Release of Guttation Fluid from Passive Hydathodes of Intact Barley Plants. II. The Effects of Abscisic Acid and Cytokinins

Guttation was used as a non-destructive way to study the flowof water and mineral ions from the roots and compared with parallelmeasurements of root exudation. Guttation of the leaves of barley seedlings depends on age andon the culture solution. Best rates of guttation were obtainedwith the primary leaves of 6- to 7-day-old seedlings grown onfull mineral nutrient solution. The growing leaf tissue becomessaturated with K⁺ below 1.5 mM K⁺ in the medium, whereas K⁺concentration in the guttated fluid still increases furtheras K⁺ concentration in the medium is raised. At 3 mM K⁺ averagevalues of guttation were 1.4–2.4 mm³ h^–1 per plantwith a K⁺ concentration of 10–20 mM; for exuding plantsthe flow was 4.2–7.6 mm³ h^–1 per plant and K⁺ concentration35–55 mM. Abscisic acid (ABA) at 10^–6 to 10^–4 M 0–2h after addition to the root medium increased volume flow ofguttation and exudation and the amount of K⁺ exported. Threeh after addition of ABA both volume and amount of K⁺ were reduced.There was an ABA-dependent increase in water permeability (Lp)of exuding roots shortly after ABA addition. Later Lp was decreasedby 35 per cent and salt export by 60 per cent suggesting aneffect of ABA on salt transport to the xylem apart from itseffect on Lp. Benzyladenine (5 x 10^–8 to 10^–5 M)and kinetin (5 x 10^–6 M) progressively reduced volumeflow and K⁺ export in guttation and exudation and reduced Lp. Guttation showed a qualitatively similar response to phytohormonesas found here and elsewhere using exuding roots. Hordeum vulgare L., barley, guttation, abscisic acid, cytokinins, benzyl adenine, kinetin     

Bl?tenbildung bei Lemna paucicostata 6746 durch kombinierte Anwendung von Abscisins?ure und GCG

To a certain extent the flowering of Lemna paucicostata 6746is evoked in continuous light by application of abscisic acid(ABA) and CCC. Moreover, the action of the combined substancesappears in two separate concentration ranges. In the range ofABA 2?10^–9 M/CCC 10^–7–10^–6 M floweringis initiated without inhibition of vegetative growth and proceedsonly in the presence of high intensity light and sucrose. Acombination of ABA 2?10^–5 M/CCC 10^–3M simultaneouslycauses a strong inhibition of frond multiplication. Here theeffect can be observed also under low intensity light conditionsand without sucrose in the medium. A range with flower inhibitingactivity lies between the two flower promoting concentrationranges. (Received November 16, 1972; )     

Photoperiodically Induced Changes in Seed Growth Rate of Soybean as Related to Endogenous Concentrations of ABA and Sucrose in Seed Tissues

Short-day photoperiods can increase the partitioning of assimilatesto filling seeds of soybean (Glycine max L. Merr.), resultingin higher seed growth rates. The plant growth substance ABAhas been implicated in the regulation of assimilate transferwithin filling soybean seeds. Thus, we hypothesized that anincreased concentration of endogenous ABA in seeds may enhancesucrose accumulation and seed growth rate of soybeans exposedto short-day photoperiods. Plants of cv. Hood 75 were grownin a greenhouse under an 8-h short-day photoperiod (SD) until11 d after anthesis (DAA) of the first flower, when half ofthe plants were transferred to a night-interruption (NI) treatment(3 h of low-intensity light inserted into the middle of thedark period). Plants remaining in SD throughout seed developmenthad seed growth rates 43% higher than that of plants shiftedto NI (7·6 mg seed^–1 d^–1 vs. 5·3 mgseed^–1 d^–1). On a tissue-water basis, the concentrationof ABA in SD seeds increased rapidly from 7.6 µmol l^–1at 11 DAA to 65·2 µmol l^–1 at 18 DAA, butthen declined to 6·6 µmol l^–1 by 39 DAA.In contrast, the concentration of ABA increased more slowlyin NI seeds, reaching only 47·4 µmol l^–1by 18 DAA, peaking at 57·0 µmol l^–1 on 25DAA, and declining to 10·2 µmol l^–1 by 39DAA. The concentration of sucrose in SD embryos peaked at 73·5mmol l^–1 on 25 DAA and remained relatively constant forthe remainder of the seed-filling period. In NI, the concentrationof sucrose reached only 38·3 mmol 1^–1 by 25 DAA,and peaked at 61·5 µmol l^–1 on 32 DAA. Thusin both SD and NI, sucrose accumulated in embryos only afterthe peak in ABA concentration, suggesting that ABA may havestimulated sucrose movement to the seeds. The earlier accumulationof ABA and sucrose in SD suggests that ABA may have increasedassimilate availability during the critical cell-division period,thus regulating cotyledon cell number and subsequent seed growthrate for the remainder of the seed-filling period. Glycine max L. Merr. cv. Hood 75, soybean, assimilate partitioning, abscisic acid, photoperiod, source-sink     

