Studies in Stomatal Behaviour: II THE ROLE OF STARCH IN THE LIGHT RESPONSE OF STOMATA PART 4. VARIATION UNDER CONSTANT CONDITIONS

A quantitative study has been made of the extent and natureof the variation in starch-content and aperture of the stomataof Pelargonium. It is shown that distribution over the surfaceof a single leaf is substantially normal in form; that underexperimental conditions in common use there is a highly significantdifference between groups of stomata on the lower epidermisof a single leaf; that the variation between different leaveson the same plant, or between similar leaves on different plants,does not differ significantly from that between strips fromthe same leaf; that not less than 20 stomata should be measuredon each strip; and that pore-width is a satisfactory measureof the area of the stomatal aperture.     

The effect of cyclic salt in a maritime environment

Summary A previous paper (Part I)⁴ has shown that when vegetation and land slope are favourable to the capture of aerosol, the salinity of rainfall provides no measure of rate of acquisition of cyclic salt by a given land area.This is confirmed by the high level of chloride in Fiji foliage.The chloride content of experimental rice plants was found to be much higher than could be accounted for by all the chlorides introduced into the growth medium.Rice plants in the field, affected by the punctures of leaf hoppers, were shown to have a higher level of leaf chloride than unaffected plants.Chloride absorbed through the leaves was distributed in the plant differently from chloride taken up by the roots.Measurements on stomata and specific leaf area suggest that the aerosol particles enter through the stomata rather than through the rest of the leaf surface.     

Studies on the structural and developmental variation and distribution of stomata in the Rubiaceae

The structure and ontogeny of the stomata has been studied in 26 species of Rubiaceae, in relation to their organographic distribution. The stomata are mostly paracytic on the leaves, but vary on other parts, particularly on the floral disk, where they are exclusively anomocytic. The foliar stomata are mesogenous and paracytic, but may be either dolabrate or trilabrate in origin. The disk stomata are perigenous and are probably derived from the mesogenous paracytic ones by the loss of divisive potential of their meristemoid due to anthogenetic factors. They are regarded to be hydathodal in function. If the dendroid habit is regarded as primitive, in the family, trilabrate stomata were quite possibly derived from dolabrate ones, which are mostly associated with the dendroid habit. Evidence from stomatal ontogeny is shown to be taxonomically important in the Rubiaceae.     

Osservazioni Sulla Maggiorana (Origanum Majorana L.) in Veste di Pianta Coltivata

Abstract

Stomatal features and ontogeny of stomata of 11 ornamental taxa of monocotyledonous families with Agavaceae (1 species), Amaryllidaceae (1 species), Araceae (3 species), Cannaceae (1 species), Commelinaceae (3 species), Liliaceae (1 species), and Musaceae (1 species) have been studied. Features like stomatal area, leaf area occupied by stomata and per cent leaf area occupied by stomata are reported for these taxa for the first time.     

Cadmium effects on leaf transpiration of sugar beet (Beta vulgaris)

Seedlings of sugar beet ( Beta vulgaris L. cv Monohill) were cultivated for 4 weeks in nutrient solution containing different concentrations of CdCl₂ (0 to 10 μ M ). The effects of Cd on appearance and function of stomata and leaf cuticle were investigated by water loss measurements and microscopy. The leaf transpiration rate increased with increasing Cd concentrations while the sum total of stomatal aperture area per unit leaf area decreased. Already at low Cd levels. an increase of defective and undeveloped stomata was found in Cd treated plants. These stomata are closed or have small apertures and probably lack a functional closing mechanism. The number of intact stomata per unit leaf area was lower in leaves of Cd treated plants than in controls, and Cd induced closure of intact stomata. The total number of stomata per leaf area slightly increases with increasing Cd concentration. as does the percentage of small stomata. Furthermore. specific leaf area increased, while the density of leaf structure was decreased by Cd. From this observation we conclude that the increase in transpiration rate caused by Cd is primarily due to effects on the permeability of the leaf cuticle to water.     

