Oscillations in stomatal conductance of hybrid poplar leaves in the light and dark

Cycling of stomatal conductance in three hybrid poplar ( Populus sp.) cultivars was observed under a variety of conditions. Illumination of plants kept previously in the dark induced very large oscillations with a period of about 40 min and large oscillations with a shorter period (< 10 min) were superimposed on the longer cycles. During these oscillations, large changes in conductance could occur very rapidly (1.0 cm s⁻¹ in 3 min). Plants in constant light also displayed both long and short term cycles in conductance, but these were smaller in amplitude than those induced by sudden illumination. Stomatal oscillations were also observed in darkness and after darkening of previously illuminated plants. These oscillations had shorter (< 30 min) and less regular periods than those observed in the light. Such cycling in the dark is rare. Cycling of the two leaf surfaces was sometimes in synchrony in the light, and more so after a perturbation. Little synchrony between the two surfaces was observed in the dark. Stomatal movements of different leaves on a plant were usually relatively independent. Transient stomatal opening occurred following leaf excision in the light or dark, and often after sudden darkening of intact leaves. Also, stomata of intact leaves sometimes transiently closed following illumination.     

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.     

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.     

Variation of Leaf Stomatal Conductance in Winter Wheat Canopy

Leaf stomatal conductance measured and analysed in the canopies of two winter wheat varieties in the field revealed that the probability of adaxial to abaxial conductance ratio followed an approximately normal distribution with a peake value of about 1.5. The ratio changed with the developmental stages being maximium at the heading stage. Leaf stomata in wheat of the upper part of the canopy were more active and showed more pronounced diurnal change of conductance than those of the lower part. Stomatal conductance decreased from top to bottom in canopy as a negative exponential function. By comparing adaxial and abaxial conductances in the apical, middle and basal parts of a leaf, the distribution of the stomatal conductances of a wheat leaf was as follows: a steady decrease from the basal part of adaxial, through the middle and apical parts of the adaxial surface turning to the apical part of abaxial, and then the middle and lastly, the basal part of abaxial. Based on values of the correlation coefficients among the various stomatal conductance and average stomatal conductance, the authors suggested that optimal apical measurement of stomatal conductance would be at the middle and apical parts and that of abaxial would be at middle and basal parts.     

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.     

冬小麦群体叶片气孔导度差异性分析

对冬小麦 (Triticum aestivum L.)两个品种 3个生育期测定和分析了群体叶片的气孔导度。结果表明 ,近轴面气孔导度比远轴面的大 ,二者之比呈近似正态分布 ,最大概率出现约为 1 .5,该比值在冠层垂直方向变化不显著 ,但随季节而变 ,抽穗期最大。叶片气孔导度从冠层顶部向下迅速递减 ,递减系数约为 0 .57,且各层日变化大致平行。冠层上部气孔活跃 ,导度日变化明显 ,下部日变化不大。同一叶片的气孔导度由近轴面的叶基 ,经由其叶中、叶尖 ,翻过尖点 ,再从远轴面的叶尖经叶中向叶基递减。对近轴面叶中、叶尖气孔导度与该面平均气孔导度相关系数较大 ,而对远轴面叶中、叶基气孔导度与该面气孔导度相关系数较大 ,据此建议测定近轴面气孔导度时 ,应以叶中、叶尖部位为最佳点 ,而测定远轴面气孔导度时 ,应以叶中、叶基部位为最佳点     

Kinetic characterization of reduced pyridine nucleotide dehydrogenases (duroquinone-dependent) in cucurbita microsomes

