Comparison of Stomatal Characteristics between Dendrobium loddigesii and Dendrobium candidum

[Objective]This study was to reveal the physiological and ecological mechanism of growth and development of test-tube seedlings.[Methods]Leaf stomata of test-tube seedlings of D.loddigesii and D.candidum at different growth and development stages were observed under scanning electron microscope,and their fluorescence induction response curve was assayed by using modulate fluorometer.[Results] At each growth and development stage,D.loddigesii test-tube seedling has a higher leaf stomatal density over D.candidum,while a lower stomata opening rate.Along with the growth,the size of stomata of both D.loddigesii and D.candidum did not change obviously,but their stoma density increased by 83% and 17.6% respectively.Leaf stomata opening rate reached the highest at the age of 240-day-old.Under the conditions of three settled light intensities,stomatal opening degree of D.loddigesii was increased by the intensity of illumination,the maximum aperture occurred at the light intensity of 54 μmol/m2·s.Given the same culture condition,both the maximum electron transport rate（14 μmol/m2·s）and light saturation point（318 μmol/m2·s）of D.loddigesii test-tube seedling are lower than that of D.candidum（20 μmol/m2·s,483 μmol/m2·s）.Moreover,the potential photosynthetic capacity of D.loddigesii is relatively poor.[Conclusion]The photosynthetic rate varies among different species of Dendrobium,which could be attributed to their different stomatal characteristics.Usually,the light intensity of tissue culture chamber is set up as 27 μmol/（m2·s）,where both D.loddigesii and D.candidum do not acquire an optimal state for their leaf stomatal opening.Considering the characteristics to select suitable culture condition,the stomatal aperture and photosynthetic rate could be enhanced,which can promote the growth and development of test-tube seedlings.

Disruption of the 1-deoxy-D-xylulose-5-phosphate reductoisomerase （DXR） gene results in albino, dwarf and defects in trichome initiation and stomata closure in Arabidopsis

1-Deoxy-D-xylulose-5-phosphate reductoisomerase （DXR） is an important enzyme involved in the 2-C-methyi-D- erythritol-4-phosphate （MEP） pathway which provides the basic five-carbon units for isoprenoid biosynthesis. To investigate the role of the MEP pathway in plant development and metabolism, we carried out detailed analyses on a dxr mutant （GK_215C01） and two DXR transgenic co-suppression fines, OX-DXR-L2 and OX-DXR-L7. We found that the dxr mutant was albino and dwarf. It never bolted, had significantly reduced number of trichomes and most of the stomata could not close normally in the leaves. The two co-suppression lines produced more yellow inflorescences and albino sepals with no trichomes. The transcription levels of genes involved in tricbome initiation were found to be strongly affected, including GLABRA1, TRANSPARENT TESTA GLABROUS 1, TRIPTYCHON and SPINDLY, expression of which is regulated by gibberellic acids （GAs）. Exogenous application of GA3 could partially rescue the dwarf phenotype and the trichome initiation of dxr, whereas exogenous application of abscisic acid （ABA） could rescue the stomata closure defect, suggesting that lower levels of both GA and ABA contribute to the phenotype in the dxr mutants. We further found that genes involved in the biosynthetic pathways of GA and ABA were coordinately regulated. These results indicate that disruption of the plastidial MEP pathway leads to biosynthetic deficiency of photosynthetic pigments, GAs and ABA, and thus the developmental abnormalities, and that the flux from the cytoplasmic mevalonate pathway is not sufficient to rescue the deficiency caused by the blockage of the plastidial MEP pathway. These results reveal a critical role for the MEP biosynthetic pathway in controlling the biosynthesis of isoprenoids.