Developmental Responses to Drought and Abscisic Acid in Sunflower Roots: 2. MITOTIC ACTIVITY

Mitotic activity was studied in the root apices of aeroponicallygrown sunflower seedlings (Helianthus annum L. var. RussianGiant) which were draughted or treated with abscisic acid (ABA)over a 7 d period. Labelling index (LI) and mitotic index (MI)were scored from autoradiographs of median longitudinal sectionsof [³H] methyl-thymidine treated root apices. Both drought stressand ABA-treatment (at a concentration of 10^–2 mol m^–3inhibited DNA synthesis and mitosis within the first 6 h oftreatment. The depression of mitotic activity was first evidentin the proximal regions of the meristem (1000–1500 µmfrom the cap junction). This was followed by a general depressionof mitotic activity throughout the meristem which was, in turn,followed by a partial recovery of mitotic activity in the distalregions of the meristem. The beginning of this partial recoverywas concurrent with the activation of the quiescent centre (QC).Treatment with lower concentrations of ABA (10^–3 mol m^–3and 10^–4 mol m^–3) also inhibited mitotic activity.Exogenous supplements of sucrose to the plant did not alleviatethe inhibition of mitotic activity by drought or ABA. Thesefindings support the hypothesis that ABA mediates drought-inducedchanges in the primary development of sunflower roots. Key words: Abscisic acid, drought, mitotic activity     

Exogenous ABA as a Modulator of the Response of Sorghum to High Salinity

Treatment of Sorghum bicolor (L.) Moench, cv. 610, with abscisicacid (ABA) during the first week of sahnization with 150 molm^–3 NaCl induced enhancement of growth and acceleratedadaptation to high salinity (300 mol m^–3 NaCl) Adaptationis defined as the development of the ability of the plant tosurvive, grow, and set seeds upon exposure to a NaCl concentrationwhich is lethal for the unadapted plant In the absence of ABAthe saline pretreatment requires 20 d for the development ofadaptation (Amzallag et al., 1990), with ABA treatment the sameresult is achieved within approximately one week The exposureof the plants to non-lethal salinity (150 mol m^–3 NaCl)apparently triggers a transient sensitivity to ABA lasting forabout 8 to 10 d following the beginning of sahnization Thisperiod coincides with an increase in leaf PEP carboxylase activitywhich seems to occur faster if the plants are treated with ABA.Exogenous ABA-induced enhancement of growth and control of shootNa⁺ concentration, occur at a lower ABA concentration (10 mmolm^–3) than the induction of adaptation to salinity whichoc curs at 40 mmol m^–3 or above. The lowered shoot Na⁺concentration which is induced by a low ABA concentration isnot sufficient to induce survival of the plants in high salinity(300 mol m^–3 NaCl). Key words: Growth, adaptation to salinity, ABA     

Changes in Stomatal Conductance in Intact Ageing Wheat Leaves in Response to Abscisic Acid

