Genetic variation of stomatal conductance, blue light sensitivity and zeaxanthin content in guard cells of Pima cotton (Gossypium barbadense)

Pima S‐6 ( Gossypium barbadense L.) is a modern line with high stomatal conductance, while B368 is a primitive cotton with low conductance. The blue light sensitivity of adaxial guard cells, probed as the blue light‐dependent enhancement of the red light‐induced chlorophyll a fluorescence quenching, was investigated in these two cotton lines with contrasting stomatal conductance. Adaxial guard cells isolated from Pima S‐6 cotton plants had a significantly higher carotenoid content and a higher blue light sensitivity than those isolated from B368 plants. In a growth chamber‐grown F₂ population of a cross between these two lines, adaxial stomatal conductances of individual plants segregated over a range exceeding the average conductances of the parents. Carotenoid content and the blue light sensitivity of adaxial guard cells also segregated. The concentrations of xanthophylls and β‐carotene in the adaxial guard cells were poorly correlated with the blue light response, except for zeaxanthin. The co‐segregation of stomatal conductance and blue light sensitivity suggested that the stomatal response to blue light may play a role in the regulation of stomatal conductance in the intact leaf. Zeaxanthin content and blue light sensitivity also co‐segregated, suggesting that both parameters are under genetic control. The co‐segregation of zeaxanthin content, blue light sensitivity and stomatal conductance provides further evidence for a role of zeaxanthin in the blue light photoreception of guard cells.     

Abaxial and adaxial stomata from Pima cotton (Gossypium barbadense L.) differ in their pigment content and sensitivity to light quality

Sensitivity to light quality and pigment composition were analysed and compared in abaxial and adaxial stomata of Gossypium barbadense L. (Pima cotton). In most plants, abaxial (lower) stomatal conductances are higher than adaxial (upper) ones, and stomatal opening is more sensitive to blue light than to red. In greenhouse-grown Pima cotton, abaxial stomatal conductances were two to three times higher than adaxial ones. In contrast, adaxial stomatal conductances were 1·5 to two times higher than abaxial ones in leaves from growth chamber-grown plants. To establish whether light quality was a factor in the regulation of the relationship between abaxial and adaxial stomatal conductances, growth-chamber-grown plants were exposed to solar radiation outdoors and to increased red light in the growth chamber. In both cases, the ratios of adaxial to abaxial stomatal conductance reverted to those typical of greenhouse plants. We investigated the hypothesis that adaxial stomata are more sensitive to blue light and abaxial stomata are more sensitive to red light. Measurements of stomatal apertures in mechanically isolated epidermal peels from growth chamber and greenhouse plants showed that adaxial stomata opened more under blue light than under red light, while abaxial stomata had the opposite response. Using HPLC, we quantified the chlorophylls and carotenoids extracted from isolated adaxial and abaxial guard cells. All pigments analysed were more abundant in the adaxial than in the abaxial guard cells. Antheraxanthin and β-carotene contents were 2·3 times higher in adaxial than in abaxial guard cells, comparing with ad/ab ratios of 1·5–1·9 for the other pigments. We conclude that adaxial and abaxial stomata from Pima cotton have a differential sensitivity to light quality and their distinct responses are correlated with different pigment content.     

27种木犀属植物叶表皮微形态特征的研究

利用光学显微镜和扫描电子显微镜观察了27种木犀属植物的叶表皮,测量并统计了气孔器类型、气孔大小、气孔密度、气孔指数及腺点密度等指标,以明确各种的叶表皮细胞形状及垂周壁式样、表皮角质膜、蜡质纹饰及气孔外拱盖的具体特征。结果显示:木犀属植物叶下表皮有气孔器,形状为圆形、椭圆形;气孔器类型多为不规则型,只有总状桂花和狭叶木犀为环列型;气孔器外围角质层有放射状、条状、环状、颗粒状等多种类型;叶表皮细胞形状有无规则形和多边形2种;下表皮腺点的数目远远大于上表皮。研究表明,木犀属植物气孔器和叶表皮细胞特征在种之间差异比较明显,可以作为种间鉴定的重要依据,具有重要的分类学意义。     

