The Humidity Response of Stomata and its Measurement

Meidner, H. 1987. The humidity response of stomata and its measurement.—J.exp. Bot. 38:877–882. Using artificial membranes of constant conductance with vapourpressures below the membranes of 2?33 kPa (saturated) and 2?26kPa (97% saturated) it was found that an automated water vapourdiffusion porometer registered a change in conductance. In otherwords, it underestimated the conductance when the vapour pressurebelow the membranes was only 97% saturated. This is becausethe programmed computation of the conductance assumes that thespace below the membrane is at all times saturated. The implicationsfor measuring leaf conductance with these instruments is discussedin connection with the humidity response of stomata to a stepwiseincrease in the vapour pressure difference between the leafinterior and the atmosphere. This response appears to involvea lowering of the vapour pressure in the sub-stomatal spaceand, therefore, a transient opening movement which can be detectedby sensitive mass flow porometry. It is concluded that in cases in which a transient opening movementprecedes partial stomatal closure the humidity response to anincrease in vapour pressure difference cannot be due to vapourloss direct from the guard cells. Key words: Humidity, transients, stomata     

Vapour Pressure Deficit Response of Cuticular Conductance in Intact Leaves of Fagus sylvatica L.

The cuticular conductance (g_c) of the astomatous adaxial surfaceof Fagus sylvatica L. leaves was determined under varying vapourpressure deficits at a constant temperature of 20 °C. Cuticularconductance was determined from the weight loss of detachedleaves after both the stomatous abaxial surface and the cutend of the petiole had been sealed using low melting-point paraffinwax. Cuticular conductance was found to decrease as the watervapour pressure was increased in steps. No response was observedwhen vapour pressure deficit was decreased from an initiallyhigh value. It is concluded that these results are consistentwith the hypothesis that cuticular conductance is influencedby the water content of the cuticle and that the apparent hysteresisis likely to be a result of the long time-constant for the processof cuticle rehydration in intact leaves. Key words: Cuticle, cuticular conductance, Fagus sylvatica L., Fagaceae, vapour pressure deficit, VPD     

Humidity Responses of Stomata and the Potassium Content of Guard Cells

Humidity responses of stomata and changes in the potassium contentof their guard cells were investigated in intact plants anddetached epidermal strips of Valerianella locusta (L.) Betcke.Potassium content was determined by Macallum‘s stain.It was found that changes in stomatal aperture caused by decreasingor increasing humidity were followed only after a delay by changesin the potassium content of the guard cells. By comparison,if stomatal movements occurred in response to changes in illuminationthe relative potassium content of the guard cells correlatedcontinuously with the changes in stomatal aperture. Since thepotassium content of the guard cells changed only after mostof the stomatal movements in response to changes in humiditywere completed changes in potassium content and humidity responsesof stomata can be described as following a hysteresis curve.     

The Response of Stomata of Pearl Millet (Pennisetum typhoides S. and H.) to Atmospheric Humidity

Canopy conductance of irrigated and unirrigated pearl milletplants was measured with a diffusive resistance porometer ina field experiment in Central India. When plants were growingin a drying soil, canopy conductance was related linearly tothe amount of light intercepted by the canopy, and was unaffectedby large changes in atmospheric saturation deficit When waterwas given to other plants growing in the same field, canopyconductance became strongly influenced by changes in saturationdeficit.     

Response of Stomata to Subnormal Carbon Dioxide Concentrations

In a preliminary note in Nature (vol. 161, p. 179, 1948) andin two recent papers in this Journal (vol. 1, pp. 29 and 227,1950) I described work leading to the finding that stomata ofPelargonium and of wheat respond markedly to small changes inthe carbon dioxide content of the air below the normal 0?03per cent.; I have now for the first time seen a paper by Freudenberger(Protoplastna, 25, 15, 1940) in which a similar discovery (inqualitative terms) is announced for Canna and some other genera.I much regret that owing to the war the volume of Protoplasmain question has not been available and I was thus unable torefer to this interesting paper. This work of Freudenberger'swill be discussed in relation to my own in due course.     