The characteristics of ABA-induced changes in the fluxes ofCO₂ and water vapour from whole leaves of spring wheat (Triticumaestivum cv. Wembley) were examined. Aqueous solutions of ABAwere supplied via the transpiration stream to intact leavesof different ages mounted within a gas exchange cuvette. ABA caused a reduction in stomatal conductance (g) that wasproportional to the concentration in the solution fed to theleaf. For the maintenance of a reduction in g there was a requirementfor a continual supply of ABA. At concentrations greater than10^–2 mol m^–3 ABA reduced g by at least 50% of thecontrol value, while 1.0 mol m^–3 closed stomata within2 h. Concentrations as low as 10^–3 mol m^–3 produceda 20% reduction in g. As leaves aged they became less responsiveto applied ABA. The possibility that the stomatal response may change aftera leaf has previously experienced a pulse of ABA was exploredby repeating the exposure of a leaf to 10^–2 mol m^–3ABA. The first pulse of ABA produced a greater reduction ing than a subsequent exposure the following day. This declinein response of g to ABA on repeated exposure was maintainedwith leaves of different ages. The characteristics of the stomatal response to ABA are discussedin the context of what is known about the location of receptorsfor the hormone. It seems likely that a failure to respond toABA that has previously accumulated in the guard cells shouldbe viewed by means of maximizing the sensitivity to the currentsupply of ABA. It is suggested that the smaller response ofthe stomata of older leaves to ABA makes them more susceptibleto water stress, so that they can act as sensors for decliningwater potentials to give early protection to younger, metabolicallyactive leaves. Key words: Abscisic acid, leaf age, stomatal conductance, Triticum aestivum     

The Effects of Cytokinins and ABA on Stomatal Behaviour of Maize and Commelina

Epidermal strips and leaf fragments of Commelina and leaf fragmentsof maize were incubated on solutions containing naturally-occurringor synthetic cytokinins and/or ABA. The effects of these treatmentson stomatal behaviour were assessed. Cytokinins alone did notpromote stomatal opening in either species but concentrationsof both zeatin and kinetin from 10^–3 to 10^–1 molm^–3 caused some reversal of ABA-stimulated closure ofmaize stomata. The reversal of the ABA effect increased withincreasing cytokinin concentration. Cytokinins had no effecton ABA-stimulated closure of Commelina stomata. When appliedalone, at high concentration (10^–1 mol m^–3), toCommelina epidermis or leaf pieces both zeatin and kinetin restrictedstomatal opening. Key words: ABA, Cytokinins, Stomata, Maize, Commelina     

Effect of abscisic acid on elongation and kinetin-induced tuberization of isolated stolons of Solarium tuberosum L.

The response of isolated stolons cultured in vitro, to abscisicacid (ABA) has been studied in the presence and absence of kinetin(6-furfurylaminopurine). ABA alone in concentrations from 7.5x 10^–4 mM to 7.5 x 10^–2 mM, inhibited stolon elongationbut failed to promote tuber initiation. In the presence of kinetin,ABA at concentrations of 3.0 x 10^–2 and 7.5 x 10^–2mM markedly inhibited kinetin-induced tuber initiation and stolonelongation, but at 7.5 x 10^–4 and 7.5 x 10^–3 mMABA did not prevent tuber initiation. When stolons were incubated on a medium containing kinetin andlater transferred to one containing ABA with or without kinetin,the inhibitory effect of ABA decreased appreciably as the timeof incubation on kinetin is increased. The results are discussed in relation to the role of ABA inthe inhibition of nucleic acid and protein synthesis and theinteraction with cytokinins and the possible effect of ABA onkinetin uptake, transport and accumulation at the locus of action. (Received February 26, 1969; )     

The Effects of Partially Drying Part of the Root System of Helianthus annuus on the Abscisic Acid Content of the Roots, Xylem Sap and Leaves