Stomatal conductances of normally oriented and inverted leaves were measured as light levels (photosynthetic photon flux densities) were increased to determine whether abaxial stomata of Vicia faba leaves were more sensitive to light than adaxial stomata. Light levels were increased over uniform populations of leaves of plants grown in an environmental chamber. Adaxial stomata of inverted leaves reached maximum water vapor conductances at a light level of 60 micromoles per square meter per second, the same light level at which abaxial stomata of normally oriented leaves reached maximum conductances. Abaxial stomata of inverted leaves reached maximum conductances at a light level of 500 micromoles per square meter per second, the same light level at which adaxial stomata of normally oriented leaves reached maximum conductances. Maximum conductances in both normally oriented and inverted leaves were about 200 millimoles per square meter per second for adaxial stomata and 330 millimoles per square meter per second for abaxial stomata. Regardless of whether leaves were normally oriented or inverted, when light levels were increased to values high enough that upper leaf surfaces reached maximum conductances (about 500 micromoles per square meter per second), light levels incident on lower, shaded leaf surfaces were just sufficient (about 60 micromoles per square meter per second) for stomata of those surfaces to reach maximum conductances. This `coordinated' stomatal opening on the separate epidermes resulted in total leaf conductances for normally oriented and inverted leaves that were the same at any given light level. We conclude that stomata in abaxial epidermes of intact Vicia leaves are not more sensitive to light than those in adaxial epidermes, and that stomata in leaves of this plant do not respond to light alone. Additional factors in bulk leaf tissue probably produce coordinated stomatal opening on upper and lower leaf epidermes to optimally meet photosynthetic requirements of the whole leaf for CO₂.     

Stomatal Diffusion Resistance of Snap Beans. II. Effect of Light

The effect of light on the stomatal resistance of abaxial and adaxial leaf surfaces of snap beans (Phaseolus vulgaris L.) was studied in the growth chamber and in the field. The adaxial stomata required more light to open than the abaxial stomata; the abaxial stomatal apertures were still about 50% open at 1% full sunlight and light-induced closure was never observed under daytime field conditions. A given value of abaxial stomatal resistance was obtained at a given illumination of the abaxial guard cells whether illumination was adaxial or abaxial.     

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.     

落羽杉属(杉科)叶表皮结构及气孔参数

落羽杉属Taxodium Rich.现生3种植物——落羽杉T. distichum (L.) Rich.、池杉T. ascendens Brongn.和墨西哥落羽杉T. mucronatum Tenore.的条形叶为双面气孔型或单面气孔型。叶片远轴面气孔分布于中脉两侧,每侧各有4-8列气孔。叶片中部气孔数量稳定,顶部和基部气孔数量比中部略少。近轴面气孔在中脉两侧各有1-4行,有时仅少数几个气孔或没有气孔分布。非气孔分布区内,表皮细胞长方形,细胞壁直或稍微呈波状,细胞长轴与叶片长轴一致。气孔分布区内的表皮细胞有时为多边形。气孔器椭圆形,长轴与叶片长轴垂直或成一定的角度。保卫细胞壁加厚明显,极端联合形成极层结构。落羽杉属3种现生植物的气孔密度和气孔指数差异显著,不同采集地的落羽杉气孔密度和气孔指数差异不显著。这3种植物的气孔指数的变异系数均小于气孔密度的变异系数,用气孔指数指示大气CO2浓度比用气孔密度可靠。     

Changes in water status during water stress at different stages of development in wheat

The dynamics of stomatal resistance and osmotic adjustment in response to plant water deficits and stage of physiological development was studied in the leaves of spring wheat ( Triticum aestivum L., GWO 1809). Plants were germinated and grown in pots in a growth chamber at the Duke University Phytotron to four physiological stages of development (4th leaf, 7th leaf, anthesis, and soft dough), during which time stomatal resistance, total water potential and osmotic potential were measured on the last fully developed leaf of water stressed and non-stressed plants. Pressure potential was obtained by difference. Stomatal closure of the abaxial and adaxial surfaces were independent of each other, each having a different critical total water potential. The total water potential required to close the stomata on the last fully developed leaf were different at different stages of physiological development, decreasing as the plants grew older. The development of osmoregulation in wheat allows the closure of stomata during the vegetative stage at a high total water potential, but insures that stomata remain open from anthesis through the ear filling period to a lower total water potential.     

