Statistical Distribution of Stomatal Apertures of Vicia faba and Hordeum vulgare and the Spannungsphase of Stomatal Opening

Plants of Vicia faba and Hordeum vulgare were grown in growthboxes with 7 mW cm^–2 PAR, 14 h day/10 h night, at 22/20°C. Stomata of attached leaves were measured under controlledconditions by means of an optical microscope and the distributionfunctions of the widths of pores were established. For Viciafaba they appeared to be symmetrical bell-shaped functions.In the process of stomatal opening or closure the shape of thedistribution remained constant, its maximum sliding left andright along the aperture axis. This result has been interpretedto mean that increments or decrements of apertures were equalfor all stomata independent of their individual apertures. Theconclusion has been drawn that the ‘driving force’is evenly distributed, equal for all stomata, and varies withinwider limits than is possible for stomatal apertures. Stomatalopening is limited by the closed state from below and by ananatomically possible maximum aperture from above.     

Stomatal Functioning of In Vitro and Greenhouse Apple Leaves in Darkness, Mannitol, ABA, and CO2

Leaves from in vitro and greenhouse cultured plants of Malusdomestica (Borkh.) cv. Mark were subjected to 4 h of darkness;4 h of 1 M mannitol induced water stress; 1 h of 10^–4M to 10^–7 M cis-trans abscisic acid (ABA) treatment; 1h of 0.12% atmospheric CO₂. Stomatal closure was determinedby microscopic examination of leaf imprints. In all treatments,less than 5% of the stomata from leaves of in vitro culturedplants were closed. The diameter of open stomata on leaves fromin vitro culture remained at 8 µm. In contrast, an averageof 96% of the stomata on leaves of greenhouse grown plants wereclosed after 4 h in darkness; 56% after 4 h of mannitol inducedwater stress; 90% after 1 h of 10^–4 M ABA treatment; 61%after 1 h in an atmosphere of 0.12% CO₂. Stomata of in vitroapple leaves did not seem to have a closure mechanism, but acquiredone during acclimatization to the greenhouse environment. Thelack of stomatal closure in in vitro plants was the main causeof rapid water loss during transfer to low relative humidity.     

After-effect of Water Stress on Stomatal Opening Potential: I. TECHNIQUES AND MAGNITUDES

The after-effect of a period of water stress upon the light-openingability of stomata was studied in tobacco (Nicotiana tabaccum)and broad bean (Vicia faba). Stomatal opening was always measuredafter floating leaf discs on water under favourable conditionsof light and temperature to obtain maximal opening at full leafturgor. Thus possible interference due to persistence of leaf-waterdeficits in the post-stress leaves was eliminated. Stomatalaperture was accurately estimated using a resistance porometer;values so obtained were substantiated by the direct measurementof aperture. Two to 4 days of wilting of tobacco, producing leaf-water deficitsof 30 to 40 per cent, had a marked after-effect on tobacco stomata.The ability to open in light was depressed and complete recoveryfrom this depression required 2 to 5 days after rewatering.In some cases over-recovery was observed; this was probablyrelated to a physiologically younger condition of leaves ofstressed plants following turgor recovery. In beans similarstresses caused after-effects smaller in magnitude but qualitativelysimilar to those in tobacco. In both tobacco and beans the magnitudeof the after-effect was approximately proportional to the leaf-waterdeficit attained immediately prior to rewatering.     

Characterization of a wilty sunflower (Helianthus annuus L.) mutant II. Water relations, stomatal conductance, abscisic acid content in leaves and xylem sap of plants subjected to water deficiency

The response of w-1, a wilty sunflower (Helianthus annuus L.)mutant, to water stress is described in comparison with thecontrol line (W-1). Detached leaves of w-1 strongly dehydratedduring the first 30 min without significant changes in leafconductance, whereas W-1 responded rapidly to water loss byreducing stomatal aperture. After 2 h stress ABA increased slightlyin w-1, while W-1 leaves showed a 20-fold increase. When waterstress was imposed to potted plants by water withholding, w-1quickly dehydrated, and lost turgor, while W-1 maintained positiveturgor values for a longer period. Wild-type plants respondedto small changes in leaf water potential by accumulating ABAand by closing stomata, whereas in the mutant significant changesin ABA content and in stomatal conductance were found only atvery low water potentials. In another experiment in which waterwas withheld under high relative humidity, when soil water contentstarted to decrease W-1 rapidly closed stomata in the absenceof any change in leaf water status and the reduction in conductancewas paralleled by a rise in xylem sap ABA concentration. Bycontrast the mutant started to accumulate ABA in the xylem sapand to close stomata when soil water content and leaf waterpotential were dramatically reduced. The low endogenous ABAlevels and the inability to synthesize the hormone rapidly eitherin the leaves or in the roots seem to be responsible for thehigh sensitivity of w-1 to water stress. Key words: ABA, Helianthus annuus L, water relations, stomatal conductance, drought, wilty mutant     