REGULATING EFFECTS OF VASCULAR ENDOTHELIAL GROWTH FACTOR AND ANG Ⅱ ON FROG'S PERICARDIAL STOMATA, MESOTHELIUM AND ANGIOGENESIS

To observe the regulating effects of vascular endothelial growth factor (VEGF) and angiotensinⅡ (ANG II) on the frog’s pericardium, lymphatic stomata and angiogenesis so as to reveal their effects and mechanism on the mesothelial permeability, lymphatic stoma regulation and myocardial hypertrophy. Methods. VEGF and ANGⅡ were injected into the frog’s peritoneal cavity so as to examine the changes of the pericardial stromata by using transmission electron microscopy, scanning electron microscopy and computerized imaging analysis. Results. Scattered distributed pericardial stomata were found on the parietal pericardium of the frog with a few sinusoid mesothelial cells, whose blood supply was directly from the cardiac chambers flowing into the trabecular spaces of the myocardium (because there are no blood vessels in the myocardium of the frog). The average diameters of the pericardial stomata in VEGF and ANGⅡ groups were 1.50μ m and 1.79μ m respectively, which were much larger than those in the control group (0.72μ m, P Conclusions. VEGF and ANGⅡ could strongly regulate the pericardial stomata by increasing their numbers and openings with larger diameters and higher distribution density. They could also increase the sinusoid areas with the result of the higher permeability of the pericardium, which clearly indicated that VEGF and ANGⅡ could speed up the material transfer of the pericardial cavity and play an important role in preventing myocardial interstitial edema. Yet there was no strong evidence to show the angiogenesis in the myocardium.

Investigation of Different Characters of Stomata on Three Cocoa Clones with Resistance Level Difference to VSD （Vascular Streak dieback） Disease

The development of the science of cytology and genetics, particularly on cell structure and function provided a breakthrough for breeders and allowed for early selection. Character of stomata density on some commodities was reported as important factor to determine the disease resistance. The research was done for getting information about the differences in the stomata characters influenced on the level of Vascular Streak dieback （VSD） resistance on cocoa. The research was conducted in the Laboratory of Genetics, Gadjah Mada University and leaves samples were conducted in Kendeng Lembu Gardens, PTPN XII. The research used a split plot design with three factors included the type of clones with different levels of VSD disease resistance （PA 191, BL 703 and GS 29）, leaf position （top, middle and base） and leaf age （young and old）. Stomata characters included number of stomata, stomata opening width, stomata wide and stomata diameter were observed. The results showed that the stomata characters in three cacao genotypes with different resistance levels indicated a difference in number of stomata, stomata size, stomata opening width, stomata wide and stomata diameter. Stomata number, stomata opening width and stomata diameter on PA 191 （resistance clone） were lower than the susceptible clones （BL 703 dan GS 29）. The lowest of number and diameter stomata on the base position on the old leaves tissues. Number of stomata, stomata opening width and stomata diameter were estimated role in mechanism of VSD resistance and that were expected could be used as criteria selection to VSD resistance.

Relation of Leaf Stomatal Traits to Yield and Drought Resistance of Wheat

[ Objective] The study aimed to discuss the relation of leaf stomatal traits to yield and drought resistance of wheat. [ Method] Using the DH population of wheat cultivar Hanxuanl0/Lumai14 as the test object, the relation of leaf stomatal density （SD）, length （SL） and width （ SW）, stomatal conductance （g,）, photosynthetic rate （ Pn ）, transpiration rate （ Tr） to grain yield per plant and index of drought resistance （IDR） on the 10th and 20t＂ day after anthesis under the conditions of drought stress and normal irrigation were discussed by the methods of correlation analysis and path analysis. [ Result] Under the two water conditions, the correlations of these stomatal traits with yield components and IDR were mostly not significant on the 10t＂ day after anthesis, but there were significantly positive correlations between thousand kernel weight （TKW） and these traits on the 20^th day after anthesis. Path analysis showed that g,, Pn and Tt, were main factors affecting yield per plant （YPP） and IDR, and they had stron- ger direct effects on YPP and IDR, while their indirect interaction was also strong. The direct effects of SD, SL and SW on YPP and IDR were small, as well as their indirect action among SD, SL and SW. On the other hand, the correlations between SD and SL were significant, and the correlations of SL with SW, gn, P, and Tt, were extremely significant on the 10th and 20th day after anthesis under the two water conditions. However, the correlations of SD and SL with g,, P,, and Tr changed with water conditions or growth stages, showing that water conditions or growth stages had great effects on the correlations between two traits. Therefore, it is not always a good means to improve stomatal conductance, photosynthetic rate and transpiration rate and hence promote wheat yield by selecting stomatal density and size. [ Conclusion] The research could provide scientific references for revealing the roles of leaf stomatal traits in wheat breeding for drought resistance.

