Loss of Stomatal Function in Ageing Hybrid Poplar Leaves

Under a variety of conditions old, non-senescent hybrid poplar(Populus sp.) leaves exhibited less stomatal control than young,mature leaves. Stomata of older leaves displayed oscillatorybehaviour more frequently, and oscillations were more random,than in younger leaves. Also, diffusive conductance of olderleaves changed less following sudden shifts from either darkto light, or vice versa, than in younger leaves, and temporalpatterns of diffusive conductance in older leaves appeared tobe relatively independent of microenvironmental conditions.Levels of conductance of older leaves were higher both in thedark and following excision than in younger leaves, while inthe light the situation was reversed. Total range of responseand stability of diffusive conductance were also lower in olderrather than in younger leaves. All of the observed age-relateddifferences suggest a loss of stomatal control with increasingleaf age. Leaf age, Populus sp., stomatal cycling, stomatal function, hybrid poplar     

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     

Effects of irradiance and leaf water deficit on net carbon dioxide assimilation and mesophyll and transport resistances

Rate of net CO₂ assimilation by soil-grown soybean plants were studied over a range of relative leaf water contents at each of four levels of irradiance. There was a large interaction between light level and leaf water deficit on the rate of CO₂ assimilation. The effect of leaf water deficit on assimilation became larger as irradiance increased. Both stomatal resistance to CO₂ transport and mesophyll resistance to CO₂ assimilation increased as leaf-water deficit increased. The increase in both resistance with changing leaf-water content was largest at high irradiance and became smaller as irradiance decreased. Relief of soil-moisture stress by watering induced large oscillations of CO₂ assimilation, stomatal resistance, and mesophyll resistance. The oscillation of the mesophyll resistance occurred in the absence of changes in relative water content and appeared to be related to oscillations in leaf temperature. The observed increase in mesophyll resistance with decreasing leaf-water content under nonoscillative conditions may be caused by changes in leaf temperature rather than leaf water content.     

Tentoxin Suppresses Stomatal Opening by Inhibiting Photophosphorylation

Tentoxin and, to a lesser extent, dihydrotentoxin (both at 10mmol m^–3) reduce stomatal opening in epidermal stripsof Commelina communis in the light but not in darkness. Thiseffect was significantly greater in normal air than in CO₂-freeair. Fusicoccin overcame the tentoxin effect. However, tentoxindid not inhibit stomatal opening in the light in epidermal stripsof Paphiopedilum harrisianum, a species which lacks guard cellchloroplasts. It is concluded that tentoxin exerts its actionon stomata not by an ionophorous effect in the plasmalemma ofguard cells but by the inhibition of photophosphorylation intheir chloroplasts. The effects of DCMU and tentoxin on guardcells are discussed in terms of their effects on chloroplastsand the extent to which energy is supplied from this organelleduring stomatal opening in the light. The results indicate thatneither photophosphorylation nor non-cyclic electron transportin guard cell chloroplasts are essential for stomatal opening. Key words: Commelina, epidermal strips, Paphiopedilum, photophosphorylation, stomata, tentoxin     

Effect of Wind on the Transpiration of Young Trees

The effects of wind on the transpiration rates of four plantspecies, Pinus sylvestris L., Quercus robur L., Fagus sylvaticaL. and Sorbus aucuparia L., were studied in a controlled environmentwind tunnel. Transpiration declined with increasing wind speedin a manner consistent with predictions of the Penman-Monteithequation. The stomatal resistance declined with increasing windspeed in two species and increased in one, but this effect wassmaller than reported in other studies. In all cases the magnitudeof the stomatal response was over-shadowed by the decliningleaf to air vapour pressure difference. Pinus sylvestris L., Quercus robur L., Fagus sylvatica L., Sorbus aucuparia L., wind, transpiration, cooling curve technique, stomatal resistance, aerodynamic resistance, Penman-Monteith equation     

Stomatal Response of some Cultivated and Wild Tuber-bearing Potatoes in Warm Tropics as Influenced by Water Deficits