Stomatal responses to rapidly imposed water stress and light/dark transition in norflurazon-treated wheat leaves

Hoglund, H. O. and Klockare, R. 1987. Stomatal responses to rapidly imposed water stress and light/dark transition in norflurazon-treated wheat leaves.
Stomatal responses to rapidly imposed water stress and to light/dark transition were studied in leaves of wheat ( Triticum aestivum L. cv. Starke II) treated with nor-flurazon (NF) which is known to inhibit abscisic acid (ABA) accumulation. The stomatal response was studied in an open air flow system. It was shown that these plants have the ability to respond to externally added ABA. When the water potential in the nutrient solution was rapidly reduced, stomata in green plants responded with a transient opening followed by a strongly decreased aperture. NF-treated plants responded with a similar rapid opening of stomata, but the following closure was strongly reduced. Transfer from light to darkness induced a rapid closure of stomata in green plants but the closing response was strongly delayed in NF-treated plants. These results indicate that NF affects one or more regulators involved in the closure of stomata under rapidly imposed water stress and in the light/dark transition. The possibility that this regulator is ABA is discussed.     

Studies in Stomatal Behaviour: XI. FURTHER OBSERVATIONS ON RESPONSES TO NIGHT LENGTH

Stomatal opening in high-intensity light after long and shortnights was measured with the differential transpiration porometerand the Wheatstone bridge porometer on attached and detachedleaves of Xanthium pennsylvanicuin. Results from both porometersshowed that the rate of opening was markedly affected by night-lengthtreatment, but there was no effect on time of onset of openingor on the maximum aperture achieved. Attached and detached leavesshowed practically the same responses. In another experimentdifferent night-length treatments were simultaneously appliedto two leaves on the same plant. They apparently reacted independentlyto the treatments. Night-length effects on rate of opening arediscussed in relation to recent work by other authors on bananaand Vicia faba.     

水分胁迫下花生叶片AhNCED1蛋白表达与气孔开度的变化

研究了水分胁迫下不同花生抗旱品种叶片气孔开度和相对含水量变化,分析TAhNCEDI基因和AhNCED1蛋白进行表达情况,发现水分胁迫下,叶片相对含水量下降,叶片气孔开度降低,叶片AhNCED1基因和AhNCED1蛋白表达增强。抗旱品种较之敏旱品种在响应水分胁迫初期时（1h）AhNCED1基因和AhNCED1蛋白表达较强,叶片气孔开度下降较快,引发气孔关闭,其叶片相对含水量较高,保水能力较强。ABA合成抑制剂naproxen处理后,叶片AhNCED1基因和AhNCED1蛋白的表达减弱,气孔开度快速增加,水分胁迫下花生叶片AhNCED1蛋白表达可能影响气孔开闭。     

Senescence-Associated Changes during Long-day-induced Leaf Senescence and the Nature of the Graft-transmissible Senescence Substance in Kleinia articulata