Plants of Helianthus annuus were grown in soil in pots suchthat approximately 30% of the root system protruded throughthe base of the pot. After 7 d further growth in aerated nutrientsolution, the attached, protruding roots were air-dried for10–15 min and thereafter surrounded with moist still air,in the dark, for 49 h, whilst the soil was kept at field capacity.The roots of the control plants remained in the nutrient solutionthroughout the experiment. This treatment rapidly reduced the water content of protrudingroots from 20.5 to 17.8 g g^–1 dry mass (DM), which remainedless than that of the control roots for the rest of the experiment.This treatment also reduced root turgor and water potential.The abscisic acid (ABA) concentrations in the protruding roots,xylem sap and leaves of the treated plants increased significantly,compared to values recorded for control plants. In treated roots, the ABA concentration was significantly increased4 h after treatment, with a maximum of 4.4+0.1 nmol g^–1(DM) after 25 h. The ABA concentration in the xylem sap of thetreated plants was significantly greater than in the controls25 h, 30 h, and 49 h after the partial drying of the roots,with a maximum concentration of approximately 970 pmol ABA cm-3at 49 h. Initially, the ABA concentration in the leaves was0.45 nmol g^–1 (DM) which increased significantly to 1.1±0.1 nmol g^–1 at 25 h, to 1.7±0.3 nmol g^–1at 49 h. Leaf conductance was significantly less in plants with air-driedroots than in the controls 8 h after the start of the treatmentand thereafter. The water relations of the leaves of the treatedplants did not differ from those of the control plants. These results confirm previous reports that ABA is rapidly generatedin partially-dried and attached root systems and demonstratesa concomitant large increase in the ABA content of the xylemsap. It is suggested that partial dehydration of some of theroots of Helianthus annuus, increases ABA concentration in thetranspiration stream and decreases leaf conductance in the absenceof changes in leaf water status. As these responses were initiatedin free-growing roots the stimulus is independent of any increasesin soil shear strength that are associated with soil drying. Key words: Soil drying, roots, ABA, leaf conductance, water relations     

Hormonal responses to partial drying of the root system of Helianthus annuus

Plants of Helianthus annuus were pot-grown in soil, with approximately30% of the root system protruding through the base. After 7d, the upper part of the root system of half of the plants wasexposed to drought (internal roots) while the lower part waskept in aerated nutrient solution (protruding root). The treatmentrapidly reduced the internal roots' water content from 26.1to 21.9 g g^–1 dry weight (DW), while in protruding rootsof stressed plants it slowly and continuously decreased from31.9 to 25.2 g g^–1 DW. Leaf water content rapidly decreasedin treated plants from 7.4 to 6.4 g g^–1 DW in the first2d and then reached a plateau. In stressed plants leaf stomatalresistance was significantly higher in the first 3 d while leafwater potential was lower only on the last day. Abscisic acid (ABA) concentration in treated plants increasedsignificantly compared to the controls. In treated internalroots, ABA rose from the first day, reaching a maximum of 1.48±0.49nmol g^–1 DW after 3 d. In treated protruding roots a maximumof 0.99±0.09 nmol g^–1 DW was reached after 1 d.ABA concentration in the xylem sap increased 2 d and 3 d afterthe start of soil drying, with a maximum of 113±12nmoll^–1 during the third day. The ABA rise in the leaves oftreated plants was less significant. Indol-3yl-acetic acid (IAA) concentration in internal rootsof treated plants reached a maximum of 22.54±3.34 nmolg^–1 DW on the third day, then decreased dramatically.The protruding root system of control plants showed a maximumvalue of 16.05±1.77 nmol g^–1 DW on the sixth day. Little difference in cytokinin content of xylem sap was notedbetween control and treated plants. Hormonal variations in different parts of the plant are discussedin relation to drought stress. Key words: Soil drying, roots, ABA, IAA, cytokinins     

Stomatal Responses to Applied ABA and CO2 in Epidermis Detached from Well-Watered and Water-Stressed Plants of Commelina communis L.