Effect of Genetic and Altitude Differences on Stomata Characters as Resistance Indicators to Vascular Streak-Dieback （VSD） in COCOA （Theobroma cacao L.）

Preliminary research results indicated that the stomata is one important trait that can be used as an indicator of resistance to vascular streak dieback （VSD） disease. The influence of genotype and environment on the stomatal characters is expected to provide information for specificlocations （habitats） suitable for planting cocoa in particular to avoid VSD attack. The research was conducted at KendengLembu, PTPNXII, East Java. Experimental design used a splitplot design testing： location （altitude） and genotype factors. The location factors, distinguished on the basis of the altitude, were labelled highlands and lowlands. The genotype factors consisted of three clones with different levels of resistance to VSD diseases： PA 191 （tolerant）, BL 703 and GC 29 （susceptible）. The cocoa clones observed were top grafted onto locally available rootstock seedling and planted in 2006-2007. The maintenance of the plants was conducted in accordance with the standards of cocoa cultivation in the PTPN XII. Parameters measured were leaf stomata traits at different positions of the leaf （tip, middle and base）. Characters observed were the number of stomata, opening width of stomata, and diameter of the stomata. The results of the research showed that PA 191 in the lowlands had the lowest number, diameter and opening width of stomata. In contrast, GC 29 in the lowlands showed the highest number of stomata PA 191 and BL 703 in the highlands had a number, diameter and openings width of stomata that was relatively low compared with GC 29. However, the characters of the stomata （number, diameter and openings width of stomata） of the three genotypes in the highland showed a smaller value in each case than in the lowlands. The severity level of VSD attack was greater in the lowlands than in the highlands and PA 191 showed the lowest level of VSD attack at both altitudes.

Overexpression of tonoplast Ca^(2+)-ATPase in guard cells synergistically enhances stomatal opening and drought tolerance

Stomata play a crucial role in plants by controlling water status and responding to drought stress.However,simultaneously improving stomatal opening and drought tolerance has proven to be a significant challenge.To address this issue,we employed the OnGuard quantitative model,which accurately represents the mechanics and coordination of ion transporters in guard cells.With the guidance of OnGuard,we successfully engineered plants that overexpressed the main tonoplast Ca^(2+)-ATPase gene,ACA11,which promotes stomatal opening and enhances plant growth.Surprisingly,these transgenic plants also exhibited improved drought tolerance due to reduced water loss through their stomata.Again,OnGuard assisted us in understanding the mechanism behind the unexpected stomatal behaviors observed in the ACA11 overexpressing plants.Our study revealed that the overexpression of ACA11 facilitated the accumulation of Ca^(2+)in the vacuole,thereby influencing Ca^(2+)storage and leading to an enhanced Ca^(2+)elevation in response to abscisic acid.This regulatory cascade finely tunes stomatal responses,ultimately leading to enhanced drought tolerance.Our findings underscore the importance of tonoplast Ca^(2+)-ATPase in manipulating stomatal behavior and improving drought tolerance.Furthermore,these results highlight the diverse functions of tonoplast-localized ACA11 in response to different conditions,emphasizing its potential for future applications in plant enhancement.