毛茛科铁线莲属的叶表皮特征及其系统学意义(英文)

用光学显微镜和扫描电镜 ,较全面地观察了铁线莲属 (Clematis)植物和邻近类群的叶表皮特征 ,并对其系统学意义进行了讨论。在光学显微镜下 ,观察了铁线莲属 12组 6 3种 5变种及其同族邻近类群 3属 9种 ;在扫描电镜下 ,观察了铁线莲属 7组 2 7种 2变种及其邻近类群 2属 6种植物的成熟叶表皮细胞及气孔器的特征。在光学显微镜下可见 :叶表皮细胞形状 (表面观 )为多边形、不规则形 ,垂周壁式样为较平直、浅波状和波状 ,气孔器普遍存在于下表皮 ,少数种的上表皮也有分布 ,其类型均为无规则型。在扫描电镜下可见 :叶片通常具有条纹或有颗粒状或鳞片状附属物 ,气孔器外拱盖内缘通常为浅波状或近平滑。在黄花铁线莲组 (sect.Meclatis (Spach)Tamura)和灌木铁线莲组 (sect.FruticellaTamura)中 ,叶表皮具有双面气孔器的特征对于组下亚组的划分有一定意义。并且叶表皮特征对于一些种的分类学处理也有一定的价值 ,同时也为属下组间的系统进化关系提供了一些线索     

Light Saturation of Stomatal Opening on the Adaxial and Abaxial Epidermis of Commelina communis

The responses of adaxial and abaxial stomata to light were examinedon detached epidermis of Commelina communis. Stomata on theabaxial epidermis were considerably more sensitive to lightthan those on the adaxial epidermis, supporting the view thatthe differences in photosensitivity are inherent rather thanthe result of differences in the microenvironment within theleaf. The sensitivity of adaxial and abaxial stomata to bluelight was also examined. The quantum flux received by a pairof guard cells appears to be sufficient to support a directeffect of blue light on ion transport into the guard cells,but there is no evidence to suggest that blue light is essentialfor stomatal opening.     

Photocontrol of the Functional Coupling between Photosynthesis and Stomatal Conductance in the Intact Leaf : Blue Light and Par-Dependent Photosystems in Guard Cells

The photocontrol of the functional coupling between photosynthesis and stomatal conductance in the leaf was investigated in gas exchange experiments using monochromatic light provided by lasers. Net photosynthesis and stomatal conductance were measured in attached leaves of Malva parviflora L. as a function of photon irradiance at 457.9 and 640.0 nanometers.

Photosynthetic rates and quantum yields of photosynthesis were higher under red light than under blue, on an absorbed or incident basis.

Stomatal conductance was higher under blue than under red light at all intensities. Based on a calculated apparent photon efficiency of conductance, blue and red light had similar effects on conductance at intensities higher than 0.02 millimoles per square meter per second, but blue light was several-fold more efficient at very low photon irradiances. Red light had no effect on conductance at photon irradiances below 0.02 millimoles per square meter per second. These observations support the hypothesis that stomatal conductance is modulated by two photosystems: a blue light-dependent one, driving stomatal opening at low light intensities and a photosynthetically active radiation (PAR)-dependent one operating at higher irradiances.

When low intensity blue light was used to illuminate a leaf already irradiated with high intensity, 640 nanometers light, the leaf exhibited substantial increases in stomatal conductance. Net photosynthesis changed only slightly. Additional far-red light increased net photosynthesis without affecting stomatal conductance. These observations indicate that under conditions where the PAR-dependent system is driven by high intensity red light, the blue light-dependent system has an additive effect on stomatal conductance.