Schwabe, W. W. and Kulkarni, V. J. 1987. Senescence-associatedchanges during long-day-induced leaf senescence and the natureof the graft-transmissible senescence substance in Kleinia articulata.— J. exp. Bot. 38: 1741–1755. The long-day-induced senescence in Kleinia articulata leaveswas characterized by a loss in fresh and dry weight, in therate of leaf expansion and progressive loss of chlorophyll inthe detached rooted leaves. Ultrastructural examination of mesophyllcells of leaves from plants grown in continuous light showedthat osmiophilic globules accumulating in the chloroplasts werethe first visible sign of senescence in the organdies. Thesefirst signs of senescence could be detected in very young leavesof plants in continuous light, even before the leaves had expanded.Attempts were made to study the cause of this photoperiodicsenescence which, from previous work, appeared to involve agraft-transmissible substance. Leaves in continuous light showed reduced stomatal opening andextracts from them had very much higher activity in the Commelinastomatal closure assay (ABA-like activity ?) compared with non-senescingleaves grown in short days (8 h). However, even if all the activitywere due to ABA, this on its own does not appear to be the senescencesubstance because a much longer exposure to continuous lightwas required to induce irreversible senescence than to reachmaximum stomatal closure promoting activity in the bioassay.Moreover, severe water stress (high ABA?) did not lead to senescenceunless combined with continuous light or ethylene treatment.It is postulated that while ABA may play an important role inKleinia leaf senescence its lethal effect may not be realizedunless ethylene-induced membrane changes may synergisticallyassist. Key words: Leaf senescence, ABA, Daylength, stomatal movement, Kleinia     

Water Stress Reduces Ozone Injury via a Stomatal Mechanism

Various studies have shown that water-stressed plants are more tolerant of ozone exposures than are unstressed plants. Two probable explanations for this tolerance are (a) stomatal closure which reduces ozone uptake and (b) biochemical or anatomical changes within the leaves. Phaseolus vulgaris cv Pinto bean plants were established and transferred to membrane systems which controlled the osmotic potential around the roots at −35 or −80 kilopascals for 5 days prior to ozone treatment (0 or 1.0 microliters per liter for 2 hours). Both water-stressed and unstressed plants were sprayed with various concentrations of abscisic acid to close the stomata or with fusicoccin to induce stomata opening. The abaxial stomatal resistances of primary and trifoliate leaves were measured just prior to ozone exposure. Plant response to ozone was determined by stress ethylene production and chlorophyll loss. Both water stress and abscisic acid induced stomatal closure and reduced ozone injury. In water-stressed plants, fusicoccin induced stomatal opening and those plants were as sensitive to ozone as were the non-water-stressed plants. These data suggest that water stress protects plants from ozone injury mainly through its influence on stomatal aperture rather than through biochemical or anatomical changes.     

Effects of iron chlorosis and iron resupply on leaf xylem architecture, water relations, gas exchange and stomatal performance of field-grown peach (Prunus persica)

There is increasing evidence suggesting that iron (Fe) deficiency induces not only leaf chlorosis and a decline of photosynthesis, but also structural changes in leaf morphology, which might affect the functionality of leaves. In this study, we investigated the effects of Fe deficiency on the water relations of peach ( Prunus persica (L.) Batsch.) leaves and the responses of previously chlorotic leaves to Fe resupply via the root or the leaf. Iron deficiency induced a decline of maximum potential photosystem II (PSII) efficiency (F _V/F _M), of rates of net photosynthesis and transpiration and of water use efficiency. Iron chlorosis was associated with a reduction of leaf xylem vessel size and of leaf hydraulic conductance. In the course of the day, water potentials in chlorotic leaves remained higher (less negative) than in green leaves. In chlorotic leaves, normal stomatal functioning was disturbed, as evidenced by the lack of opening upon withdrawal of external CO₂ and stomatal closure after sudden illumination of previously darkened leaves. We conclude that the Fe deficiency induced limitations of xylem conductivity elicited a water saving strategy, which poses an additional challenge to plant growth on high pH, calcareous soils. Fertilisation with Fe improved photosynthetic performance but the proper xylem structure and water relations of leaves were not fully restored, indicating that Fe must be available at the first stages of leaf growth and development.     

Stomatal responses to changing irradiance in Phaseolus vulgaris L.