小麦和玉米叶片两面气孔导性的差异及其与环境因素的关系

气孔是作物与大气进行水汽和CO_2交换的通道,当环境条件发生变化时,作物通过调节气孔的开度来控制叶片内部和外部的气体交换速率。作物群体中叶片两面的小生境有明显差异,在长期进化和适应中形成了两面气孔特性     

鸡蛋花(夹竹桃科)花表皮气孔的初步研究

对鸡蛋花花表皮的气孔进行初步研究,结果发现:花冠裂片的上表皮没有气孔的分布;花冠裂片的下表皮则有气孔的分布。当花冠裂片长度1.5cm时,气孔密度最大,且极显著地高于花冠裂片长度为2.0、2.5、3.5cm和4.0cm时的气孔密度。长度为3.0cm的花冠裂片的气孔指数最大,与花冠裂片长度为1.0、2.0、3.5cm和4.0cm时的气孔指数的差异均达极显著水平。在花冠筒长度为0.3cm和0.4cm时,没发现气孔;当花冠筒生长到0.5cm时开始出现气孔。花冠筒长度为0.6cm时,气孔密度最大,且极显著地高于其它长度花冠筒的气孔密度。花冠筒长为0.6、1.1cm和1.3cm时的气孔指数均极显著地大于长度为0.5cm花冠筒的气孔指数。花冠裂片和花冠筒下表皮的普通表皮细胞都呈不规则的多边形,保卫细胞呈半月形。     

麦田冠层气孔导度的分层研究

小麦灌浆期和乳熟期冠层各层叶片上、下表面的气孔导度之间呈正相关关系;冠层不同层的叶片气孔导度从早到傍晚有平行变化的趋势,数值上存在较大的差异,一般从冠层上到下递减。经分析,这主要与冠层叶片接受的光强自上而下递减有关,且这时所对应的叶片水势自冠层上到下递增的幅度大。测算结果表明,冠层气孔导度白天亦呈明显的日变化,灌浆期的值大于乳熟期的值。     

长春花叶片发育过程中气孔密度和气孔指数的动态变化

对长春花叶片近轴面和远轴面上的气孔密度和气孔指数在不同发育阶段的动态变化进行了研究.结果表明:在各个发育阶段,近轴面上的气孔以叶脉两侧居多,远轴面上的气孔则在整个叶片上均匀分布.将一个枝条上的10对真叶按发育顺序界定为10个发育阶段,即从枝条的顶端到基部,分别将第10、第9、第8……第1节位的叶片定义为第1、第2、第3...     

Early stomatal closure in waterlogged pea plants is mediated by abscisic acid in the absence of foliar water deficits

Abstract Soil waterlogging decreased leaf conductance (interpreted as stomatal closure) of vegetative pea plants (Pisuin sativum L. cv. ‘Sprite’) approximately 24 h after the start of flooding, i.e. from the beginning of the second 16 h-long photo-period. Both adaxial and abaxial surfaces of leaves of various ages and the stipules were affected. Stomatal closure was sustained for at least 3 d with no decrease in foliar hydration measured as water content per unit area, leaf water potential or leaf water saturation deficit. Instead, leaves became increasingly hydrated in association with slower transpiration. These changes in the waterlogged plants over 3 d were accompanied by up to 10-fold increases in the concentration of endogenous abscisic acid (ABA). Waterlogging also increased foliar hydration and ABA concentrations in the dark. Leaves detached from non-waterlogged plants and maintained in vials of water for up to 3 d behaved in a similar way to leaves on flooded plants, i.e. stomata closed in the absence of a water deficit but in association with increased ABA content. Applying ABA through the transpiration stream to freshly detached leaflets partially closed stomata within 15 min. The extractable concentrations of ABA associated with this closure were similar to those found in flooded plants. When an ABA-deficient ‘wilty’ mutant of pea was waterlogged, the extent of stomatal closure was less pronounced than that in ordinary non-mutant plants, and the associated increase in foliar ABA was correspondingly smaller. Similarly, waterlogging closed stomata of tomato plants within 24 h, but no such closure was seen in ‘flacca’, a corresponding ABA-deficient mutant. The results provide an example of stomatal closure brought about by stress in the root environment in the absence of water deficiency. The correlative factor operating between the roots and shoots appeared to be an inhibition of ABA transport out of the shoots of flooded plants, causing the hormone to accumulate in the leaves.     

