Increase In Abscisic Acid Content Research Articles

A physiologically-induced resistance of Phaseolus vulgaris to a compatible race of Colletotrichum lindemuthianum is associated with increases in ABA content

Isolated hypocotyls from Phaseolus vulgaris seedlings to which different organs were left attached differed in their resistance to a compatible race of the fungal pathogen Colletotrichum lindemuthianum. Hypocotyls which retained cotyledons or leaves were more resistant than those which lacked these organs. The degree of resistance, assessed 10 days after inoculation, was related to the concentration of abscisic acid (ABA) in hypocotyls 4 days after inoculation, when the pathogen was in its progressive biotrophic phase. Symptom severity decreased following application of ABA to susceptible hypocotyls. Application of fluridone, an inhibitor of ABA biosynthesis, to resistant hypocotyls increased symptom severity. ABA had no direct effect on pathogen growth. The results suggest that the resistance induced by retention of leaves and/or cotyledons results from ABA-induced changes in host cell physiology leading to a reduction in the extent of the pathogen's biotrophic growth.

Abscisic Acid Levels during Early Seed Development in Sechium edule Sw

The time-course growth of single tissues in pollinated and unpollinated ovules of Sechium edule Sw. is described in relation to the endogenous levels of abscisic acid. Quantitation of abscisic acid (ABA) in the minute amounts of material obtained after ovule dissection has been performed by using a highly specific and sensitive solid-phase radioimmunoassay based on a monoclonal antibody raised against free (S)-ABA. While the absolute amount of ABA rises in both types of ovules, only in unpollinated ones does this leads to an increase in the hormone concentration. Infact in pollinated ovules the rapid growth following pollination prevents, through a dilution effect, the increase in ABA concentration. Growth patterns and endogenous ABA levels are similar for integuments and nucellus tissues either in pollinated or unpollinated ovules. It is suggested that the growth inhibition induced by the increase in ABA concentration after anthesis could be counteracted by the pollination triggered fast ovule growth.

Stress-Induced Accumulation of Wheat Germ Agglutinin and Abscisic Acid in Roots of Wheat Seedlings

Wheat germ agglutinin (WGA) levels in roots of 2-day-old wheat seedlings increased up to three-fold when stressed by air-drying. Similar results were obtained when seedling roots were incubated either in 0.5 molar mannitol or 180 grams per liter polyethylene glycol 6000, with a peak level of WGA after 5 hours of stress. Longer periods of osmotic treatment resulted in a gradual decline of WGA in the roots. Since excised wheat roots incorporate more [(35)S]cysteine into WGA under stress conditions, the observed increase of lectin levels is due to de novo synthesis. Measurement of abscisic acid (ABA) levels in roots of control and stressed seedlings indicated a 10-fold increase upon air-drying. Similarly, a five- and seven-fold increase of ABA content of seedling roots was found after 2 hours of osmotic stress by polyethylene glycol 6000 and mannitol, respectively. Finally, the stress-induced increase of WGA in wheat roots could be inhibited by growing seedlings in the presence of fluridone, an inhibitor of ABA synthesis. These results indicate that roots of water-stressed wheat seedlings (a) contain more WGA as a result of an increased de novo synthesis of this lectin, and (b) exhibit higher ABA levels. The stress-induced increase of lectin accumulation seems to be under control of ABA.

Abscisic Acid Content of Algae under Stress*

AbstractThe distribution of the phytohormone, abscisic acid (ABA), within the phylum of Phycophyta was investigated by an enzyme‐linked immunoassay (ELISA). Of 64 algal species tested (originating from 9 divisions, 20 classes and 36 orders, including procaryotes) all species contained ABA, whereas no ABA could be detected in the bacteria Escherichia coli, Rhodospirillum rubrum, and Halobacterium halobium. It is concluded that ABA is universally distributed within the algal kingdom and is not restricted to cormophytes. The ability to synthesize ABA must have been developed even within the procaryotes. The physiological role of ABA in some selected algae was studied by investigating 1. the distribution of ABA between the cells and the culture medium, 2. the responses of endogenous ABA to stress, 3. the synthesis of 14C‐ABA from externally applied 14C‐mevalonic acid, 4. the metabolism of ABA, 5. the effect of externally applied ABA on various physiological reactions of the algae, and the effect of norflurazon on ABA content. 14C‐mevalonic acid served as precursor of 14C‐ABA synthesis in Dunaliella cells and ABA was metabolised to the same products which have been observed in higher plants. In D. parva the internal ABA level increased upon hyperosmotic salt shocks, and in D. acidophila upon alkalization of the medium. Norflurazon caused an increase of ABA content in Dunaliella. Externally applied ABA did not affect photosynthesis, respiration and K+ content of the cells. The permeability of the plasma membrane of D. acidophila to water was slightly decreased by ABA. The possible physiological function of ABA in algae is discussed.