Leaf resistances of 14 cultivated potato genotypes (Solanumspp) and three tuber-bearing wild Solanum species were comparedwhen plants were grown under water stress at two tropical sitesFactors investigated were diurnal changes in leaf resistance,the effect of plant age, transient drought versus well-wateredconditions of potted and field-grown plants These measurementswere carried out in order to determine the stomatal behaviourof tuber-bearing genotypes and species Significant genotypic differences in leaf resistances were notedwithin the cultivated genotypes All genotypes had higher resistanceswhen water-stressed, but LT-7 appeared to have the lowest leafresistances Genetic differences in stomatal behaviour of tuber-bearingSolanum species were confirmed Abaxial stomatal resistancesof water-stressed plants of the species ranged between 1 74and 13 8 s cm^–1 Stomata of S chacoense were less affectedby drought (three-fold) than S tuberosum (four-fold) The greatesteffect was on S jungasense (five-fold) and on S raphanifoliumThese data show that stomata behaviour among tuber-bearing Solanumspecies is sufficiently different to warrant investigationsof drought-resistance in potato species under dry hot conditions Solanum tuberosum L., Solanum raphanifolium, Solanum chacoense, Solanum jungasense, leaf resistance     

Characterization of a wilty sunflower (Helianthus annuus L.) mutant: III. Phenotypic interaction in reciprocal grafts from wilty mutant and wild-type plants

The present study was conducted to evaluate phenotypic interactionin reciprocal grafts between wilty (w-1) sunflower mutant andnormal (W-1) plants. The w-1 genotype is a ‘leaky’ABA-deficient mutant, characterized by high stomatal conductance,in both light and dark conditions, and high transpiration rate. In well-watered conditions, mutant scions grafted on to normalrootstock (w-1/W-1) showed higher leaf relative water content,leaf water potential and ABA levels than those of control grafts(w-1/w-1). In addition, detached leaves of w-1/W-1 exhibitedlower water loss than w-1/w-1 grafts, while mutant rootstockdid not affect the transpiration rate of detached W-1 leaves.When drought stress was imposed to potted plants by withholdingwater, the mutant scions grafted on to normal roots showed apartial phenotypic reversion. A rapid stomatal closure and arise in ABA levels in response to a small decrease in leaf waterpotential was observed. By contrast, in w-1/w-1 grafts significantreductions in stomatal conductance and ABA accumulation weredetected only in conjunction with a severe water deficit. W-1scions on mutant stocks (W-1/w-1) maintained the normal phenotypeof control wild-type grafts (W1/W-1). Key words: ABA, grafting, Helianthus annuus, stomatal conductance, water relations, wilty mutant     

Oscillations in Extracellular Current, External pH and Membrane Potential and Conductance in the Alkaline Bands of Nitella and Chara

Oscillations with a period of approximately 2 min were observedin the membrane potential of Chara and Nitella upon illuminationof dark-treated cells, as well as in the extracellular currentpattern and pH values. A 2-min oscillation in the membrane potentialwas observed when the voltage electrode was placed close tothe border of an alkaline and acid region. Comparison of resultsfrom Chara and Nitella revealed an identical control mechanismfor external pattern stabilization in the effect of light onmembrane potential and conductance. Vibrating probe experimentsindicated that oscillations in the extracellular current occurredonly at the border of the alkaline band. Ion-specific pH micro-electrodesplaced within the alkaline band detected oscillations associatedwith light reactivation of the banding phenomenon. These resultsindicate that the oscillations represent a localized phenomenoninvolving spatially-dependent time-constants. More evidencefor the spatial dependence of time constants is gained fromsingle active acid regions in Nitella. Using this combinationof techniques, we have established that a light-dependent H⁺transporter is involved in this oscillation. Current-voltagecurves taken during these oscillations and relaxation, afterchanging the light intensity, confirmed this identification. Key words: Oscillation, vibrating probe, pH micro-electrode, time-constant. I/V curve, Chara, Nitella     

The Responses of Net Photosysthesis to Light and Temperature in Spartina townsendii(sensu lato), a C4 Species from a Cool Temperate Climate

Carbon dioxide and water vapour exchanges for single attachedleaves of the temperate C₄ grass Spartina townsendii were measuredunder controlled environment conditions in an open gas-exchangesystem. The responses of net photosynthesis, stomatal resistance,and residual resistance to leaf temperature and photon fluxdensity are described. The light and temperature responses ofnet photosynthesis in S. townsendii are compared to informationon these responses in both temperate C₃ grasses and sub-tropicalC₄ grasses. Adaptation of photosynthesis in this C₄ speciesto a cool temperate climate is indicated both by the light andtemperature responses of net photo-synthesis. Unlike the C₄grasses examined previously, significant rates of net photosynthesiscan be detected at leaf temperatures below 10?C. Rates of netphotosynthesis equal or exceed those reported for temperateC₃ grasses at all of the temperature (5–40?C) and photonflax density (13–2500µmol m^–2 s^–1) conditionsexamined. Maximum rates of net photosynthesis in S. townsendiiare almost double those reported for C₃ herbage grasses. Unliketemperate C₃ grasses, the major limitation to net photosynthesisat low leaf temperatures (10?C and below) is the stomatal resistance,showing that the low residual resistance characteristic of C₄species is maintained in S. townsendii even at low leaf temperatures.     