Water Responsive Fabrics with Artificial Leaf Stomata

Due to fiber swelling,textile fabrics containing hygroscopic fibers tend to decrease pore size under wet or increasing humid-ity and moisture conditions,the reverse being true.Nevertheless,for personal thermal regulation and comfort,the opposite is desirable,namely,increasing the fabric pore size under increasing humid and sweating conditions for enhanced ventila-tion and cooling,and a decreased pore size under cold and dry conditions for heat retention.This paper describes a novel approach to create such an unconventional fabric by emulating the structure of the plant leaf stomata by designing a water responsive polymer system in which the fabric pores increase in size when wet and decrease in size when dry.The new fabric increases its moisture permeability over 50%under wet conditions.Such a water responsive fabric can find various applications including smart functional clothing and sportswear.

Stomatal Density and Bio-water Saving

Bio-water saving is to increase water use efficiency of crops or crop yield per unit of water input. Plant water use efficiency is determined by photosynthesis and transpiration, for both of which stomata are crucial. Stomata are pores on leaf epidermis for both water and carbon dioxide fluxes that are controlled by two major factors： stomatal behavior and density. Stomatal behavior has been the focus of intensive research, while less attention has been paid to stomatal density. Recently, a number of genes controlling stomatal development have been identified. This review summarizes the recent progress on the genes regulating stomatal density, and discusses the role of stomatal density in plant water use efficiency and the possibility to increase plant water use efficiency, hence bio-water saving by genetically manipulating stomatal density.

The evolution and diurnal expression patterns of photosynthetic pathway genes of the invasive alien weed,Mikania micrantha

Mikania micrantha is a fast-growing global invasive weed species that causes severe damage to natural ecosystems and very large economic losses of forest and crop production.It has advantages in photosynthesis,including a similar net photosynthetic rate as C4 plants and a higher carbon fixation capacity.We used a combination of genomics and transcriptomics approaches to study the evolutionary mechanisms and circadian expression patterns of M.micrantha.In M.micrantha,16 positive selection genes focused on photoreaction and utilization of photoassimilates.In different tissues,98.1%of the genes associated with photoresponse had high expression in stems,and more than half of the genes of the C4 cycle had higher expression in stems than in leaves.In stomatal opening and closing,2 genes of carbonic anhydrase(CAs)had higher expression at 18:00 than at 8:00,and the slow anion channel 1(SLAC1)and high-leaf-temperature 1 kinase(HT1)genes were expressed at low levels at 18:00.In addition,genes associated with photosynthesis had higher expression levels at 7:00 and 17:00.We hypothesized that M.micrantha may undergo photosynthesis in the stem and flower organs and that some stomata of the leaves were opening at night by CO_(2)signals.In addition,its evolution may attenuate photoinhibition at high light intensities,and enhance more efficient of photosynthesis during low light intensity.And the tissue-specific photosynthetic types and different diurnal pattern of photosynthetic-related genes may contribute to its rapid colonization of new habitats of M.micrantha.

A polygalacturonase gene OsPG1 modulates water homeostasis in rice

A dynamic plant architecture is the basis of plant adaptation to changing environments.Although many genes regulating leaf rolling have been identified,genes directly associated with water homeostasis are largely unknown.Here,we isolated a rice mutant,dynamic leaf rolling 1(dlr1),characterized by‘leaf unfolding in the morning-leaf rolling at noon-leaf unfolding in the evening’during a sunny day.Water content was decreased in rolled leaves and water sprayed on leaves caused reopening,indicating that in vivo water deficiency induced the leaf rolling.Map-based cloning and expression tests demonstrated that an A1400G single base mutation in Oryza sativa Polygalacturonase 1(OsPG1)/PHOTO-SENSITIVE LEAF ROLLING 1(PSL1)was responsible for the dynamic leaf rolling phenotype in the dlr1 mutant.OsPG1 encodes a polygalacturonase,one of the main enzymes that degrade demethylesterified homogalacturonans in plant cell walls.OsPG1 was constitutively expressed in various tissues and was enriched in stomata.Mutants of the OsPG1 gene exhibited defects in stomatal closure and decreased stomatal density,leading to reduced transpiration and excessive water loss under specific conditions,but had normal root development.Further analysis revealed that mutation of OsPG1 led to reduced pectinase activity in the leaves and increased demethylesterified homogalacturonans in guard cells.Our findings reveal a mechanism by which OsPG1 modulates water homeostasis to control dynamic leaf rolling,providing insights for plants to adapt to environmental variation.