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     

田野菟丝子寄生对薇甘菊气孔行为的影响

田野菟丝子寄生已成为当前控制薇甘菊入侵蔓延的最佳生物防治手段之一。应用扫描电子显微镜技术,观察并统计分析了田野菟丝子寄生对薇甘菊叶片气孔形态参数的影响,为了解寄生对薇甘菊生理特征的影响提供一定的形态学依据。结果表明,田野菟丝子寄生对薇甘菊叶片的气孔长宽比和气孔面积产生显著影响:对照薇甘菊叶片的气孔长宽比和气孔面积表现为双峰日变化动态;而被寄生的薇甘菊的叶片气孔长宽比和气孔面积则表现为单峰日变化规律。对照薇甘菊气孔的长宽比分别在12:00和10:00,气孔面积分别在10:00和14:00达到日变化中的最大值与最小值;在15:00到16:00气孔长宽比和气孔面积再一次达到一个峰值,使气孔长宽比和气孔面积的日波动形成一个双峰曲线。被寄生的薇甘菊的叶片气孔长宽比和气孔面积则表现出单峰曲线,峰值分别出现在12:00和14:00。田野菟丝子寄生对薇甘菊的气孔密度没有产生显著影响。     

Automatic measurement of stomatal density from microphotographs

Key message

An automated process using a cascade classifier allowed the rapid assessment of the density and distribution of stomata on microphotographs from leaves of two oak species.

Abstract

Stomatal density is the number of stomata per unit area, an intensively studied trait, involved in the control of CO₂ and H₂O exchange between leaf and atmosphere. This trait is usually estimated by counting manually each stoma on a given surface (e.g., a microphotograph), usually repeating the procedure with images from different parts of the leaf. To improve this procedure, we tested the performance of a cascade classifier to automatically detect stomata on microphotographs from two oak species: Quercus afares Pomel and Quercus suber L. The two species are phylogenetically close with similar stomatal morphology, which allowed testing the reuse of the cascade classifier on stomata with similar shape. The results showed that a cascade classifier trained on only 100 sample views of stomata from Q. afares was able to rapidly detect stomata in Q. afares as well as in Q. suber with a very low number of false positives (5 %/1.9 %) and a small number of undetected stomata (14.8 %/0.74 %), when partial stomata near the edge of the microphotographs were ignored. The remaining undetected stomata were due to obstacles such as trichomes. As an example of further applications, we used the positions detected by the cascade classifier to assess the spatial distribution of stomata and group them on the leaf surface. To our knowledge this is the first time that a cascade classifier has been applied to plant microphotographs, and we were able to show that it can dramatically decrease the time needed to estimate stomatal density and spatial distribution.     

Stomatal control of transpiration

The role of stomata in regulating transpiration from vegetation has historically been controversial among those working either at the single leaf, or at the extensive canopy scales. Recently, the role of unstirred air layers surrounding leaves and canopies in limiting the impact of stomatal movements on transpiration has received renewed recognition. This has led to notable progress in quantitatively describing the effectiveness of stomata in controlling transpiration and in reconciling contrasting viewpoints concerning the role of stomata at the leaf, stand and regional scales. Considerable progress has also been made in understanding how variations in aerial factors such as evaporative demand and edaphic factors such as soil water availability are sensed and transduced into appropriate stomatal regulatory responses. These developments indicate that studies carried out at multiple scales of observation are needed to understand how external environmental factors and intrinsic plant properties interact to determine the role of stomata in regulating transpiration from different types of vegetation.     

The stomata of the cork-oak, Quercus suber. An ultrastructural approach

In the evergreen leaves of Quercus suber, stomata play a major role in adaptation to drought and temperature stress. The leaf is of zygostomic type and has about 430 stomata per square milimeter of abaxial leaf surface. The stomatal complex is of the anomocytic type. The guard cells protrude from the epidermal plane. The guard cell nucleus contains heterochromatin in small granules. The guard cell cytoplasm is characterised by a large number of well developed mitochondria, amyloplasts with stroma and grana, and a well developed cytoskeleton with a cortical array of microtubules oriented pa railed to the slit axis that persist even in mature cells. Guard cell walls are asymmetrically thickened and devoid of plasmodesmata. No area of cell walls was free of cuticle or covered by a thin cuticular layer and apparently no area of limited cuticular development provides evaporation when the stomata are closed.     

A New Porometer Based upon the Electrical Current Produced by Guard Cells

Stomatal guard cells extrude protons when the stomata open.This gives rise to an electrical current which is proportionalto the degree of stomatal opening. An instrument has been developedto measure this leaf surface current which is, in effect, anew type of porometer. The performance of the new porometerhas been compared with that of a commercially available diffusionporometer and a close relationship between leaf surface currentand stomatal conductance was observed for all the species investigated.It is concluded that the instrument has several advantages overthe diffusion porometer, in particular, its small size and simplicityof operation, making it especially suitable for use in the field. Key words: Leaves, stomata, electrical currents, porometry     

Stomatal Morphology during Acclimatization of Tobacco Plantlets to ex vitro Conditions

Image analysis was used in studying stomatal morphology during acclimatization of tobacco plantlets to ex vitro conditions, 45 d after transfer leaf area was 15 times, and total number of stomata per leaf four times increased. During acclimatization stomatal density was decreased considerably on both leaf sides, and was compensated by an increase in stomatal sizes, e.g., in stomatal length and in stomatal area (both guard cells and pore). Elongation of stomata was increased indicating that the originally circular stomata of in vitro plantlets were changed into elliptical ones in ex vitro acclimatized plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