The effects of air temperature (T_o), leaf-air vapour pressuredifferences [VPD) and water deficit on stomatal responses tochanging irradiance were studied in Phaseolus vulgaris L. Responseswere approximately sigmoidal, with rates of closure being fasterthan the rates of opening. The mean half-time for closure was5.4 min and for the opening 9.2 min. Under water deficit, bothstomatal opening and closing were faster than in well-wateredconditions. Stomata were more sensitive to VPD and water stressthan to T_o. The higher the VPD or T_o the more rapid was thestomatal response, except in stressed plants where there wasno significant effect of T_o. Under water stress, stomata weremore sensitive to water potential (     

Inhibition of photosynthesis in olive trees (Olea europaea L.) during water stress and rewatering

The effect of high levels of natural light on leaf photosynthesisin olive trees (Olea europaea L. var. Coratina), grown in potsoutdoors in the summer and subjected to water, stress, was studied.Net photosynthetic rates reached maximum values early in themorning in both control and stressed plants and subsequentlydeclined gradually. This inactivation of photosynthetic activitywas accompanied by changes in the fluorescence characteristicsof the upper intact leaf surface. The maximum fluorescence yield(Fp) and the ratio Fv/Fp decreased at midday especially in water-stressedplants, but the initial fluorescence (Fo) rose to a maximumvalue at midday and declined again in the afternoon. In controlplants the values of maximum fluorescence Fp and the ratio Fv/Fpincreased again in the afternoon and had recovered almost completelyby 8 p.m. as the leaf water potential recovered. In stressedplants this diurnal recovery was not complete, so that the photosyntheticrates and the ratio Fv/Fp declined gradually during the developmentof water stress. These results indicate that in olive treessubjected to severe water stress the non-stomatal componentof photosynthesis was affected and perhaps a light-dependentinactivation of the primary photochemistry associated with photosystemII (PSII) occurred. Four to five days after rewatering severelystressed plants, the predawn leaf water potential, net photosyntheticrates and chlorophyll fluorescence indices recovered only partially. Key words: Olea europaea, photosynthesis, water stress, chlorophyll a fluorescence, inhibition of photosynthesis     

Inhibition of stomatal opening in sunflower leaves by carbon monoxide,and reversal of inhibition by light

When leaves of Helianthus annuus, whose stomates had been opened in the dark in the absence of CO₂, were exposed to 25% carbon monoxide (CO), stomatal conductivity for water vapor decreased from about 0.4 to 0.2 cm·s^-1. The CO effect on stomatal aperture required a CO/O₂ ratio of about 25. As this ratio was decreased the stomata opened, indicating that inhibitio of cytochrome-c oxidase by CO is competitive in respect to O₂. Photosynthetically active red light was unable to reverse CO-induced stomatal closure even at high irradiances, when CO₂ was absent. When it was present, stomatal opening was occasionally, but not consistently observed. Carbon monoxide did not inhibit photosynthetic carbon reduction in leaves of Helianthus.In contrast to red light, very weak blue light (405 nm) increased the stomatal aperture in the presence of CO. It also increased leaf ATP/ADP ratios which had been decreased in the presence of CO. The blue-light effect was not related to photosynthesis. Neither could it be explained by photodissociation of the cytochrome a ₃-CO complex which has an absorption maximum at 430 nm. The data indicate that ATP derived from mitochondrial oxidative phosphorylation provides energy for stomatal opening in sunflower leaves in the dark as well as in the light. Indirect transfer of ATP from chloroplasts to the cytosol via the triose phosphate/phosphoglycerate exchange which is mediated by the phosphate translocator of the chloroplast envelope can support stomatal opening only if metabolite concentrations are high enough for efficient shuttle transfer of ATP. Blue light causes stomatal opening in the presence of CO by stimulating ATP synthesis.     

Responses of Stomata to IAA and Fusicoccin at the Opposite Phases of an Entrained Rhythm

The stomata of Commelma communis showed reduced opening responsesto light and low CO₂ concentrations during the night phase oftheir entrained circadian rhythm. Increased supplies of potassiumions, and treatments with indol-3-ylacetic acid and fusicoccin,failed to promote opening during the night phase to a levelequivalent to that in the day phase. The inability of fusiccocinto overcome the suppression of opening during the night phasecontrasts with its ability to counteract the closure inducedby agents such as CO₂, darkness and abscisic acid. It is concludedthat there are at least two basic mechanisms by which the turgorof guard cells can be regulated, one which is susceptible tooverriding control by fusicoccin and another which is unaffectedby fusicoccin. Several previous studies had shown a positive correlation betweenmalate in the epidermis (mainly located in guard cells) andstomatal opening. In the present experiments the aperture/malatecorrelation was broken in epidermis treated with fusicoccinduring the night phase of the rhythm. The amount of malate presentexceeded that associated with the same stomatal aperture inthe day phase. Possible explanations are (1) that fusicoccinstimulates similar proton fluxes out of the guard cells duringboth phases of the rhythm, but an unknown factor imposes a restrictionon stomatal opening during the night phase; (2) that there arelower proton fluxes in the night phase (limited, for example,by a reduced supply of ATP) but chloride availability or transportis reduced to an even greater extent so that a larger productionof malate in the guard cells is required. Key words: Stomata, IAA, Fusicoccin, Rhythms     