Epidermal strips from either well-watered or water-stressedplants of Commelina communis L. were subjected to a range ofABA concentrations (10^–6–10^–3 mol m^–3)in the presence (330 parts 10^–6 in air) or virtual absence(3 parts 10–6 in air) of CO₂. The stomatal response toCO₂ was greater in epidermis from water-stressed plants, althoughthere was a distinct CO₂ response in epidermis from well-wateredplants. Additions of ABA via the incubation medium had littleeffect on the relative CO₂ response. Stomata responded to ABAboth in the presence and virtual absence of CO₂, but the relativeresponse to ABA was greatest in the high CO₂ treatment. Whenwell-watered plants were sprayed with a 10^–1 mol m^–3ABA solution 1 d prior to use, the stomatal response of detachedepidermis to both CO₂ and ABA was very similar to that of epidermisdetached from water-stressed leaves. It is hypothesized thata prolonged exposure to ABA is necessary before there is anymodification of the CO₂ response of stomata.     

Carrier-Mediated ABA Uptake by Suspension-Cultured Phaseolus coccineus L. Cells: Stereospecificity and Inhibition by Ionones and ABA Esters

Astle, M. and Rubery, P. 1987. Carrier-mediated ABA uptake bysuspension-cultured Phaseolus coccineus L. cells: Stereospecificityand inhibition by ionones and ABA esters.—J. exp. Bot.38: 150–163. The substrate for the abscisic acid (ABA) carrier in Phaseoluscoccineus L. suspension-cultured cells is shown to be the (S)ABAenantiomer, K_m = 1?0 mmol m^–3. The methyl (MeABA) andphenyl (PheABA) esters of ABA inhibit carrier-mediated uptakeof ABA with half-maximal inhibition achieved at about 7?0 mmolm^–3 and 10 mmol m^–3 respectively: with (S)MeABAthis value is decreased to about 2?0 mmol m^–3. There isno demethylation of radioactive MeABA by the cells during 5min incubations. Although MeABA reversibly inhibits the ABAcarrier, it is not a transport substrate: association of radioactiveMeABA with living cells is unaffected by non-radioactive MeABAor ABA and, by comparison with frozen-and-thawed cells, it isshown that the radioactivity remains extracellular. It is proposedthat MeABA binds to the carrier to form an abortive complexthat is not translocated. The terpenoid ABA analogue LAB 144143also inhibits carrier-mediated ABA uptake. At concentrationsup to about 20 mmol m^–3 - and ß-ionone specificallyinhibit the ABA carrier with the half-maximal effect at about0?6 mmol m^–3 ß-ionone. However, at higher iononeconcentrations, the uptake of ABA, indol-3-yl acetic acid andof 5,5-dimethyloxazolidine-2,4-dione (DMO) are all stimulated:this may reflect general permeabilization of the membrane toweak acids by ionone. Key words: Uptake carrier, abscisic acid, methyl and phenyl esters of ABA, ionone, Phaseolus coccineus L. suspension culture     

Normalizing Development of Cultured Triticum aestivum L. Embryos: I. LOW OXYGEN TENSIONS AND EXOGENOUS ABA

Wheat (Triticum aestivum L.) embryos form in dynamically-regulatedovular environments. Our objectives were to improve developmentof cultured immature wheat embryos by simulating, in vitro,abscisic acid (ABA) levels and O₂ tensions as found in wheatovules during zygotic embryogenesis. We characterized from intactwheat kernels embryo respiration, embryo morphology and embryoand endosperm + ABA levels at 13, 19 and 25 d post-anthesis(DPA). Young (13 DPA) embryos were then excised and culturedin vitro, where they were exposed to 0·2 or 2·Ommol m^–3 ±ABA and 2.·1, 2·5 or 7·4mol m^–3 (6, 7 and 21%, respectively) gaseous O₂. At 6and 12 d in culture, + ABA levels, embryo respiration and embryomorphology were characterized by treatment. Thirteen-day-oldembryos from two different plant populations differed by 17-foldin initial ABA content. However, this difference did not affectprecocious germination in vitro, nor did it affect the amountof exogenous ABA required to reduce precocious germination by40%. In this respect, embryos from both populations were equallysensitive to exogenous ABA. Cavity sap O₂ levels (2·1to 2·5 mol m^–3) were much more effective in preventingprecocious germination of cultured embryos than were cavitysap levels of ABA (0·2 to 2·0 mmol m^–3).The combination of physiological levels of both ABA and O₂ largelynormalized DW accumulation and embryo morphology without alteringendogenous + ABA levels. Residual respiration of cultured embryoswas higher than that of embryos grown in situ, and was not influencedby the exogenous O₂ and ABA treatments Key words: Abscisic acid, embryo development, oxygen tensions, respiration, wheat     