中国葡萄属植物叶片气孔特征的研究

对起源于中国的葡萄属(Vitis L.)20个种或变种叶片气孔特性进行了观察研究。结果表明:气孔纵径对葡萄属种的分类有较大的价值;气孔比密度(叶片上所有气孔复合体面积与叶片面积之比)与叶片大小呈极显著正相关;气孔密度与气孔纵径呈极显著负相关;所有观察种类的叶片气孔类型均为不规则型。     

Localization of mechanisms involved in hydropassive and hydroactive stomatal responses of Sambucus nigra to dry air

The response of stomata to a reduction of air humidity is composed of a hydropassive opening followed by active closure. Whereas the mechanisms behind the hydropassive opening are largely understood, the location and physiological basis of the sensing mechanisms leading to active closure are not yet known. This study attempts to evaluate the importance of a single pore's transpiration on its own response and that of adjacent pores. Selected stomata on attached intact leaves of Sambucus nigra were sealed with mineral oil and the response to a reduction of humidity was continuously observed in situ. Blocking a pore's transpiration had no appreciable effect on hydropassive opening and subsequent stomatal closure. If the adjacent stomata were additionally sealed, the closing response was reduced, but not the hydropassive opening. On the other hand, sealing the entire leaf surface, except a small area including the observed stomata, also reduced stomatal closure. These results indicate that strictly local processes triggered by a pore's own transpiration are not required to induce stomatal closure. To describe the effect of one pore's transpiration on the hydropassive and hydroactive responses of neighboring stomata, a simple spatial model was constructed. It suggests that 90% of the closing effect covers an area of approximately 0.5 mm2, whereas the effect on hydropassive opening affects an area of approximately 1 mm2. This divergence may suggest mechanisms other than or in addition to those involving changes of local leaf water potential.     

Effects of infection by Phytophthora injestans (Mont.) de Bary on the stomata of potato leaves

Phytophthora injestans infection of potato leaves causes abnormal opening of the stomata in the tissue colonized by the fungus before sporangiophores emerge through them. The affected area, which may be up to 7 mm wide, extends from the necrotic tissue to within 1–2 mm of the advancing edge of the colonizing mycelium. These stomata open wider than those in uninfected parts of the leaf, and do not close in the dark, but closure can be induced experimentally by a high water deficit. Affected guard cells have an increased osmotic value, reduced starch content, and show degradation of the chloro-plasts. No direct infection of the guard cells has been observed. Autoradiography of infected leaflets which had been exposed to ¹⁴CO₂ in the light, showed that a zone of increased photosynthesis occurs in the region of wide-open stomata.     

Variable Cell Lineages form the Functional Pea Epidermis

Evidence was sought for cellular programs and cellular interactionsacting during the formation of stomatal spacing patterns. Dailyreplicas of the surfaces of Pisum sativum leaves were used toreconstruct the cellular development of specific regions ofthe epidermis. During the period studied small primordia becamemature leaves; this involved a 250-fold increase in area anda 20-fold increase in cell number. The earliest event correlatedwith the development of a stoma was an unequal division, andsuch divisions were common in neighbouring and even within thesame cells. A distinct cell lineage started with these unequaldivisions, forming both a stoma and most of the cells that separatedit from its neighbours. Both products of an unequal divisionbecame regular epidermal cells only where such development preventedthe formation of two stomata that would have been in directcontact with one another. Neighbouring stomata often developedand matured together, indicating that there was no mutual inhibitionbetween developing stomata that were more than one cell apart.It is concluded that stomata are products of an intracellularprogram which generates stomatal patterns during rather thanpreceding development. This program can be modified and evenstopped during its entire course, allowing for the correctionof local ‘mistakes’ of stomatal patterning. Cell lineages, cell determination, cellular interactions, epidermal development, garden peas, immature stomata, pattern formation, Pisum sativum, spacing patterns, stomata, unequal divisions     

蛇足石杉的形态学及不同光照处理下气孔特征的研究

对蛇足石杉的形态学特征进行了重新描述,并对不同光照处理下蛇足石杉叶片的气孔特征进行比较。结果表明：在一定范围内,随着环境中光照强度的增加,气孔长度和宽度、单个气孔面积、气孔密度及气孔总面积都呈增加的趋势。当光照强度超过某一阈值时其气孔指数和气孔密度仍呈增加的趋势,但气孔长度、宽度和单个气孔面积呈变小趋势。小而密的气孔是其适应旱生环境的表现,表明其具有一定的生态适应能力,但进行人工栽培时应避免光照过强。     

