Effect of Source-Sink Manipulations on the Crassulacean Acid Metabolism of Kalanchoe pinnata

The effect of manipulations of the sink-source at the above-groundlevel and girdling of source leaves was measured in 4-month-oldplants of the CAM species Kalancho pinnata (Lam.) Pers. At thisage plants developed five pairs of leaves. The upper fourthand fifth leaf pairs were not fully expanded and behaved ascarbohydrate sinks. Removal of the developing leaves induceda progressive accumulation of glucans and sugars in the matureleaves. The titratable acidity increased during the second weekbut accumulation was less than in the control plants three tofour weeks after sink removal. Similar, but more rapid, resultswere observed in mature leaves with girdled petioles. Up tothe second night after girdling dark CO₂ fixation increased,but decreased steadily afterwards. CAM Phase 4 (afternoon CO₂fixation) however, was more sensitive to girdling, being reducedby 38% on the first day, and disappearing completely 3 d aftergirdling. The glucan and sugar contents of girdled leaves increasedcontinuously after treatment, but day-night changes ceased completelyon the fifth day. Girdling also caused a considerable increasein chloroplast area, with up to 80% of their internal spaceoccupied by starch grains, leading to grana distortion. In girdledleaves, or in source leaves in plants lacking aerial carbohydratesinks, dawn-dusk changes in titratable acidity started to decreasewhen the leaf glucan content exceeded 1·0 mol equivalenthexoses kg^–1 dry weight. Increased sink strength throughshading of all leaves except one source leaf did not affectits CAM activity. The titratable acidity and non-structuralcarbohydrate content of the shaded mature leaves was reducedby around 55%. Removal of all the mature source leaves acceleratedthe maturation process of sink leaves, increasing titratableacidity at dawn and synthesis of glucans during the light period.The results support the hypothesis that CO₂ fixation in a CAMplant is controlled by accumulation of glucans in chloroplasts. Key words: CAM, glucan accumulation, sink-source ratio, CO₂ fixation     

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.     

Stomatal Responses to Water Deficits and Abscisic Acid in Leaves of Sunflower Plants (Helianthus annuus L.) Grown under Different Conditions

The decrease in diffusive conductance of a leaf exposed to waterstress or to exogenous abscisic acid (ABA) was smaller in leavesof sunflower plants (Helianthus annuus L. cv. NK285) that hadbeen grown in a phytotron in humid air than in leaves of sunflowersgrown outdoors. Stomata of the phytotron-grown plants were slowerto close after detachment of a leaf than those of the outdoorplants. When stomata closed rapidly, as they did in detachedleaves and after treatment with ABA, the extent of closure wasvaried over the leaf's surface, in particular in the case ofphytotron-grown plants, and the extent of the heterogeneitywas greater in the phytotrongrown plants than in the outdoorplants. When stomata closed gradually, for example, under conditionsof limited moisture in the soil, closure occurred uniformlyover leaves of plants of both types. The smaller decrease indiffusive conductance of leaves from phytotron-grown plantsafter treatment with ABA resulted from the presence of patcheson the surface in which stomata remained open. The smaller decreaseof diffusive conductance in the phytotron-grown plants underconditions of limited moisture in the soil resulted from theuniformly lower responsiveness of stomata on a leaf to the decreasein water potential. When estimates are made of the intercellularconcentration of CO₂ (Ci) from gas-exchange measurements, heterogeneityin stomatal closure should be monitored when stomata close rapidly,in particular in plants grown in humid air, because heterogeneousstomatal closure can lead to overestimates of Ci. (Received April 18, 1994; Accepted May 25, 1995)     

Studies in Sieve-tube Exudation through Aphid Mouth-parts: The Effects of Light and Girdling

Exudation from the mouth-parts of the willow aphid Tuberolachnussalignus (Gmelin) inserted in the phloem of Salix sp. was studied.Leafy rooted cuttings 80–100 cm. in length were grownin artificial light. Exuding mouth-parts were located on thestem below the crown of leaves and the rates of exudation andconcentration of sucrose in the exudate measured whilst theleaves were alternately illuminated (600–800 f.c.) anddarkened. In darkness the rate of sap and sucrose exudationincreased and the concentration fell, relative to the valuesin the light. Similar effects were produced by girdling thestem just beneath the crown of leaves. These were shown to besecondary effects due to a lessening of transpirational tensionsduring darkness or after girdling. They were eliminated if changesin water tension were avoided. Direct effects of light and girdling on exudation were demonstratedby allowing the leaves to assimilate ¹⁴CO₂ and measuring thespecific activity of the exudate. These changes in radioactivityseen against the constancy in total sugar exudation demonstratea switch in source from leaf to stem. An attempt is made toexplain the pattern of changes in specific activity of the exudateduring light and dark periods in terms of shifts in the locationof contributing sources. The rate of translocation between two aphid colonies situateda measured distance apart was estimated by noting the timeswhen the honeydew from each reached a certain level of radioactivity.A mean figure of 28 cm./hr. was obtained.     