植物表皮蜡质参与干旱胁迫的反应机制

植物表皮是植物与外部环境直接接触的部位,包括具有立体网状结构的角质和填充其间并覆盖其上的蜡质。植物在适应外界环境的过程中,表皮蜡质形成了特殊的结构和复杂的化学组成。植物表皮蜡质最重要的功能是参与阻止植物非气孔性失水,提高植物对水分的利用效率,以实现对干旱环境的适应。干旱环境会导致植物表皮蜡质代谢的变化,这种变化最终通过调控基因表达来实现。目前已经发现了多个蜡质代谢相关基因参与了植物对干旱环境的适应,部分基因已经成功克隆并且用于改良农作物的抗旱性。但这些基因参与干旱响应的分子机制及其与ABA的关系并不很清楚。就植物适应水分胁迫而发生的包括蜡质组成和含量在内的代谢变化,以及该过程中所涉及的主要基因及其分子生物学研究进行综述。探讨表皮蜡质在植物适应干旱中的重要作用及其分子机制,可为农作物的抗旱育种提供新型的分子标记和重要靶基因,最终服务于农业生产实践。     

Comparative Responses of Leaf Conductance to Humidity in Single Attached Leaves

Water vapour conductances of single attached leaves were measuredover a range of humidities in 12 annual species grown underone set of environmental conditions in a controlled environmentchamber, as well as in several of these species grown at differentair temperatures and levels of irradiance. Low growth temperaturedecreased the sensitivity of leaf conductance to changes invapour pressure difference, whereas low levels of irradianceduring growth increased the sensitivity. The degree of changein sensitivity with change in growth environment varied betweenspecies. There was a wide range of sensitivities of leaf conductancein species grown in the same environment, without any relationshipto pathway of photosynthetic carbon fixation or climatic range.A strong relationship between sensitivity of leaf conductanceand the length of the root system per unit of plant area wasfound between species and between growth environments. Thisrelationship could be used to predict accurately the sensitivitiesof leaf conductance for plants grown in other environments.     

Stomatal Response to Humidity and Lanthanum

Lanthanum fed to the base of excised leaves of Sesamum indicum L. and Helianthus annuus L. was used as a tracer to investigate by electron microscopy the path of water in the apoplast of leaves. The generally random distribution of lanthanum in cell walls provided no support for the hypothesis that cuticular transpiration may be greater for guard cells than for adjacent epidermal cells. Occasionally, accumulations of lanthanum were observed in anticlinal walls of epidermal cells and at the outer surface of the plasma membrane but lanthanum was not observed in the symplast. The influx of ⁸⁶Rb to excised roots of sesame and sunflower was inhibited during incubation with 0.5 mM lanthanum or calcium for 15 or for 180 min. Stomata of sunflower partially closed when 2.5 mM lanthanum was supplied to the base of excised shoots in a potometer, whereas this treatment had little effect on stomatal conductance of sesame shoots maintained in a constant environment. Supplying 2.5 mM lanthanum to the base of sesame shoots strongly inhibited stomatal opening response to increase in ambient humidity but had little effect on stomatal opening response to light. It was concluded that stomatal opening response to increased humidity may be dependent upon some process, such as ion influx, that is inhibited by lanthanum, and that opening response to humidity may differ in mechanism from stomatal opening response to increased irradiance.     

植物气孔对全球环境变化的响应及其调控防御机制

气孔是植物与环境发生联系的重要门户,控制着植物与外界的气体和水分交换。本文针对全球大气CO2浓度升高、气候变暖、干旱加剧等环境问题,分析了气孔对全球水循环、碳循环的重要贡献。系统总结了气孔的形态发育和生理功能对大气高CO2浓度、干旱、土壤盐渍化、病虫害等的响应及其调控防御机制。综述了脱落酸（ABA）、Ca2＋、H2O2、一氧化氮（NO）和光信号调控气孔运动的分子机制。从理论和实践两方面,提出了通过调控气孔运动协调CO2同化和水分散失的矛盾,在不影响光合效率的前提下提高水分利用率等未来的研究方向。     

Rapid, Blue-Light-Induced Transpiration Response Restricted to Plants with Grass-like Stomata

It is shown that the response of transpiration to light is different in species from Gramineae and Cyperaceae compared to species from other families. Blue light (380–500 nm) causes both a rapid response (rise time 2 min) and a slow response (rise time 5 to 10 min) in species from these two families but induces only a slow response in other families. Red light results only in a slow response in all plants investigated. It is hypothesized that the rapid response to blue light is due to the special anatomy and/or function of the so-called grass-like (graminaceous) stomata of plants belonging to Gramineae or Cyperaceae.     