Potassium Deficiency-induced Changes in Stomatal Behavior, Leaf Water Potentials, and Root System Permeability in Beta vulgaris L

Studies of the water relations of potassium deficient sugarbeet plants (Beta vulgaris L.) revealed two factors for stomatal closure. One component of stomatal closure was reversible by floating leaf discs on distilled water to relieve the water deficit in the leaves; the other component was reversible in the light by floating the leaf discs on KCl solution for 1 hour or more. Potassium-activated stomatal opening in the light was observed when the guard cells were surrounded by their normal environment of epidermal and mesophyll cells, just as observed by previous workers for epidermal strips. Leaf water potentials, like stomatal apertures, appear to be strongly related to leaf potassium concentration. Potassium-deficient plants have a greatly decreased root permeability to water, and the implications of this effect on stomatal aperture and leaf water potential are discussed. In contrast, petiole permeability to water is unaffected by potassium treatment.     

Effect of Cuticular Abrasion on Thermocouple Psychrometric In Situ Measurement of Leaf Water Potential

Cuticular resistance to water vapour diffusion between the substomatalcavity and the sensing psychrometer junction is a problem uniqueto leaf hygrometry. This resistance is not encountered in soilor solution hygrometry. The cuticular resistance may introduceerror in the measurement of leaf water potential. Using in situleaf hygrometers, we studied the effect of abrading the cuticleof Citrus jambhiri Lushington leaves, to reduce the diffusiveresistance. Field measurements of psychrometer water potentialwere compared with Scholander pressure chamber values for adjacentleaves. Different treatments were compared by sealing pairsof psychrometers on either side of the midrib. The time forwater vapour equilibration between the leaf and the psychrometerchamber was greater than 5 h for no abrasion. For abraded leaves,the true water potential value was obtained within an hour.After equilibration, psychrometer values compared favourablywith pressure chamber values for adjacent leaves (r > 0.97).Measured water potential for unabraded leaves did not correlatewell with corresponding pressure chamber measurements. Scanning electron micrographs indicated that the damage causedby abrading leaves for 60 s using carborundum powder (60 µmdiameter) was surface localized, with numerous scratchings ofthe leaf cuticle. The coarse abrasion treatment (aluminium oxide,75 µm diameter) resulted in fewer but larger cavitiesin the epidermis, which may explain the observed variabilityin the corresponding psychrometric measurements. Key words: Leaf water potential, Cuticular resistance, Leaf abrasion, Thermocouple psychrometer     

Manometric Measurement of Turgor Pressures in Laticiferous Phloem Tissues2

A manometric technique for the determination of turgor pressuresin laticiferous phloem tissues has given reproducible resultsin Hevea brasiliensis and a few other tree species. In Hevea,early morning pressures are in the range 7.9–15.0 atmospheres,falling during the day and recovering at night. These diurnalpressure changes are positively correlated with atmosphericrelative humidity and negatively correlated with changes intemperature, evaporation, leaf water deficit, and stomatal opening.They are not displayed by trees devoid of leaves. Thus the lossin turgor is probably the result of withdrawal of water fromthe phloem tissues under transpirational stress. Pressures at the base of the trunk normally exceed those atthe top, the gradient usually approximating to 1 atmosphere/10metres at night and rising up to six times this figure duringthe day. This increase probably reflects the development oftension gradients in the xylem during transpiration. A generalturgor gradient from base to crown does not preclude mass flowin sieve-tubes in the opposite direction provided that ratesof loading and unloading are such that a sufficient osmoticgradient is maintained in them in the required direction. No marked long-term effects of regular tapping on turgor pressurehave been noted in Hevea trees and there is no evidence forseasonal changes in turgor under our conditions.     