Gas exchange of a desert shrub (Zygophyllum dumosum Boiss.) under different soil moisture regimes during summer drought

The effects of soil water potential on photosynthesis and transpiration of whole Zygophyllum dumosum Boiss. shrubs were examined with a field IRGA system during a rainless summer. Daily photosynthesis and transpiration activities were not notably different on a unit phyllode area basis among shrubs at naturally differing soil water potentials. Irrigation of shrubs caused phyllodes to increase significantly in water content and new leaflets to appear. Leaflets had three times as many stomata per unit area (23000 stomata cm^-2) as phyllodes (7100 stomata cm^-2) but photosynthesis and transpiration rates were not measurably different between irrigated and non-irrigated shrubs on a unit area basis. This finding suggests that sufficient soil moisture will lead to increased carbon uptake of the entire shrub simply because the total area of photosynthesizing tissue increases. Gas exchange rates appear to be controlled solely by atmospheric conditions under the stresses of summer.     

外源脯氨酸对自然干旱下白刺叶片气孔的影响

以大田环境内多年生荒漠植物白刺（Nitraria tangutorum）为研究对象,采用扫描电子显微镜对不同外源脯氨酸质量浓度处理下白刺叶片气孔进行微观结构观察并测定叶片表皮气孔器长度、宽度、面积和密度,比较同一指标在不同脯氨酸质量浓度处理下的差异。采用室外试验研究自然干旱胁迫下喷施质量浓度为50、100、150、200、250 mg·L^-1的外源脯氨酸（Proline,缩写为Pro或P）研究白刺的耐旱性。观察结果显示,白刺叶片气孔保卫细胞为肾形,气孔在叶片表皮随机分布,气孔器多为无规则型,气孔呈椭圆形且叶片表面蜡质较少,并且叶片细胞出现褶皱和下陷。与对照相比,在不同质量浓度处理和不同采样时间时,气孔长度、宽度及面积下降,气孔密度增大,随着浓度的升高以及采样时间的变化,气孔长度整体呈现下降趋势,当浓度达到200 mg·L^-1时,下降幅度增大,宽度和面积整体呈现先降低后升高再降低的趋势,而气孔密度则整体呈现上升趋势,其中,气孔长度、宽度和面积在质量浓度为50 mg·L^-1、采样第1天时达到最大值,气孔密度在质量浓度为150 mg·L^-1、采样第9天时达到最大值。此外,气孔长度在不同浓度脯氨酸处理下第1、6和9天存在显著差异,而气孔宽度和面积差异不显著,除第0天外,气孔密度因脯氨酸质量浓度不同均差异显著（P<0.05）。研究结果表明,自然干旱胁迫下对白刺叶片喷施不同质量浓度的外源脯氨酸,可减小气孔长度、宽度和面积,而增加气孔密度,以期为白刺抗旱提供理论依据。     

黄土高原丘陵沟壑区抗侵蚀植物叶表皮的生态适应性

采用叶表皮临时装片法研究了黄土高原丘陵沟壑区不同土壤侵蚀环境沟间地、沟谷地和沟间人工刺槐林地6种抗侵蚀植物叶表皮组成细胞的形态特征.结果表明: 沟间地抗侵蚀植物叶的上表皮气孔开度、气孔密度、气孔指数、气孔器长宽比可塑性、气孔器面积可塑性、表皮毛〖JP2〗密度和表皮细胞密度分别比沟谷地提高93.8%、66.8%、17.9%、36.4%、42.3%、199.4%和46.5%,下表皮分别提高90.4%、76.6%、9.8%、47.1%、43.9%、98.2%和50.1%;沟间人工刺槐林地叶上表皮各形态指标分别比沟谷地提高66.7%、20.5%、11.9%、37.9%、19.8%、113.1%和10.8%,叶下表皮分别提高106.7%、45.8%、11.9%、41.3%、21.2%、52.2%和28.1%.沟间地植物叶上、下叶表皮毛长度分别比沟谷地缩短58.8%和29.7%,表皮细胞面积分别比沟谷地减少40.3%和37.0%.沟间人工刺槐林地叶上、下表皮毛长度分别比沟谷地缩短25.0%和23.6%,表皮细胞面积分别比沟谷地减少22.2%和19.2%.抗侵蚀植物通过增加叶表皮气孔开度、气孔密度、气孔指数、气孔器长宽比可塑性、气孔器面积可塑性、表皮毛密度、表皮细胞密度和减少表皮毛长度、表皮细胞面积来适应较强的土壤侵蚀环境.