Stomata and plasmodesmata

Summary In developing epidermal tissue ofPhaseolus vulgare L. complete plasmodesmatal connections occurred between guard cells and epidermal cells and between sister guard cells of a stoma but they were not seen in fully differentiated tissue. However, incomplete, aborted plasmodesmata were occasionally seen in the common guard/epidermal cell wall, usually connected to the epidermal cell protoplast, in mature tissue. Plasmodesmatal connections between neighbouring epidermal cells were commonly observed in tissue at all stages of development. In all locations, the plasmodesmata were usually unbranched occurring singly or in small pit fields; very rarely branched, incomplete plasmodesmata were also seen in the wall between mature guard and epidermal cells. The significance of these findings were related to stomatal functioning and to the development of plasmodesmata in general.     

Delay in the Response of Stomata to Abscisic Acid in CO2-free Air

Abscisic acid (10^–5 M) was fed via their petioles to leavesdetached from well watered plants of Xanthium strumartum, whilethe intercellular spaces were flushed with air of known CO₂content. A closing response to ABA occurred in the presenceor absence of CO₂, and the stomata responded to CO₂ whetheror not ABA was supplied to the leaves. A factorial experimentrevealed no interaction between CO₂ and ABA, and suggested thattheir effect on the rate of closure was purely additive. Theonly evidence of interdependence between the two corn poundswas a delay in the response to ABA in C0 air, which was moremarked in a high light intensity. A hypothesis which is consistentwith the data is that ABA induces stomatal closure by interferingwith the energy supply required for the active transport processeson which guard cell turgor depends. The inhibitory action ofABA takes longer in CO₂-free air because, in the absence ofCO₂ fixation, energy is available from chioroplasts as wellas mitochondria.     

Humidity Pretreatment Affects the Responses of Stomata and CO2 Assimilation to Vapor Pressure Difference in C3 and C4 Plants

Experiments were carried out to investigate the long-term influenceof humidity on the short-term responses of stomata and CO₂ assimilationto vapor pressure difference in Oryza sativa (rice, C₃ species)and Panicum maximum (green panic, C₄ species). Plants were grownfor four weeks in growth chambers set at 35% and 85% relativehumidity at 25C air temperature, 38+2 Pa CO₂ partial pressureand 1,700µmol m^-2s^-1 photon flux density. Soil was saturatedwith water in both humidity treatments. Low humidity pretreatmentscaused low leaf conductance and low rates of transpiration andCO₂ assimilation in O. sativa, but small changes in stomatalresponses to humidity and in CO₂ assimilation were found inP. maximum. From the short-term gas exchange experiments, itwas noted that the responsiveness of leaf conductance to vaporpressure difference were affected by humidity pretreatmentsin O. sativa, whereas unaffected in P. maximum. In O. sativameasurements of CO₂ assimilation as a function of internal CO₂partial pressure (A-Ci curve) indicated that low humidity pretreatmentsreduced the CO₂ assimilation at high internal CO₂ partial pressure,but the initial slope of the A-Ci curve was unaffected. Furthermore,plant characteristics such as total dry weight and leaf areaof plants subjected to low umidity were lower than plants subjectedto high humidity. The reductions in O. sativa, however, werelarger than in P. maximum. Stomatal frequency from low humiditygrown plant was higher than that from high humidity grown plantsin both species although there is no significant difference.The data indicated that if the short term inhibition of netCO₂ assimilation at a high vapor pressure difference was imposedduring vegetative growth, the photosynthetic biochemistry andthe resultant plant growth were largely depressed in O. sativa,a C₃ species. (Received May 26, 1992; Accepted November 2, 1992)     

Stomatal Response of Citrus jambhiri to Water Stress and Humidity

Seven-month-old rough lemon (Citrus jambhiri Lush.) seedlings were subjected to high- and low-humidity treatments (vapor pressure deficits of 8.0 and 19.6 mbar) for 3 weeks. Half of each group was well supplied with water and half was subjected to a series of three drying cycles in which xylem pressure potential fell to below ?25 bar. The relationship between leaf conductance and xylem pressure potential was similar during each drying phase and was unaffected by atmospheric humidity. Several days elapsed after rewatering before normal stomatal opening occurred. When all the plants were subsequently kept well watered, leaf conductances decreased as the leaf-to-air vapor pressure difference was increased. However, the conductances of previously stressed plants were lower than those of unstressed plants, and consequently previously stressed plants had lower transpiration rates.     