Separation of Direct and Indirect Responses of Stomata to Light: Results from a Leaf Inversion Experiment at Constant Intercellular CO2 Molar Fraction

Previous work has shown that stomata respond directly to light,but it was not clear whether the only additional response isthrough CO₂, or whether some other metabolite is involved inthis response. Gas exchange experiments were done with normallypositioned and inverted leaves of Hedera helix to investigatethis problem. The macroscopic optical properties of the leavesand their anatomical structure were also studied. These experimentssnowed that there is no need to postulate the existence of amessenger other than CO₂ to explain the indirect response ofstomata to light. The experiments also showed that leaf inversionaffects both stomatal conductance and photosynthesis, and highlightthe difficulties involved in the interpretation of the effectof leaf inversion on stomata when stomatal conductance measurementsare not done concurrently with measurements of CO₂ flux densityand intercellular CO₂ molar fraction Key words: Hedera helix, ivy, gas exchange, leaf inversion, stomatal conductance, light, CO₂ flux density, photosynthesis     

Changing Responses of Stomata to Abscisic Acid and CO2 as Leaves and Plants Age

Willmer, C. M., Wilson, A. B. and Jones, H. G. 1988. Changingresponses of stomata to abscisic acid and CO₂ as leaves andplants age.—J. exp. Bot. 39: 401–410. Stomatal conductances were measured in ageing leaves of Commelinacommunis L. as plants developed; stomatal responses to CO₂ andabscisic acid (ABA) in epidermal strips of C. communis takenfrom ageing leaves of developing plants and in epidermal stripsfrom the same-aged leaves (the first fully-expanded leaf) ofdeveloping plants were also monitored. Stomatal behaviour wascorrelated with parallel measurements of photosynthesis andleaf ABA concentrations. Stomatal conductance in intact leavesdecreased from a maximum of 0-9 cm s^{– 1} at full leaf expansionto zero about 30 d later when leaves were very senescent. Conductancesdeclined more slowly with age in unshaded leaves. Photosynthesisof leaf slices also declined with age from a maximum at fullleaf expansion until about 30 d later when no O₂ exchange wasdetectable. Exogenously applied ABA (0.1 mol m^{– 3}) didnot affect respiration or photosynthesis. In epidermal stripstaken from ageing leaves the widest stomatal apertures occurredabout 10 d after full leaf expansion (just before floweringbegan) and then decreased with age; this decrease was less dramaticin unshaded leaves. The inhibitory effects of ABA on stomatalopening in epidermal strips decreased as leaves aged and wasgreater in the presence of CO₂ than in its absence. When leaveswere almost fully-senescent stomata were still able to open.At this stage, guard cells remained healthy-looking with greenchloroplasts while mesophyll cells were senescing and theirchloroplasts were yellow. Similar data were obtained for stomatain epidermal strips taken from the same-aged leaves of ageingplants. The inhibitory effects of ABA on stomatal opening alsodecreased with plant age. In ageing leaves both free and conjugated ABA concentrationsremained low before increasing dramatically about 30 d afterfull leaf expansion when senescence was well advanced. Concentrationsof free and conjugated ABA remained similar to each other atall times. It is concluded that the restriction of stomatal movements inintact leaves as the leaves and plants age is due mainly toa fall in photosynthetic capacity of the leaves which affectsintracellular CO₂ levels rather than to an inherent inabilityof the stomata to function normally. Since stomatal aperturein epidermal strips declines with plant and leaf age and stomatabecome less responsive to ABA (while endogenous leaf ABA levelsremain fairly constant until leaf senescence) it is suggestedthat some signal, other than ABA, is transmitted from the leafor other parts of the plant to the stomata and influences theirbehaviour. Key words: Abscisic acid, CO₂, Commelina, leaf age, senescence, stomatal sensitivity     

Ethylene Release from Leaves of Xanthium strumarium L. and Zea mays L.