Inhibition of Light-Stimulated Leaf Expansion by Abscisic Acid

Abscisic acid (ABA) applied to intact bean (Phaseolus vulgaris)leaves or to isolated leaf discs inhibits light-stimulated cellenlargement This effect may be obtained with 10^–4 molm^–3 ABA, but is more significant at higher concentrations.The inhibition of disc expansion by ABA is greater for discsprovided with an external supply of sucrose than for discs providedwith KC1, and may be completely overcome by increasing the KC1concentration externally to 50 mol m^–3. Decreased growthrate of ABA-treated tissue is not correlated with loss of solutesfrom growing cells, but is correlated with a decrease in cellwall extensibility. ABA does not prevent light-stimulated acidificationof the leaf surface, and stimulates the acidification of theexternal solution by leaf pieces. However, the capacity of thecell walls to undergo acid-induced wall loosening is diminishedby ABA-treatment. The possibility that ABA acts directly byinhibiting growth processes at the cellular level, or indirectlyby causing stomatal closure, is discussed. Key words: Phaseolus vulgaris, ABA, Inhibition, Leaf expansion     

Abscisic Acid and Apical Dominance in Phaseolus coccineus L. The Role of Tissue Age

Abscisic acid (ABA) applied to the decapitated second internodeof runner bean plants enhanced outgrowth of lateral buds onlywhen internode stumps were no longer elongating. Applied toelongating internodes of slightly younger plants, ABA causesinhibition of bud outgrowth. Together with 10^–4 M indol-3-ylacetic acid (IAA), ABA stimulated internode elongation and interactedadditively in the inhibition of bud outgrowth. A mixture of10^–5 M ABA and 10^–6 M gibberellic acid (GA₃ ) causedsimilar effects on internode growth as IAA + ABA, but was mutuallyantagonistic in effect on growth of the lateral buds. Abscisic acid, apical dominance, gibberellic acid, indol-3yl acetic acid, Phaseolus coccineus, bean     

Effect of abscisic acid on differentiation and ribulose diphosphate carboxylase of chloroplasts

Daucus carota tissues were grown on Murashige-Skoog medium (MS)at different concentrations with abscisic acid (ABA). Sevenbands of chloroplast fractions were obtained on a sucrose gradient.At 10^–5M, ABA highly increased chlorophyll and proteinnitrogen content of medium density chloroplasts. With increasingage of the tissues, the most active chloroplasts according totheir ¹⁴CO₂ fixation were found in smaller numbers. When treatedwith 10^–5 M ABA, 34 day-old tissues cultivated in vitroshowed the chloroplast pattern of 110 day-old tissues. The effectof ABA—given to the tissues during a short pretreatmentor continuously present in the culture medium—on the ribulosediphosphate carboxylase activity was analysed. It was foundthat ABA at 10^–5 M strongly inhibited ¹⁴CO₂ fixation. (Received December 20, 1977; )     

Ineffectiveness of Abscisic Acid in Stomatal Closure of Yellow Lupin, Lupinus luteus var. Weiko III