Assessment of the Response to Selection for Leaf Water Conductance in Lolium perenne

Measurements of leaf water conductance (LWC) were made in agrowth room on plants previously selected for either high orlow LWC as seedlings from two Lolium perenne L. populations.Differences in LWC were maintained between selection groupswhen measured as older plants, but there were considerable changesin LWC of individual selection groups on remeasurement. TheLWCs and the rankings of LWCs of individual genotypes were correlatedbetween experiments, thus demonstrating that selection of genotypeswas worthwhile. Thus the possibility of including LWC in selectionprogrammes was established. Investigations conducted to optimize sampling for LWC are described.It was concluded that little further reduction in the standarderror of LWC measurements was obtained by making more than eightmeasurements per genotype, and it was important to sample onat least four tillers. A new measure for the phenotypic stabilityof a selection group is proposed, named realized ‘selectivity’.The realized selectivity can be used to estimate the upper valuefor realized heritability and is about 0.5 for LWC in L. perenne.The values of phenotypic repeatability of LWC are compared withother similar measurements. Lolium perenne L, leaf water conductance, selection, components of variance, scale of measurement     

Prechilling of Xanthium strumarium L. Reduces Net Photosynthesis and, Independently, Stomatal Conductance, While Sensitizing the Stomata to CO(2)

Greenhouse-grown plants of Xanthium strumarium L. were exposed in a growth cabinet to 10 C during days and 5 C during nights for periods of up to 120 hours. Subsequently, CO₂ exchange, transpiration, and leaf temperature were measured on attached leaves and in leaf sections at 25 or 30 C, 19 C dew point of the air, 61 milliwatts per square centimeter irradiance, and CO₂ concentrations between 0 and 1000 microliters per liter ambient air. Net photosynthesis and stomatal conductance decreased and dark respiration increased with increasing duration of prechilling. The reduction in net photosynthesis was not a consequence of decreased stomatal conductance because the intercellular CO₂ concentration in prechilled leaves was equal to or greater than that in greenhouse-grown controls. The intercellular CO₂ concentration at which one-half maximum net photosynthesis occurred remained the same in prechilled leaves and controls (175 to 190 microliters per liter). Stomata of the control plants responded to changes in the CO₂ concentration of the air only slightly. Prechilling for 24 hours or more sensitized stomata to CO₂; they responded to changes in CO₂ concentration in the range from 100 to 1000 microliters per liter.     

The Stomata of Gnetum

In both Gnetum gnemon and G. ula the atomatal development inthe collars and axes of the male and female cones and the outertwo envelopes of the ovule is of the haplocheilic type. In theleaf some stomata do show parallel subsidiary cells, but theyarise from the surrounding epidermal cells and do not seem tohave a common origin with the guard cells. This conflicts withearlier accounts and is of interest in relation to the typesof stomata met with in other gymnosperms, living and fossil.     

Stomata and transpiration of droopy potatoes

A diploid potato (Solanum tuberosum) mutant called droopy wilts easily. Excised leaves of the mutant lost weight, and hence water, more rapidly and had many more open stomata than leaves of a normal sibling. Further, the stomata of abnormal plants remained open in wilted leaves. When the stomata of the abnormal mutant were closed by a chemical spray, its excised leaves lost water no more rapidly than normal. Thus, the wilting of the mutant must be caused by wide stomata. The wilting of the abnormal leaves and the small dry weight of the plants indicate the advantage of the stomatal hydrostat in the normal plants.     

短期整体身心调节法的全身皮肤电导反应规律(英文)

目的:探讨短期整体身心调节法练习者的全身皮肤电导反应特点。方法:采用单因素完全随机实验设计,将68名在校大学生分为整体身心调节组和放松组,分别进行为期10天的整体身心调节训练和经典的肌肉放松训练,并于训练前和训练结束后,测试两组学生身体7个分支的皮肤电导反应。结果:训练前,大学生前3支皮肤电导反应大于后4支;训练10天后,与训练前相比,整体身心调节训练组第1、2支皮肤电导反应显著减小,7个分支的皮肤电导反应出现均衡的规律;放松训练组学生身体7个分支皮肤电导反应变化不显著。结论:短期整体身心调节法形成了全身皮肤电导反应的均衡,可能反映短期整体身心调节法的整体身心相互作用原理。