The wavelength dependence of photosynthesis and stomatal conductance demonstrates that these processes are not obligatorily coupled and can be controlled by light, independent of prevailing levels of intercellular CO₂. The blue light-dependent system in the guard cells may function as a specific light sensor while the PAR-dependent system supplies a CO₂-modulated energy source providing functional coupling between the guard cells and the photosynthesizing mesophyll.

     

Ontogenetic changes in stomatal size and conductance of sunflowers

The ontogenetic changes in stomatal size, frequency and conductance (g_s) on abaxial and adaxial leaf surfaces of sunflower plants (Helianthus annuus L. Russian Mammoth) were examined under controlled environmental conditions. The stomatal frequency on the adaxial and abaxial leaf surfaces decreased with leaf ontogeny and insertion level. The ratio of adaxial to abaxial stomatal frequency did not change with leaf ontogeny and insertion level, and 42–44% of total stomata was apportioned to the adaxial surface. Ontogenetic changes in stomatal pore length were detected and increased with ontogenesis. The stomatal length of both leaf surfaces had linear relationships with leaf area. Ontogenetic changes in g_s were similar between the two surfaces. However the adaxial g_s was lower than abaxial g_s in leaves of higher insertion levels. Conductance had a linear relationship with width x frequency but not with pore area.     

Distinct light responses of the adaxial and abaxial stomata in intact leaves of Helianthus annuus L

Using a laboratory-constructed system that can measure the gas exchange rates of two leaf surfaces separately, the light responses of the adaxial and abaxial stomata in intact leaves of sunflower ( Helianthus annuus L.) were investigated, keeping the intercellular CO₂ concentration ( C _i) at 300  µ L L⁻¹. When evenly illuminating both sides of the leaf, the stomatal conductance ( g _s) of the abaxial surface was higher than that of the adaxial surface at any light intensity. When each surface of the leaf was illuminated separately, both the adaxial and abaxial stomata were more sensitive to the light transmitted through the leaf (self-transmitted light) than to direct illumination. Relationships between the whole leaf photosynthetic rate ( A _n) and the g _s for each side highlighted a strong dependence of stomatal opening on mesophyll photosynthesis. Light transmitted through another leaf was more effective than the direct white light for the abaxial stomata, but not for the adaxial stomata. Moreover, green monochromatic light induced an opening of the abaxial stomata, but not of the adaxial stomata. As the proportion of blue light in the transmitted light is less than that in the white light, there may be some uncharacterized light responses, which are responsible for the opening of the abaxial stomata by the transmitted, green light.     

Stomatal function,density and pattern,and CO2 assimilation in Arabidopsis thaliana tmm1 and sdd1‐1 mutants

• Stomata modulate the exchange of water and CO₂ between plant and atmosphere. Although stomatal density is known to affect CO₂ diffusion into the leaf and thus photosynthetic rate, the effect of stomatal density and patterning on CO₂ assimilation is not fully understood.
• We used wild types Col‐0 and C24 and stomatal mutants sdd1‐1 and tmm1 of Arabidopsis thaliana, differing in stomatal density and pattern, to study the effects of these variations on both stomatal and mesophyll conductance and CO₂ assimilation rate. Anatomical parameters of stomata, leaf temperature and carbon isotope discrimination were also assessed.
• Our results indicate that increased stomatal density enhanced stomatal conductance in sdd1‐1 plants, with no effect on photosynthesis, due to both unchanged photosynthetic capacity and decreased mesophyll conductance. Clustering (abnormal patterning formed by clusters of two or more stomata) and a highly unequal distribution of stomata between the adaxial and abaxial leaf sides in tmm1 mutants also had no effect on photosynthesis.
• Except at very high stomatal densities, stomatal conductance and water loss were proportional to stomatal density. Stomatal formation in clusters reduced stomatal dynamics and their operational range as well as the efficiency of CO₂ transport.