The release of ethylene into sealed Erlenmeyer flasks by intactleaves and leaf discs of Xanthium strumarium L. a C₃ plant andZea mays L. a C₄ plant were compared both in white light andin darkness. The effects of the presence or absence of addedCO₂ (in the form of sodium bicarbonate) the photosynthetic inhibitor3-[3,4-dichlorophenyl]-l, l-dimethyl urea (DCMU) and 1-aminocyclopropane-1-carboxylicacid (ACC), the precursor of ethylene in higher plants, werealso investigated. The rate of ethylene release from leaf tissue of Xanthium inthe absence of added CO₂ was markedly reduced in the light (i.e.at the CO₂ compensation point). Treatments that would enhancethe CO₂ availability to the tissue (i.e. added bicarbonate,darkness, treatment with DCMU) allowed higher levels of ethylenerelease. Incubation of the tissue with ACC considerably enhancedthe release of ethylene compared to that from the correspondingcontrol tissue without ACC. However, the pattern of ethylenerelease induced by the various treatments was similar with orwithout added ACC. When tissue, in the absence of added CO₂, was transferred fromlight to darkness, and back to light for 90 min periods, theethylene release rates Increased during the interposed darkperiod but resumed the lower rate during the final light period.The addition of CO₂ in the light resulted in a similar rateof ethylene release to that found in the dark. The overall pattern of ethylene release from Zea leaf tissuesubjected to light and dark in the presence or absence of addedCO₂ was similar to that of Xanthium. However, two or three timesmore ethylene was released from maize leaves in the light whenCO² was added compared to that generated in the dark. This isin marked contrast to Xanthium, where, under the light conditionsused, the ethylene release rate in the dark equalled or exceededthat occurring in the light, even in the presence of high levelsof CO₂. A very low rate of ethylene release was observed atthe CO₂ compensation point of maize. A speculative model is presented to explain how photosyntheticactivity might act as a key factor in regulating ethylene evolutionfrom leaf tissue in these experiments. It invokes the conceptof an inhibition by CO₂ of ethylene retention or breakdown thuspermitting more ethylene to be released from the leaves.     

Changes in Photosynthetic Capacity in Rice Leaves from Emergence through Senescence. Analysis from Ribulose-1,5-bisphosphate Carboxylase and Leaf Conductance

Changes in the rates of gas exchange and the amount of ribulose1,5-bisphosphate (RuBP) carboxylase protein were determinedin the 12th leaf blades of rice during the reproductive stages.RuBP carboxylase exhibited a large change similar to that inthe assimilation rate at 2% O₂ throughout the leaf's life, butits decrease during senescence was barely faster than the decreasein the assimilation rate. Consequently, the overall relationshipwas slightly curvilinear. By contrast, leaf conductance decreasedmore slowly than the assimilation rate which resulted in theintercellular CO₂ concentration increasing during senescence. In order to determine the maximum activity of RuBP carboxylaseat the intercellular CO₂ concentration, the kinetic parametersand their pH response were determined using purified, and completelyactivated, rice RuBP carboxylase. The maximum carboxylase activityat the intercellular CO₂ concentration was linearly correlatedwith the assimilation rate at 2% O₂ (r=0.989), and was veryclose to that needed to account for the assimilation rate. We conclude that changes in both the amount of RuBP carboxylaseprotein and leaf conductance reflect the change in photosynthesisduring the life span of the leaf. (Received November 26, 1983; Accepted February 20, 1984)     

Nocturnal Accumulation of Acid in Leaves of Wall Pennywort (Umbilicus rupestris) Following Exposure to Water Stress

Physiological responses to water stress (drought) have beeninvestigated in Umbilicus rupestris (wall pennywort) by comparingcontrol (well-watered) and draughted plants with respect to(i) diurnal fluctuations in the acid content of the leaves,(ii) CO₂ exchange patterns and (iii) stomatal conductance. Controlplants show no diurnal fluctuations in acid content, whereasafter 6 d of drought a clear CAM-type pattern (nocturnal acidificationfollowed by deacidification in the light) is observed. In controlplants, the CO₂ exchange pattern over a 24 h period is of atypical C-3 ‘square-wave’ type, with extensive CO₂uptake in the light and CO₂ output in the dark. In droughtedplants the day-time CO₂ uptake is confined to a morning ‘burst’,whilst night-time CO₂ output is markedly reduced. There is howeverno net noctural uptake of CO₂. In control plants, stomatal conductanceis high during the day (especially in the first half of theday) falling to a low level at the onset of darkness, and thenrising slowly through the remainder of the night. In droughtedplants, stomatal conductance is very low, except that thereis morning ‘burst’ of high conductance and a periodduring the night when conductance is higher than in controlplants. These results are discussed in relation to the response of U.rupestris to drought both in laboratory and in field conditions. Umbilicus rupestris, wall pennywort, CO₂ exchange, Crassulacean acid metabolism, drought, stomatal conductance, water stress     