大田和旱棚环境下小麦旗叶气孔性状变异及其与光合参数的关系

为了明确小麦旗叶与气孔性状的变异及其对干旱胁迫的响应,在大田和旱棚环境下种植204个小麦品种,测定其旗叶和气孔性状,并对10份气孔性状极端的材料的光合参数进行测定分析。结果表明,小麦品种间旗叶和气孔性状存在显著差异,在旱棚环境下旗叶长度、旗叶面积、气孔长度和气孔面积较大田分别降低了6.6%、7.0%、1.4%和3.0%,气孔密度增加了12.0%。旗叶长度与气孔长度、旗叶宽度与气孔宽度和旗叶面积与气孔面积的相关系数在大田环境下分别为0.18、0.15和0.18,在旱棚环境下分别为0.31、0.18和0.25。极端材料中,与气孔密度大的材料相比,气孔密度小的材料的净光合速率在大田环境下增大了9.67%,蒸腾速率增加27.57%,瞬时水分利用效率减少26.04%。在大田环境下气孔长度与蒸腾速率和气孔导度均呈正相关(相关系数均为0.37),气孔面积与蒸腾速率呈正相关(相关系数为0.39),气孔密度与蒸腾速率和净光合速率均呈负相关(相关系数均为-0.38);在旱棚环境下气孔长度与蒸腾速率和净光合速率均呈正相关(相关系数分别为0.36和0.42)。这说明,环境条件对小麦旗叶性状之间的相关性影响较大,较大的旗叶面积和较低的气孔密度会促进小麦光合作用,有利于提高小麦的产量及抗旱性。

基于叶片形态及显微特征评价12个猕猴桃栽培品种的抗旱性

【目的】探讨不同猕猴桃品种的叶片宏观形态和微观结构特征的差异,筛选抗旱性评价关键指标并进行抗旱性综合评价。【方法】采用多功能图像分析法、石蜡切片法和扫描电镜技术,选取12个猕猴桃栽培品种为材料,对叶片形态、气孔器和表皮毛微特征、解剖结构等24项指标进行观测、记录。通过方差分析明确不同品种的叶片形态和解剖结构的差异,以主成分分析筛选综合指标,运用隶属函数法进行抗旱性综合评价。【结果】不同猕猴桃品种的叶片形态、解剖结构、气孔器及表皮毛特征具有显著差异,相关性分析表明不同指标间具有显著或极显著的相关性,运用主成分分析从24个抗旱相关指标中筛选了叶片宽度、叶形指数、气孔长轴、单簇茸毛数、上表皮细胞厚度、下表皮细胞厚度、栅海比、组织结构紧密度共8项关键性指标。通过隶属函数法比较不同品种间的抗旱能力,抗旱性强弱为:徐香>金美>金霞>海沃德>金艳>金魁>金梅>东红>翠玉>金桃>桂海4号>Hort16A。使用聚类分析将12个猕猴桃品种按抗旱能力聚为5类。【结论】通过对叶片形态及显微结构的分析,评价并筛选到抗旱性相对较强的猕猴桃品种,研究结果为猕猴桃品种改良、品种选择及生产管理等提供了基础理论依据。

GID1 modulates stomatal response and submergence tolerance involving abscisic acid and gibberellic acid signaling in rice