Stomatal crypts may facilitate diffusion of CO2 to adaxial mesophyll cells in thick sclerophylls

In some plants, stomata are exclusively located in epidermal depressions called crypts. It has been argued that crypts function to reduce transpiration; however, the occurrence of crypts in species from both arid and wet environments suggests that crypts may play another role. The genus Banksia was chosen to examine quantitative relationships between crypt morphology and leaf structural and physiological traits to gain insight into the functional significance of crypts. Crypt resistance to water vapour and CO₂ diffusion was calculated by treating crypts as an additional boundary layer partially covering one leaf surface. Gas exchange measurements of polypropylene meshes confirmed the validity of this approach. Stomatal resistance was calculated as leaf resistance minus calculated crypt resistance. Stomata contributed significantly more than crypts to leaf resistance. Crypt depth increased and accounted for an increasing proportion of leaf resistance in species with greater leaf thickness and leaf dry mass per area. All Banksia species examined with leaves thicker than 0.6 mm had their stomata in deep crypts. We propose that crypts function to facilitate CO₂ diffusion from the abaxial surface to adaxial palisade cells in thick leaves. This and other possible functions of stomatal crypts, including a role in water use, are discussed.     

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.

     

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.     

Photosynthetic and structural acclimation to light direction in vertical leaves of Silphium terebinthinaceum

The azimuth of vertical leaves of Silphium terebinthinaceum profoundly influenced total daily irradiance as well as the proportion of direct versus diffuse light incident on the adaxial and abaxial leaf surface. These differences caused structural and physiological adjustments in leaves that affected photosynthetic performance. Leaves with the adaxial surface facing East received equal daily integrated irradiance on each surface, and these leaves had similar photosynthetic rates when irradiated on either the adaxial or abaxial surface. The adaxial surface of East-facing leaves was also the only surface to receive more direct than diffuse irradiance and this was the only leaf side which had a clearly defined columnar palisade layer. A potential cost of constructing East-facing leaves with symmetrical photosynthetic capcity was a 25% higher specific leaf mass and increased leaf thickness in comparison to asymmetrical South-facing leaves. The adaxial surface of South-facing leaves received approximately three times more daily integrated irradiance than the abaxial surface. When measured at saturating CO₂ and irradiance, these leaves had 42% higher photosynthetic rates when irradiated on the adaxial surface than when irradiated on the abaxial surface. However, there was no difference in photosynthesis for these leaves when irradiated on either surface when measurements were made at ambient CO₂. Stomatal distribution (mean adaxial/abaxial stomatal density = 0.61) was unaffected by leaf orientation. Thus, the potential for high photosynthetic rates of adaxial palisade cells in South-facing leaves at ambient CO₂ concentrations may have been constrained by stomatal limitations to gas exchange. The distribution of soluble protein and chlorophyll within leaves suggests that palisade and spongy mesophyll cells acclimated to their local light environment. The protein/chlorophyll ratio was high in the palisade layers and decreased in the spongy mesophyll cells, presumably corresponding to the attentuation of light as it penetrates leaves. Unlike some species, the chlorophyll a/b ratio and the degree of thylakoid stacking was uniform throughout the thickness of the leaf. It appears that sun-shade acclimation among cell layers of Silphium terebinthinaceum leaves is accomplished without adjustment to the chlorophyll a/b ratio or to thylakoid membrane structure.