Net CO(2) Assimilation Rate of Grapevine Leaves in Response to Trunk Girdling and Gibberellic Acid Application

Net CO₂ assimilation rate (A), stomatal conductance (g_s), and weight per unit leaf area (W) were determined on Thompson Seedless grapevines grown in the field. Treatments included fruit set applications of gibberellic acid (40 milligrams gibberellic acid (GA₃) per liter) to vines, shoots and clusters, alone and in combination with trunk girdling. Leaf A and g_s were measured prior to and 3, 6, and 13 days after fruit set. Weight per unit leaf area was determined on leaves collected subsequent to gas exchange measurements. Leaf A of girdled vines was reduced approximately 30% when compared to the control 13 days after treatment. The reduction in A due to girdling was not as great when vines were sprayed with GA₃. GA₃ sprays alone had no significant effect on A. Stomatal conductance was reduced by girdling 13 days after treatment. Weight per unit leaf area was 17% greater for trunk girdled vines when compared to the controls. Results indicate GA₃ affected net CO₂ assimilation rate only on girdled vines, a treatment which increased weight per unit leaf area.     

Responses of Commelina communis L. Guard Cell Protoplasts to Abscisic Acid

Fitzsimons, P. J. and Weyers, J. D. B. 1987. Responses of Commelinacommunis L. guard cell protoplasts to abscisic acid.—J.exp. Bot. 38: 992–1001. Guard cell protoplasts (GCPs) isolated from the leaf epidermisof Commelina communis L. responded to abscisic acid (ABA) ina manner which was qualitatively and quantitatively similarto that of intact stomata. ABA inhibited swelling of GCPs underlow-CO₂ conditions and swollen GCPs responded to the hormoneby shrinking. Both the absolute volume decrease and the initialrate of shrinking were commensurate with the extent and ratesof solute loss computed for ABA-treated intact, open stomata.This indicates that GCPs represent a suitable experimental systemfor studies of ABA-mediated solute fluxes. A radiotracer equilibrationmethod was developed for the rapid estimation of GCP osmoticvolume changes. Using this technique it was found that, on average,82% of the reduction in solute content caused by ABA treatmentwas due to the loss of K⁺. It is envisaged that electroneutralitymight be maintained during ABA-induced shrinkage of GCPs bynet inward proton movement leading to acidification of the vacuole. Key words: Abscisic acid, Commelina communis L., guard cells, protoplasts     

Apoplastic pH of intact leaves of Vicia faba as influenced by light

The fluorochrome FITC-dextran was used to measure the effectof light on the apoplastic pH of intact Vicia faba leaves withthe ratio imaging technique. In darkadapted leaves the apoplasticpH varied depending on the leaf between 5.2 and 5.9. Red light(660 nm, 4–12 W m^–2) leads to multiphasic responses:in the first seconds an alkalinization ({small tilde}0.3 pHunits), and thereafter an acidification of the leaf apoplast({small tilde}0.4 pH units) were observed. Both effects couldbe inhibited by DCMU. While variation of CO₂ concentration revealedno effect on light-induced apoplastic pH changes, a decreasein O₂ concentration decreased the effect. On the basis of ourdata it is suggested that the influence of photosynthesis onplasmalemma H⁺ ATPase is responsible for the observed effects,rather than altered CO₂ uptake. Key words: Leaf apoplast, apoplastic pH, light, ratio imaging, pH-sensitive fluorescent dye, Vicia fab     

An Association between Flowering and Reduced Stomatal Sensitivity to Water Stress in Pearl Millet [Pennisetum americanum (L.) Leeke]