Plant responses to abiotic stresses are coordinated by arrays of growth and developmental programs. Gibberellic acid （GA） and abscisic acid （ABA） play critical roles in the developmental programs and environmental responses, respectively, through complex signaling and metabolism networks. However, crosstalk between the two phytohormones in stress responses remains largely unknown. In this study, we report that GIBBERELLIN-INSENSITIVE DWARF 1 （GID1）, a soluble receptor for GA, regulates stomata[ develop- ment and patterning in rice （Oryza sativa L.）. The gidl mutant showed impaired biosynthesis of endogenous ABA under drought stress conditions, but it exhibited enhanced sensi- tivity to exogenous ABA. Scanning electron microscope and infrared thermal image analysis indicated an increase in the stomatal conductance in the gidl mutant under drought conditions. Interestingly, the gidl mutant had increased levels of chlorophyll and carbohydrates under submergence conditions, and showed enhanced reactive oxygen species （ROS）-scavenging ability and submergence tolerance compared with the wild-type. Further analyses suggested that the function of GID1 in submergence responses is partially dependent on ABA, and GA signaling by GID1 is involved in submergence tolerance by modulating carbohydrate consumption. Taken together, these findings suggest GID1 plays distinct roles in stomatal response and submergence tolerance through both the ABA and GA signaling pathways in rice.

Carbon Monoxide-induced Stomatal Closure Involves Generation of Hydrogen Peroxide in Vicia faba Guard Cells

Here the regulatory role of CO during stomatal movement in Vicia faba L. was surveyed. Results indicated that, like hydrogen peroxide （H2O2）, CO donor HemaUn induced stomatal closure in dose- and time-dependent manners. These responses were also proven by the addition of gaseous CO aqueous solution with different concentrations, showing the first time that CO and H2O2 exhibit the similar regulation role in the stomatal movement. Moreover, our data showed that ascorbic acid （ASA, an important reducing substrate for H2O2 removal） and diphenylene iodonium （DPI, an inhibitor of the H2O2-generating enzyme NADPH oxidase） not only reversed stomatal closure by CO, but also suppressed the H2O2 fluorescence induced by CO, implying that CO induced-stomatal closure probably involves H2O2 signal. Additionally, the CO/NO scavenger hemoglobin （Hb） and CO specific synthetic inhibitor ZnPPIX, ASA and DPI reversed the darkness-induced stomatal closure and H2O2 fluorescence. These results show that, perhaps like H2O2, the levels of CO in guard cells of V. faba are higher in the dark than in light, HO-1 and NADPH oxidase are the enzyme systems responsible for generating endogenous CO and H2O2 in darkness respectively, and that CO is involved in darkness-induced H2O2 synthesis in V. faba guard cells.

Phosphorylation of Serine 186 of bHLH Transcription Factor SPEECHLESS Promotes Stomatal Development in Arabidopsis

The initiation of stomatal lineage and subsequent asymmetric divisions in Arabidopsis require the activity of the basic helix-loop-helix transcription factor SPEECHLESS （SPCH）. It has been shown that SPCH controls entry into the stomatal lineage as a substrate either of the MITOGEN-ACTIVATED PROTEIN KINASE （MAPK） cascade or GSK3-1ike kinase BRASSlNOSTEROID INSENSITIVE 2 （BIN2）. Here we show that three serine residues of SPCH appear to be the primary phosphorylation targets of Cyclin-Dependent Kinases A;1 （CDKA;1） in vitro, and among them Serine 186 plays a crucial role in stomatal formation. Expression of an SPCH construct harboring a mutation that results in phosphorylation deficiencies on Serine 186 residue failed to rescue stomatal defects in spch null mutants. Expression of a phosphorylation-mimic mutant SPCHS186D complemented stomatal production defects in the transgenic lines harboring the targeted expression of dominant-negative CDKA;1.N146. Therefore, in addition to MAPK- and BIN2-mediated phos- phorylation on SPCH, phosphorylation at Serine 186 is positively required for SPCH function in regulating stomatal development.

A Sophisticated Network of Signaling Pathways Regulates Stomatal Defenses to Bacterial Pathogens

Guard cells are specialized cells forming stomatal pores at the leaf surface for gas exchanges between the plant and the atmosphere. Stomata have been shown to playan important role in plant defense as a part of the innate immune response. Plants actively close their stomata upon contact with microbes, thereby preventing pathogen entry into the leaves and the subsequent colonization of host tissues. In this review, we present current knowledge of molecular mechanisms and signaling pathways implicated in stomatal defenses, with particular emphasis on plant-bacteria interactions. Stomatal defense responses begin from the perception of pathogen-associated molecular patterns （PAMPs） and activate a signaling cascade involving the production of secondary messengers such as reactive oxygen species, nitric oxide, and calcium for the regulation of plasma membrane ion channels. The analyses on downstream molecular mechanisms implicated in PAMP-triggered stomatal closure have revealed extensive interplays among the components regulating hormonal signaling pathways. We also discuss the strategies deployed by pathogenic bacteria to counteract stomatal immunity through the example of the phytotoxin coronatine.