Stomata of yellow lupin leaves are remarkably insensitive toabscisic acid (ABA). Stomatal resistance was monitored usingboth a viscous now porometer and a diffusion porometer. Resultswere confirmed with scanning electron microscopy. When exogenousABA solutions were supplied via petioles, 10^–6 M solutionshad no effect on stomatal resistance. Upper (adaxial) stomatawere not affected by 10^–5 M ABA but lower stomata showed3-fold more resistance after 2 h. Stomata of both surfaces closedafter 30 min in 10^–4 M ABA. Isolated epidermal peels of lupin leaves were floated on ABAsolutions yet upper surface peels showed no stomatal closingin 10^–4 M ABA, while lower surface stomata closed to abarely significant extent. Stomata of intact leaves were not very sensitive to darkness,showing at most a doubling in resistance after 6 h darkness.Complete stomatal closure, however, was readily produced bywilting leaves. Hence, lupin stomata are physically capableof closing. Endogenous ABA levels of water-stressed leaves increased approximately10-fold, which corresponds to concentrations below 10 µMABA. It is concluded that ABA is unlikely to play a role incontrolling short-term stomatal response of lupins.     

Microelectrophoretic and 9-Aminoacridine Fluorescence Study of the Surface Electrical Properties of Suspension Cultured Catharanthus roseus Cells and Isolated Protoplasts: Effects of Abscisic Acid Treatment

The effects of abscisic acid (ABA) treatments on the surfaceelectrical properties of cells and isolated protoplasts fromCatharanthus roseus cell suspension cultures were studied byelectrophoretic mobility and 9-aminoacridine (9AA) fluorescencemeasurements. The surface charge densities of the cells andprotoplasts estimated from electrokinetic data were –0.064Cm^–2and –0.048 C m^–2 respectively. These values wereclose to that estimated by 9AA fluorescence technique i.e.,–0.053 Cm^–2 for the cells and –0.041 Cm^–2for the isolated protoplasts accordingly. The net negative surfacecharge density decreased after application of 10 µM and50 µM ABA in both cells and protoplats, the more pronouncedeffect being observed at 10 µM ABA. When 100 µMABA was supplemented to the cell suspension culture the oppositeeffect was observed. The average charge density increased to–0.074 C m^–2 for the cells, and to –0.055C m^–2 for protoplasts, as revealed from the 9AA measurements.The results are discussed in terms of specific concentrationdependent ABA-induced alterations of the electrostatic propertiesof cell and protoplast membranes. (Received December 12, 1994; Accepted April 3, 1995)     

Changes in the Translatable RNA Population during Abscisic Acid Induce Freezing Tolerance in Bromegrass Suspension Culture

Abscisic acid (ABA) has been shown to increase freezing toleranceof bromegrass (Bromus in-ermis Leyss cv. Manchar) cell suspensioncultures from a LT₅₀ (the temperature at which 50% cells werekilled) of –7 to – 30?C in 5 days at 23?C. Our objectivewas to study the qualitative changes in the translatable RNApopulation during ABA induced frost tolernace. In vitro translationproducts of poly(A)⁺ RNA isolated from bromegrass cells withor without 75 µM ABA treatment for various periods oftime were separated by 2D-PAGE and visualized by fluorography.SDS soluble proteins from the same treatments were also separatedby 20-PAGE. After 5 days treatment, at least 22 new or increasedabundance SDS soluble polypeptides were observed. From fluorographs,29 novel or increased abundance in vitro translation productscould be detected. The pattern of changes between ABA inducedSDS-soluble proteins and translation products from the 2D gelswere similar. A time course study (0–7 days) showed that17 of the 29 translation products were detected after 1 dayABA treatment, and at least 14 were present after 1 h. Coldtreatment (+4?C) induced fewer changes in the pool of translatableRNA than with ABA treatment. Three translation products inducedby cold appear to be similar to 3 of the ABA induced translationproducts. The majority of the ABA inducible translatable RNAsappeared at 10 µM or higher which coincides with the inductionof freezing tolerance. Many of these ABA inducible RNAs persisted7 days after ABA was removed from the media and correspondinglythe LT₅₀ (–17?C) was still well above the control level(–17?C). The results suggest that ABA alters the poolof translatable RNAs during induction of freezing tolerancein bromegrass suspension culture cells. ¹Oregon Agricultural Experiment Station Technical Paper No.9256. (Received August 3, 1990; Accepted October 18, 1990)     

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.