Positive and Negative Messages from Roots Induce Foliar Desiccation and Stomatal Closure in Flooded Pea Plants

Flooding the soil for 5–7 d caused partial desiccationin leaves of pea plants (Pisum sativum. L. cv. ‘Sprite’).The injury was associated with anaerobiosis in the soil, a largeincrease in the permeability of leaf tissue to electrolytesand other substances, a low leaf water content and an increasedwater saturation deficit (WSD). Desiccating leaves also lackedthe capacity to rehydrate in humid atmospheres, a disabilityexpressed as a water resaturation deficit (WRSD). This irreversibleinjury was preceded during the first 4–5 d of floodingby closure of stomata within 24 h, decreased transpiration,an unusually large leaf water content and small WSD. Leaf waterpotentials were higher than those in well-drained controls.Also, there was no appreciable WRSD. Leaflets detached fromflooded plants during this early phase retained their watermore effectively than those from controls when left exposedto the atmosphere for 5 min. Stomatal closure and the associated increase in leaf hydrationcould be simulated by excising leaves and incubating them withtheir petioles in open vials of water. Thus, such changes inflooded plants possibly represented a response to a deficiencyin the supply of substances that would usually be transportedfrom roots to leaves in healthy plants (negative message). Ionleakage and the associated loss of leaf hydration that occurswhen flooding is extended for more than 5 d could not be simulatedby isolating the leaves from the roots. Appearance of this symptomdepended on leaves remaining attached to flooded root systems,implying that the damage is caused by injurious substances passingupwards (positive message). Both ethylene and ethanol have beeneliminated as likely causes, but flooding increased phosphorusin the leaves to concentrations that may be toxic. Key words: Pisum sativum, Flooding, Foliar desiccation, Stomata, Ethylene     

In situ observations of stomatal movements in different light-dark regimes: the influence of endogenous rhythmicity and long-term adjustments

The technical device for continuous microscopic observationsof stomatal movements in a gas exchange chamber using digitalimage analysis, earlier described by Kappenet al. (1994), wastechnically improved. By electronic remote control, it is nowpossible repeatedly to record over a period of several daysidentical stomata on a 25 50 mm leaf area. The responses ofindividual stomata to various light-dark sequences in the lightand in the dark phase were investigated on attached leaves ofViciafaba (L.). The amplitude of stomatal oscillations caused byalternatinglight was highest on the first day of an experimental seriesand decreased with repeated application, indicating a long-termadjustment to changing light conditions by decreasing sensitivityto intermittent darkening. In the usual dark phase light-darksequences had little effect on the stomatal aperture, whichremained small. These results were widely convergent with thestomatal conductance calculated from the gas exchange measurements.Very prominent is the role of an endogenous rhythmicity of thestomatal response. It could be demonstrated (1) by autonomousstomatal opening before the light phase started; (2) by a suppressionof dark response in the early morning hours; (3) by a decreasinglight stimulation in the afternoon; (4) by further increaseof aperture for several hours if no light was provided in thelight phase. Closely adjacent stomata could show divergent dark-openingmovements pointing to an autonomous control mechanism locatedin the guard cells. The endogenously controlled morning openingprovides full assimilation capacity in the usually humid morninghours when transpiratory water loss associated with C02-uptakeis comparatively small. Key words: Stomata, changing PPFD, desensitization, endogenous rhythmicity, diurnal courses, Vicia faba     

Water Relations of Tropical Epiphytes: III. EVIDENCE FOR CRASSULACEAN ACID METABOLISM

Five tropical epiphytes were examined for evidence of CrassulaceanAcid Metabolism (CAM), namely the orchids Eria velutina Lindl.,Dendrobium tortile Lindl. and Dendrobium crumenatum Sw., andthe ferns Pyrrosia adnascens (Forst.) Ching and Pyrrosia angustata(Sw.) Ching, family Polypodiaceae. Diurnal variations in leaftitratable acidity, diffusive conductance and water potentialwere measured at various levels of water stress. The three orchidsshowed typical CAM behaviour, namely large diurnal fluctuationsin leaf acidity, day-time closure and night opening of stomataand a very slow decline in water potential under stress. Theferns showed some evidence of CAM, but this was not as well-developedas had been reported for two other tropical epiphytic membersof the same family. Key words: Crassulacean acid metabolism, Tropical epiphytes, Water stress