Determination of endogenous abscisic acid levels in immature cereal embryos during in vitro culture

Levels of endogenous abscisic acid (ABA) in immature wheat (Triticum aestivum cv. Timmo) and barley (Hordeum vulgare cv. Golden Promise) embryos have been determined by enzyme-linked immunosorbent assay. Embryos of both cereal species showed an increase in ABA content during development on the parent plant. Immature embryos were excised and cultured in vitro on nutrient media that led to precocious germination or on media containing 9% (w/v) mannitol that maintained their developmental arrest. Barley and wheat embryos responded to these culture conditions in an identical manner with respect to changes in morphology, fresh weight, protein and lectin content. However, in complete contrast, the ABA content of barley embryos increased by an order of magnitude during culture on mannitol, whereas that of wheat embryos showed no significant change. The results are discussed within the context of the role of ABA in the regulation of embryo development.

Are Roots a Source of Abscisic Acid for the Shoots of Flooded Pea Plants?

Jackson, M. B., Young, S. F. and Hall, K. C. 1988. Are roots a source of abscisic acid for the shoots of flooded pea plants?—J. exp. Bot. 39: 1631-1637. Flooding the soil for 2-5 d decreased stomatal conductances of pea plants (Pisum sativum L., cv. Sprite) with six or seven leaves. This coincided with slower transpiration, increased leaf water potentials and increased concentrations of abscisic acid (ABA) in the leaves. No increase in ABA was found in the terminal 20 mm of roots of flooded plants over the same time period. Small stomatal conductances associated with increases in foliar ABA were also found in plants grown in nutrient solution when aeration was halted, causing the equilibrium partial pressures of dissolved oxygen to fall below 0-5 kPa. No increase in ABA concentration in young secondary roots of the non-aerated plants was detected after 24, 48 or 72 h, even when the shoot, the presumed site of deposition for any ABA from the roots, was removed 5-6 h before analysis. Similarly, ABA concentrations in roots were not increased when the nutrient solution was de-oxygenated by continuous purging with nitrogen gas. The abscisic acid concentration in leaf epidermis, the tissue most likely to be the recipient of any ABA moving in the transpiration stream from oxygen-deficient roots, was lower than in the remaining parts of the leaf when examined in the mutant Argenteum which possesses easily removable epidermal layers. It is concluded that the leaves of plants subjected to flooding of the soil or oxygen shortage in the root environment are not enriched substantially with ABA from the roots. A more probable source of this growth regulator is the leaf itself.

Effect of thidiazuron on abscisic acid content in apple bud relative to dormancy

The effect of N‐phenyl‐N′‐1,2,3,‐thidiazol‐5‐ylurea (thidiazuron, Dropp, SN 49537) on abscisic acid (ABA) level in apple (Malus domestica Borkh. cv. York Imperial) buds associated with bud break and bud development was determined. The data showed that increased ABA content in apple buds was associated with thidiazuron‐induced bud break and bud development. ABA stimulated growth of apple buds that had emerged from dormancy by thidiazuron treatment. The ABA in apple buds was confirmed by GC‐EIMS and GC‐CIMS.

Early stomatal closure in waterlogged pea plants is mediated by abscisic acid in the absence of foliar water deficits