Stomatal sensitivity to water stress was investigated in pearlmillet [Pennisetum americanum (L.) Leeke] in relation to stageof plant development, leaf water status and ABA content by samplingplants at midday. For the same leaf water potential (), droughtedplants with emerged panicles were found to have a greater leafconductance (g_L), indicative of greater stomatal opening, thanplants sampled prior to panicle emergence. The difference betweensuch flowering (F) and non-flowering (NF) plants in at stomatalclosure was estimated to be at least 0.6 MPa. This differencewas considered unlikely to be the result of differential bulkleaf osmotic adjustment, and for most samples from both F andNF plants, bulk leaf turgor potential (_p) was estimated to bezero. Stomatal closure in NF plants was associated in two genotypes(BJ 104 and line 112) with higher leaf ABA levels. Differencesin ABA levels between F and NF plants were, however, smalleror absent in genotypes Serere 39 and B282. These genotypes wereat lower than BJ 104 and line 112 when sampled and showed smallerdifferences between F and NF plants in conductance. Lower ABA levels in F plants are ascribed either to effectsof leaf ageing or to effects of flowering on ABA content ofthe leaf. Significant differences in g_L in the absence of differencesin ABA content are taken to imply changes in stomatal sensitivityto the hormone or in its access to the stomatal complex. Pennisetum americanum (L.) Leeke, pearl millet, flowering, stomata, water stress, abscisic acid     

Photosynthesis and Diffusion Conductance of the Valencia Orange Fruit under Field Conditions

CO₂ uptake and diffusion conductance of Valencia orange fruits(Citrus sinensis L. Osbeck) were measured in the field duringthe growing season of 1977/78 to ascertain if, as in the leaf,stomata control photosynthesis and transpiration under changingenvironmental conditions. Measurements were made on 15 yearold trees grown in a sandy loam soil and receiving either adry or a wet treatment. Fruit diffusive conductance was measuredwith a modified water vapour diffusion conductance meter andgross photosynthesis was measured with a ¹⁴CO₂ uptake meter.Photosynthetically active radiation (PAR) was measured witha quantum sensor. Fruits exposed to light assimilated CO₂ ata rate which was 25–50% of that assimilated by leaves.The uptake was dependent on fruit size, PAR, chlorophyll content,and on diffusive conductance of the fruit epidermis. Epidermalconductance showed a diurnal trend which was similar in shapeto that of the leaf except in the late afternoon. Cuticularconductance of the fruit was calculated and ranged between 0.22and 0.30 mm s^–1. It was speculated that the CO₂ uptakeby the fruit could support the growth of flavedo cell layerswhen exposed to light. Dry soil caused an increase in the ¹⁴CO₂uptake by fruit possibly caused by the increased potential areaof the stomatal opening per unit of fruit surface area.     

Effects of Prolonged Darkness on the Sensitivity of Leaf Respiration to Carbon Dioxide Concentration in C3and C4Species

Predicting responses of plant and global carbon balance to theincreasing concentration of carbon dioxide in the atmosphererequires an understanding of the response of plant respirationto carbon dioxide concentration ([CO₂]). Direct effects of thecarbon dioxide concentration at which rates of respiration ofplant tissue are measured are quite variable and their effectsremain controversial. One possible source of variation in responsivenessis the energy status of the tissue, which could influence thecontrol coefficients of enzymes, such as cytochrome-c oxidase,whose activity is sensitive to [CO₂]. In this study we comparedresponses of respiration rate to [CO₂] over the range of 60to 1000 µmol mol^-1in fully expanded leaves of four C₃andfour C₄herbaceous species. Responses were measured near themiddle of the normal 10 h dark period, and also after another24 h of darkness. On average, rates of respiration were reducedabout 70% by the prolonged dark period, and leaf dry mass perunit area decreased about 30%. In all species studied, the relativedecrease in respiration rate with increasing [CO₂] was largerafter prolonged darkness. In the C₃species, rates measured at1000 µmol mol^-1CO₂averaged 0.89 of those measured at 60µmol mol^-1in the middle of the normal dark period, and0.70-times when measured after prolonged darkness. In the C₄species,rates measured at 1000 µmol mol^-1CO₂averaged 0.79 of thoseat 60 µmol mol^-1CO₂in the middle of the normal dark period,and 0.51-times when measured after prolonged darkness. In threeof the C₃species and one of the C₄species, the decrease in theabsolute respiration rate between 60 and 1000 µmol mol^-1CO₂wasessentially the same in the middle of the normal night periodand after prolonged darkness. In the other species, the decreasein the absolute rate of respiration with increase in [CO₂] wassubstantially less after prolonged darkness than in the middleof the normal night period. These results indicated that increasingthe [CO₂] at the time of measurement decreased respiration inall species examined, and that this effect was relatively largerin tissues in which the respiration rate was substrate-limited.The larger relative effect of [CO₂] on respiration in tissuesafter prolonged darkness is evidence against a controlling roleof cytochrome-c oxidase in the direct effects of [CO₂] on respiration.Copyright 2001 Annals of Botany Company Carbon dioxide, respiration, Abutilon theophrasti(L.), Amaranthus retroflexus(L.),Amaranthus hypochondriacus (L.), Datura stramonium(L.), Helianthus annuus(L.), Solanum melongena(L.), Sorghum bicolor(L. Moench), Zea mays     