山桐子雌、雄株叶片表皮微形态特征比较

【目的】探究山桐子叶片表皮微形态特征及其雌、雄株差异,为该种质资源的挖掘利用提供参考。【方法】利用扫描电镜对40份山桐子(雌、雄株各半)叶片进行微形态观察,测定12个气孔相关性状,并分析样品间的异同。【结果】(1)山桐子雌、雄株叶片的表皮毛、细胞形态、气孔特征及蜡质式样相似,其下表皮密布的类锥形纤维体型蜡质纹饰,鲜见于其他植物类群。(2)山桐子雌株叶片的气孔大小(长度、宽度、面积及周长)及密度相关参数均略大于雄株;雄株叶片的气孔开口相关参数(孔隙宽度、开口面积及气孔开度)均略高于雌株;但所有差异均未达到统计学显著水平(P>0.05)。(3)多数气孔性状彼此显著相关,而气孔密度与其他性状关联较弱,可能受到相对独立的遗传调控。【结论】研究明确了山桐子叶片表皮的微形态特征,其类锥形纤维体型蜡质式样可作为种质评鉴的关键依据,其气孔性状参数可为童期种苗的性别判定提供重要参考。

YODA-HSP90 Module Regulates Phosphorylation-Dependent Inactivation of SPEECHLESS to Control Stomatal Development under Acute Heat Stress in Arabidopsis

Stomatal ontogenesis,patterning,and function are hallmarks of environmental plant adaptation,especially to conditions limiting plant growth,such as elevated temperatures and reduced water availability.The specification and distribution of a stomatal cell lineage and its terminal differentiation into guard cells require a master regulatory protein phosphorylation cascade involving the YODA mitogen-activated protein kinase kinase kinase.YODA signaling results in the activation of MITOGEN-ACTIVATED PROTEIN KINASEs(MPK3 and MPK6),which regulate transcription factors,including SPEECHLESS(SPCH).Here,we report that acute heat stress affects the phosphorylation and deactivation of SPCH and modulates stomatal density.By using complem entary molecular,genetic,biochemical,and cell biology approaches,we provide solid evidence that HEAT SHOCK PROTEINS 90(HSP90s)play a crucial role in transducing heat-stress response through the YODA cascade.Genetic studies revealed that YODA and HSP90.1 are epistatic,and they likely function linearly in the same developmental pathway regulating stomata formation.HSP90s interact with YODA,affectits cellular polarization,and modulate the phosphorylation of downstream targets,such as MPK6 and SPCH,under both normal and heat-stress conditions.Thus,HSP90-mediated specification and differentiation of the stomatal cell lineage couples stomatal development to environmental cues,providing an adaptive heat stress response mechanism in plants.

Light-Regulated Stomatal Aperture in Arabidopsis

The stomatal pores of plant leaves, situated in the epidermis and surrounded by a pair of guard cells, allow CO2 uptake for photosynthesis and water loss through transpiration. Blue light is one of the dominant environmental signals that control stomatal movements in leaves of plants in a natural environment. This blue light response is mediated by blue/UV A light-absorbing phototropins （phots） and cryptochromes （crys）. Red/far-red light-absorbing phytochromes （phys） also play a role in the control of stomatal aperture. The signaling components that link the perception of light signals to the stomatal opening response are largely unknown. This review discusses a few newly discovered nuclear genes, their function with respect to the phot-, cry-, and phy-mediated signal transduction cascades, and possible involve- ment of circadian clock.