     

Metabolic energy for stomatal opening. Roles of photophosphorylation and oxidative phosphorylation

The supply of energy for stomatal opening was investigated with epidermal peels of Commelina communis L. and Vicia faba L., under white, blue and red irradiation or in darkness. Fluencerate response curves of stomatal opening under blue and red light were consistent with the operation of two photosystems, one dependent on photosynthetic active radiation (PAR) and the other on blue light, in the guard cells. The PAR-dependent system was 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-sensitive and KCN-resistant and showed a relatively high threshold irradiance for its activation; its activity was most prominent at moderate to high irradiances. The blue-light-dependent photosystem was KCN-sensitive, was active at low irradiances, and interacted with the PAR-dependent photosystem at high blue irradiances. Stomatal opening in darkness, caused by CO₂-free air, fusicoccin or high KCl concentrations, was KCN-sensitive and DCMU-resistant. These data indicate that stomatal opening in darkness depends on oxidative phosphorylation for the supply of high-energy equivalents driving proton extrusion. Light-dependent stomatal opening appears to require photophosphorylation from guard-cell chloroplasts and the activation of the blue-light photosystem which could rely either on oxidative phosphorylation or a specific, membrane-bound electron-transport carrier.Abbreviations DCMU 3(3,4-dichlorophenyl)-1-1-dimethylurea - FC fusicoccin - KCN potassium cyanide - PAR photosynthetic active radiation - WL white light     

The effect of blue light on stomatal oscillations and leaf turgor pressure in banana leaves

Stomatal oscillations are cyclic opening and closing of stomata, presumed to initiate from hydraulic mismatch between leaf water supply and transpiration rate. To test this assumption, mismatches between water supply and transpiration were induced using manipulations of vapour pressure deficit (VPD) and light spectrum in banana (Musa acuminata). Simultaneous measurements of gas exchange with changes in leaf turgor pressure were used to describe the hydraulic mismatches. An increase of VPD above a certain threshold caused stomatal oscillations with variable amplitudes. Oscillations in leaf turgor pressure were synchronized with stomatal oscillations and balanced only when transpiration equaled water supply. Surprisingly, changing the light spectrum from red and blue to red alone at constant VPD also induced stomatal oscillations – while the addition of blue (10%) to red light only ended oscillations. Blue light is known to induce stomatal opening and thus should increase the hydraulic mismatch, reduce the VPD threshold for oscillations and increase the oscillation amplitude. Unexpectedly, blue light reduced oscillation amplitude, increased VPD threshold and reduced turgor pressure loss. These results suggest that additionally, to the known effect of blue light on the hydroactive opening response of stomata, it can also effect stomatal movement by increased xylem–epidermis water supply.     

Association genetics,geography and ecophysiology link stomatal patterning in Populus trichocarpa with carbon gain and disease resistance trade‐offs

Stomata are essential for diffusive entry of gases to support photosynthesis, but may also expose internal leaf tissues to pathogens. To uncover trade‐offs in range‐wide adaptation relating to stomata, we investigated the underlying genetics of stomatal traits and linked variability in these traits with geoclimate, ecophysiology, condensed foliar tannins and pathogen susceptibility in black cottonwood (Populus trichocarpa). Upper (adaxial) and lower (abaxial) leaf stomatal traits were measured from 454 accessions collected throughout much of the species range. We calculated broad‐sense heritability (H²) of stomatal traits and, using SNP data from a 34K Populus SNP array, performed a genome‐wide association studies (GWAS) to uncover genes underlying stomatal trait variation. H² values for stomatal traits were moderate (average H² = 0.33). GWAS identified genes associated primarily with adaxial stomata, including polarity genes (PHABULOSA), stomatal development genes (BRASSINOSTEROID‐INSENSITIVE 2) and disease/wound‐response genes (GLUTAMATE‐CYSTEINE LIGASE). Stomatal traits correlated with latitude, gas exchange, condensed tannins and leaf rust (Melampsora) infection. Latitudinal trends of greater adaxial stomata numbers and guard cell pore size corresponded with higher stomatal conductance (g_s) and photosynthesis (A_max), faster shoot elongation, lower foliar tannins and greater Melampsora susceptibility. This suggests an evolutionary trade‐off related to differing selection pressures across the species range. In northern environments, more adaxial stomata and larger pore sizes reflect selection for rapid carbon gain and growth. By contrast, southern genotypes have fewer adaxial stomata, smaller pore sizes and higher levels of condensed tannins, possibly linked to greater pressure from natural leaf pathogens, which are less significant in northern ecosystems.     