In situ Observations of Stomatal Movements

Kappen, L., Andresen, G. and L?sch, R. 1987. In situ observationsof stomatal movements.—J. exp. Bot. 38: 126–141. A device is described by which stomatal movements in situ canbe observed and recorded continuously in light and in darkness.It is mounted in a conditioned CO₂ exchange measuring chamberso that stomatal movements can be observed whilst CO₂ exchange(photosynthesis and respiration) of the same leaf is measured.Advantages and limitations are discussed. By this method itwas shown that stomata of Vicia faba although responding inthe same direction to environmental stimuli exhibited a widerange of pore widths. Responses to changes of air humidity andof CO₂ content were clearly evident when the leaves were exposedto light. Before stomata closed due to decreasing water vapourpressure differences between leaf and air they showed a markedwidening of the pore. An inverse response occurred when watervapour pressure deficit decreased. In darkness stomata did notrespond to such changes. Key words: Stomata, leaf gas exchange, microscopic observation     

Effects of NORIN 10 and Tom Thumb Dwarfing Genes on Morphology, Physiology and Abscisic Acid Production in Wheat

The pleiotropic effects of three genetically related dwarfinggenes were investigated in near-isogenic lines of wheat. TheNORIN 10 semi-dwarfing alleles, Rht 1 and Rht 2, and the TomThumb allele, Rht 3, were assessed for effects on some vegetativemorphological and physiological characters. The Rht allelesaffected leaf size with a resultant decrease in leaf area ofthe whole plant. Rht 3, which had the most marked effects, reducedleaf area in young plants by as much as 30 per cent. Althoughflag leaf dimensions and stomatal distributions of the flagleaf were altered, the gene had no effect on its area, stomatalconductance or net CO₂ exchange rate. Comparisons of Rht andtall plants revealed no differences in the abscisic acid (ABA)levels of either turgid or partially dehydrated leaves. Triticum aestivum L., wheat, dwarfing genes, leaf structure, abscisic acid, stomatal conductance, CO₂, exchange, relative growth rate     

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     

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.     

The Heritability of Abscisic Acid Accumulation in Water-stressed Leaves of Pearl Millet [Pennisetum americanum (L.) Leeke]

Using detached leaves, two cultivars of pearl millet [Pennisetumamericanum (L.) Leeke], B282 and Serere 39, were assessed forvariation in the capacity to accumulate ABA in response to waterstress. Significant differences in ABA accumulation were detectedbetween cultivars and between different inbred lines withina cultivar, but within lines there was much less variation inthis character. In crosses between individual lines of B282(low ABA) and Serere 39 (high ABA), ABA accumulation in theF₁ was mid-way between parental values, indicating additivegenetic control and lack of dominance. Selfed progeny of a B282 x Serere 39 cross were selected forcontrasting ABA accumulation in the F₂ to F₄ generations. Asixfold range in ABA accumulation was found amongst 207 F₂ progeny.This increased to nearly ninefold at F₃ and F₄. Regression analysisindicated high heritability of ABA accumulation and rapid approachto homozygosity. As the cross studied involved a dwarf (B282) and a tall (Serere39) parent, segregation occurred for height as well as for ABA,though not entirely independently. Tall F₃ progeny had significantlyhigher ABA contents than dwarf progeny and high ABA was thereforeassociated with other traits (e.g. large leaves, high leaf percent d. wt) characteristic of tall plants. Nevertheless, therewas a substantial range of ABA content within both groups whichwas uncorrelated with height and other characters. The potential use of the selections in studies on drought responseis briefly discussed. Pennisetum americanum (L.), Leeke, pearl millet, abscisic acid accumulation, water stress, genetic differences, inheritance