A Radioactive Tracer Technique for the Direct Measurement of the Diffusion Resistance of Stomata

A new method is described for measuring the stomatal resistanceto diffusion in leaves. It consists of measuring the radioactivityof air samples which have diffused through a leaf from a porometercontainer enriched with radioactive argon(⁴¹A). Details of thecalibration are given together with the methods adopted to determinethe accuracy of measurement and the optimum time of sampling.Results suggest that in the material investigated the measurementsobtained are essentially those of stomatal resistance.In onesmall experiment inter and intra plant variability in stomatalresistance was investigated; in another, the diffusion porometerwas used to compare the daily march of stomatal resistance withthe rate of transpiration in plants growing under four differentsoil-moisture regimes.     

The Partitioning of Resistances to Gaseous Diffusion in the Leaf Epidermis and the Boundary Layer

The partitioning of total leaf resistance to gaseous diffusioninto the cuticular, stomatal, and boundary-layer componentsof the upper and lower leaf surfaces was studied. A generalformula was developed, which showed that the mean stomatal oreven mean epidermal resistances may not be obtained by simplesubtraction of the boundary-layer component from the total,except in very specific cases. The formula was used to studythe relationship between the mean stomatal resistance, _s, and the residual leaf resistance, r_l (obtainedby subtracting the boundary-layer from the total resistance),in leaves differing in their degree of anisolaterality (withrespect to stomatal resistance), cuticular resistance, and totalresistance, as affected by the relative magnitude of the boundary-layercomponent. Graphical presentation of the analyses permits evaluationof the difference between _s, and r_l in awide variety of cases. It was shown experimentally that whenthe stomatal component of each leaf surface is known, the totalresistance calculated from these values according to the formulaclosely matches the measured value.     

The Comparative Effects of Blue and Red Light on the Stomata of Allium cepa L. and Xanthium pennsylvanicum

Stomatal responses to blue and red light were compared in leavesof Xanthium pennsylvanicum (which contain starch in their guardcells) and in onion leaves (which are devoid of starch). Bluelight was found to be more effective than red in opening stomatain both species. However, a significant difference in the ratiosof blue to red light required to produce equal stomatal openingwas found between Xanthium pennsylvanicum and onion. It is concludedthat blue light may promote stomatal opening by its effect onenzymes controlling the starch and soluble polysaccharide contentof guard cells.     

Effects of Different CO2 Environments on the Photosynthesis-Yield Relationship and the Carbon and Water Balance of a White Clover (Trifolium repens L. cv. Blanca) Sward

Effects of atmospheric CO₂ enrichment to a level above 600 parts10^–6 on leaf and canopy gas exchange characteristics wereinvestigated in Trifolium repens, using an open system for gasexchange measurement. The cuvettes of the system served as growthchambers, allowing continuous measurement in a semi-controlledenvironment of ±350 and ±600 parts 10^–6CO₂, respectively. Carbon balance data were compared with cropyield and effects on the canopy level were compared with measuredleaf responses of photosynthesis and stomatal behaviour. Photosyntheticstimulation by high CO₂ was stronger at the canopy level (103%on average) than for leaves (90% in full light), as a consequenceof accelerated foliage area development. The latter increasedabsolute water consumption by 16%, despite strong stomatal closure.The overall result was a 63% improvement in canopy water useefficiency (WUE), while leaf WVE increased almost 3-fold insaturating light. The stomatal response was such that, whilethe internal CO₂ concentration in the leaf, ch increased withrising atmospherical CO₂ concentration, c_a, ci/c_a was somewhatdecreased. Total canopy resistance, R_c, was generally lowerat high CO₂ levels, despite higher leaf resistance. Higher canopyCO₂ loss at night and faster light extinction in a larger-sizedhigh CO₂ canopy were major drawbacks which prevented a furtherincrease in dry matter production (the harvest index was increasedby a factor 1.83). Key words: CO₂ enrichment, canopy CO₂ exchange, carbon balance, water use efficiency, leaf and canopy resistance     

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.     