Relationship between stomatal frequencies,yield components and morphological characters in collections of winter wheat cultivars

Genotypes on the Belgian national list as well as about 120 genotypes of winter wheat from the world collection were examined for the relationships of their stomatal frequencies in the flag leaf with yield, yield components and other morphological characters. Stomata were in rows, with a higher density in adaxial leaf surface. Cultivars differed significantly in both stomatal density and number of rows of stomata per unit of leaf width. Yield and morphological characters in general showed no significant correlation with stomatal frequencies. Densities in all series examined ranged from 46 to 78 stomata per mm² in the adaxial leaf epidermis and from 32 to 93 in the abaxial one.     

盾叶秋海棠叶表皮气孔簇的发育及分布格局

气孔是植物控制气体交换和调节水分散失的门户。大部分高等植物气孔的分布格局是相邻气孔之间被一至多个表皮细胞所间隔。而在有限分布的几个科属的植物种中发现气孔成簇分布的现象 ,即由 2至多个紧密相邻的气孔器组成相对独立的单元 ,称为气孔簇 (stomatalcluster)。以中国原产的盾叶秋海棠 (BegoniapeltatifoliaLi)为研究对象 ,探讨了叶表皮气孔簇的发育机制及其分布格局。结果表明 :气孔发育初期 ,气孔拟分生组织的成簇 (相邻紧密 )排列可能是气孔簇形成的主要机制 ;气孔副卫细胞恢复分裂形成的卫星拟分生组织也对气孔簇的形成起一定的作用。把气孔簇和单个气孔视为一个气孔单元发现 ,盾叶秋海棠气孔单元密度 (单位面积中气孔单元数 )和气孔单元大小 (气孔单元所包含气孔数 )在叶片上呈有规律的分布 :前者由叶片中部向叶尖、叶缘逐圈增多 ,而后者逐圈减少。对这种分布格局的成因进行了讨论     

Stomatal response of hybrid poplar to incident light, sudden darkening and leaf excision

Responses of abaxial and adaxial stomata of Populus trichocarpa Torr. & Gray. × P. deltoides Bartr. (ex Marsh.) cv. Unal to incident light, sudden darkening and leaf excision in the light and in the dark were studied on 5-year-old trees in the field using diffusion porometry. Stomatal closure in the dark was found to be incomplete in most cases studies. Stomata closed after leaf excision in the dark within 90 min. Stomatal closure after darkening of an entire tree or an entire branch (white the rest of the tree was in the light) was slower, and complete stomatal closure was noticed only for adaxial stomata after 3 h. Adaxial stomata were more reactive and sensitive than abaxial stomata to sudden darkening and leaf excision in the light and the dark. In all treatments, stomatal response was more responsive in mature leaves than in young, still expanding leaves.     

Insertion Profiles in Stomatal Density and Sizes in Nicotiana Tabacum L. Plantlets

Tobacco (Nicotiana tabacum L. cv. Samsun) plantlets were cultured in vitro on Murashige-Skoog medium photoautotrophically (without sucrose) or photomixotrophically (with 3 % sucrose) under two irradiances [70 or 230 µmol m^–2 s^–1]. Significant differences in stomatal density and sizes in leaves of different insertion levels (3^rd, 5^th and 7^th leaves from bottom) in photomixotrophic plantlets but not in photoautotrophic ones were found after 35 d of culture. Stomatal density was higher in upper leaves and on abaxial leaf side. Higher irradiance enhanced stomatal density in photoautotrophic plantlets. Stomatal sizes decreased with leaf insertion level but no significant differences between leaf sides were found. Abaxial stomata were more circular than the adaxial ones. In photomixotrophic plantlets stomata tended to be more elongated in the 3^rd and the 5^th leaves, whereas stomatal elongation in photoautotrophic plantlets was similar in all leaves.     

