the promotion observed with ample water. Members of the Claroideoglomeraceae, Glomeraceae, and other AM families stimulated g s by about the same average amount. Colonization by native AM fungi has produced the largest promotion. Among single-AM symbionts, Glomus deserticola, Claroideoglomus etunicatum, and Funneliformis mosseae have had the largest average effects on g s across studies. Dicotyledonous hosts, especially legumes, have been slightly more responsive to AM symbiosis than monocotyledonous hosts, and C3 plants have shown over twice the AM-induced promotion of C4 plants. The extent of root colonization is important, with heavily colonized plants showing ×10 the g s promotion of lightly colonized plants. AM promotion of g s has been larger in growth chambers and in the field than in greenhouse studies, almost ×3 as large when plants were grown under high light than low light, and ×2.5 as large in purely mineral soils than in soils having an organic component. When AM plants have been compared with NM controls given NM pot culture, they have shown only half the promotion of g s as NM plants not given anything at inoculation to control for associated soil organisms. The AM effect has been much greater when AM plants were larger or had more phosphorus than NM controls. These findings should assist in further investigations of predictions and mechanisms of the AM influence on host g s .