The Influence of Prior Water Stress and Abscisic Acid Foliar Spraying on Stomatal Responses to CO2, IAA, ABA, and Calcium in Leaves of Solanum melongena

The influence of a water stress or foliar ABA spraying pretreatmenton stomatal responses to water loss, exogenous ABA, IAA, Ca²⁺,and CO₂ were studied using excised leaves of Solanum melongena.Both pretreatments increased stomatal sensitivity of water loss,in the presence and absence of CO₂, but decreased stomatal sensitivityto exogenous ABA. CO₂ greatly reduced the effect of exogenouslyapplied ABA. IAA decreased leaf diffusion resistance for controland ABA sprayed leaves, but did not influence the LDR of previouslywater-stressed leaves. CA²⁺ did not influence LDR of any leavesof any treatments. Key words: Water stress, stomatal response, pretreatments     

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     

The Responses of Net Photosynthesis to Vapour Pressure Deficit and CO2 Concentration in Spartina townsendii (sensu lato), a C4 Species from a Cool Temperate Climate

As the initial part of a detailed study of photosynthetic CO₂assimilation in the temperate C₄ grass, Spartina townsendii,the responses of net photosynthesis to the leaf-air vapour pressuredeficit (VPD) and to CO₂ concentration are examined. Water vapourand CO₂ exchange for single attached leaves were measured undercontrolled-environment conditions in an open gas-exchange system.The responses of net photosynthesis, stomatal resistance (r_s),and residual resistance (r_r) to vapour pressure deficit(VPD)and CO₂ concentration under a range of light and temperatureconditions are reported. Net photosynthesis was insensitiveto increase in the VPD up to 1.0 kPa, but beyond this valuenet photosynthesis decreased with further increase in VPD asa result of an increase in r_s. The residual resistance was notaffected by VPD under any of the conditions examined. Net photosynthesisresponded linearly to increase in the CO₂ concentration in theexternal air (C_a up to the normal atmospheric concentrationwhere there was a sharp change in the response, net photosynthesisbeing independent of any further increase in C_a. Differencesbetween the response curves observed here and in other studiesare discussed and the possible reasons for these differencesare considered.     

Changes in stomatal movements in isolated epidermal strips of a CAM plant, Notonia grandiflora DC

The diuranl rhythm of the stomatal aperture size was investigatedusing isolated epidermal strips from a CAM plant, Notonia grandiflora.Maximal stomatal opening occurred at pH 6.5. The nocturnal stomatalopening was stimulated by KCl which produced stomatal closurein light. The stimulatory effect of KCl on stomatal openingin drakness was suppressed by ABA. (Received January 24, 1978; )     

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.     

A three-dimensional model of CO2 transport in airspaces and mesophyll cells of a silver birch leaf

A realistic numerical three‐dimensional (3D) model was constructed to study CO₂ transport inside a birch leaf. The model included chloroplasts, palisade and spongy mesophyll cells, airspaces, stomatal opening and the leaf boundary layer. Diffusion equations for CO₂ were solved for liquid(mesophyll) and gaseous(air) phases. Simulations were made in typical ambient field conditions varying stomatal opening, photosynthetic capacity and temperature. Doubled ambient CO₂ concentration was also considered. Changes in variables caused non‐linear effects in the total flux, especially when compared with the results of double CO₂ concentration. The reduction in stomatal opening size had a smaller effect on the total flux in doubled concentrations than ambient CO₂. The reduced photosynthetic capacity had a similar effect on the flux in both cases. The palisade and spongy mesophyll cells had unequal roles mainly due to the light absorption profile. Results from the 3D simulation were also compared to the classical one‐dimensional resistance approach. Liquid and gas phase resistances were estimated and found strongly variable according to changes in temperature and degree of stomatal opening. For the birch leaves modelled, intercellular airspace resistance was small (2% of the total resistance in saturating irradiance conditions at 25 °C at stomatal opening diameter of 4 µm) whereas the liquid phase resistance was significant (23% for mesophyll and chloroplasts in the same ‘base case’). The absorption of CO₂ into water at cell surfaces caused additional (strongly temperature dependent) resistance which accounted for 36% of the total resistance in the base case.