Heterogeneity of stomatal density in the second wheat leaf

The stomatal density on abaxial epidermis of the second wheat(Triticum aestivum L.) leaf increased step by step from the leaf base to its tip. On adaxial epidermis, this increasing tendency was generally maintained, but close to both the base and the apex two maxima were determined. In the direction perpendicular to leaf length, maximum stomatal density was close to the edges, and minimum one was in the central part of the leaf blade.     

14种木犀榄族植物叶表皮微形态的研究

利用光学显微镜和扫描电子显微镜对木犀榄族（Oleeae）5属14种植物的叶表皮微形态特征进行了观察,结果表明：（1）叶表皮细胞形状有无规则形和多边形两种;下表皮腺点的数目远远大于上表皮,流苏树上表皮细胞没有腺点;叶下表皮有气孔器,形状为圆形、椭圆形;气孔器均为不规则型;气孔器外围角质层有放射状、条状、环状、颗粒状等多种类型;（2）气孔器和叶表皮细胞许多特征具有明显的种间差异,可以作为种间鉴定的重要依据;（3）叶表皮微形态结构上的许多共同特征,表明木犀榄族植物是单独一自然类群。上述特征可为木犀榄族植物属及物种的划分与鉴定、系统演化关系的探讨等提供参考。     

金星蕨科16种植物叶表皮特征的研究

利用光学显微镜对金星蕨科(Thelypteridaceae)8属16种植物的叶表皮形态进行了观察和研究,为金星蕨科植物的系统演化及分类提供科学依据。结果表明:(1)16种金星蕨科植物的叶片表皮细胞为不规则型,表皮细胞垂周壁大多呈深波状。(2)气孔为下生型,多呈椭圆形;共观察到6种气孔器类型(极细胞型、腋下细胞型、聚合极细胞型、聚腋下细胞型、不规则型和聚围绕细胞型),每种植物具2~5种不同类型的气孔器。(3)金星蕨科8属植物在表皮细胞大小、垂周壁形状、气孔大小和形状、气孔密度、气孔指数和气孔器类型上存在一定的属间差异。     

Asymmetric responses of adaxial and abaxial stomata to elevated CO2: impacts on the control of gas exchange by leaves

The response of adaxial and abaxial stomatal conductance in Rumex obtusifolius to growth at elevated atmospheric concentrations of CO₂ (250 μmol mol^?1 above ambient) was investigated over two growing seasons. The conductance of both the adaxial and abaxial leaf surfaces was found to be reduced by elevated concentrations of CO₂. Elevated CO₂ caused a much greater reduction in conductance for the adaxial surface than for the abaxial surface. The absence of effects upon stomatal density indicated that the reductions were probably the result of changes in stomatal aperture. Partitioning of gas exchange between the leaf surfaces revealed that increased concentrations of CO₂ caused increased rates of photosynthesis only via the abaxial surface. Additionally, leaf thickness was found to increase during growth at elevated concentrations of CO₂. The tendency for these amphistomatous leaves to develop a distribution of conductance approaching that of hypostomatous leaves clearly reduced their maximum photosynthetic potential. This conclusion was supported by measurements of stomatal limitation, which showed greater values for the adaxial surfaces, and greater values at elevated CO₂. This reduction in photosynthesis may in part be caused by higher diffusive limitations imposed because of increased leaf thickness. In an uncoupled canopy, asymmetrical stomatal responses of the kind identified here may appreciably reduce transpiration. Species which show symmetrical responses are less likely to show reduced transpirational rates, and a redistribution of water loss between species may occur. The implications of asymmetrical stomatal responses for photosynthesis and canopy transpiration are discussed.