Abstract Soil waterlogging decreased leaf conductance (interpreted as stomatal closure) of vegetative pea plants (Pisuin sativum L. cv. ‘Sprite’) approximately 24 h after the start of flooding, i.e. from the beginning of the second 16 h‐long photo‐period. Both adaxial and abaxial surfaces of leaves of various ages and the stipules were affected. Stomatal closure was sustained for at least 3 d with no decrease in foliar hydration measured as water content per unit area, leaf water potential or leaf water saturation deficit. Instead, leaves became increasingly hydrated in association with slower transpiration. These changes in the waterlogged plants over 3 d were accompanied by up to 10‐fold increases in the concentration of endogenous abscisic acid (ABA). Waterlogging also increased foliar hydration and ABA concentrations in the dark.Leaves detached from non‐waterlogged plants and maintained in vials of water for up to 3 d behaved in a similar way to leaves on flooded plants, i.e. stomata closed in the absence of a water deficit but in association with increased ABA content. Applying ABA through the transpiration stream to freshly detached leaflets partially closed stomata within 15 min. The extractable concentrations of ABA associated with this closure were similar to those found in flooded plants. When an ABA‐deficient ‘wilty’ mutant of pea was waterlogged, the extent of stomatal closure was less pronounced than that in ordinary non‐mutant plants, and the associated increase in foliar ABA was correspondingly smaller. Similarly, waterlogging closed stomata of tomato plants within 24 h, but no such closure was seen in ‘flacca’, a corresponding ABA‐deficient mutant.The results provide an example of stomatal closure brought about by stress in the root environment in the absence of water deficiency. The correlative factor operating between the roots and shoots appeared to be an inhibition of ABA transport out of the shoots of flooded plants, causing the hormone to accumulate in the leaves.

Control of Stomatal Behaviour by Abscisic Acid which Apparently Originates in the Roots

Zhang, J., Schurr, U. and Davies, W. J. 1987. Control of stomatal behaviour by abscisic acid which apparently originates in the roots.—J. exp. Bot. 38: 1174-1181. Two experiments indicate that abscisic acid (ABA) may influence stomatal behaviour of Commelina communis L. Stomatal conductance could not be correlated with bulk leaf ABA content but when the abaxial epidermis was assayed for ABA, small increases in ABA content correlated well with limitations of leaf conductance. Restricted conductance of the abaxial surface of leaves was associated with an increase of approximately 40 amole ABA per stomatal complex. This agrees with previously published figures. When roots of individual plants were split between two containers, drying the soil around one part of the root system restricted leaf conductance, even though leaf water relations were not affected. Increased ABA content of the epidermis coincided with increased ABA content of the roots in drying soil. Other roots of the same plant in moist soil did not show increased ABA content. These results suggest that in drying soil, ABA can move from the roots to the epidermis and restrict stomatal aperture even when leaf water potentials and turgors remain constant. The importance of this mechanism in providing a sensitive foliar response to decreasing soil moisture is discussed. Key words—Soil drying, ABA, roots, stomata, water relations. Correspondence to: Department of Biological Sciences, University of Lancaster, Bailrigg, Lancaster LAI 4YQ, U.K.

Cadmium-Induced Decrease of Water Stress Resistance in Bush Bean Plants ( Phaseolus vulgaris L. cv. Contender) II. Effects of Cd on Endogenous Abscisic Acid Levels

Summary The cadmium content and the endogenous abscisic acid (ABA) levels of roots, stems, primary, and trifoliate leaves of bush bean plants ( Phaseolus vulgaris L. cv. Contender), grown with different Cd concentrations in the medium were analysed. The samples were taken at different plant growth stages: primary leaf growth stage, first trifoliate leaf growth stage, flowering, and fruit development. No correlation between Cd and ABA contents could be established. In roots Cd-toxicity increased ABA levels. In leaves only the lowest Cd concentration increased the ABA content, while in plants treated with higher Cd concentrations no increase in ABA content in response to wilting was observed. Cd at high concentrations is suggested to decrease water stress resistance by inhibition of the hydroactive stomata response.

REGULATION OF ABSCISIC ACID CONCENTRATION IN LEAVES OF FIELD‐GROWN PEARL MILLET (PENNISETUM AMERICANUM [L.] LEEKE): THE ROLE OF ABSCISIC ACID EXPORT *

SUMMARYDiurnal changes in the concentration of abscisic acid (ABA) which occur in leaves of droughted, field‐grown plants of pearl millet (Pennisetum americanum [L.] Leeke) are not always correlated with changes in bulk leaf water potential (Φ). A rapid decline in ABA content of the leaves following its rise to a peak level in mid‐morning, was observed in several time‐course studies despite continued water stress.The possibility that the reduction in ABA in leaves was due to an elevated rate of its export was examined in two ways: (i) by measuring ABA concentrations in developing panicles (possible sinks for leaf‐produced ABA) and in leaves, and (ii) by comparing the amounts of ABA in ungirdled leaves and in leaves heat‐girdled at the base of the lamina to block export. ABA concentrations in panicles generally paralleled those in leaves, though the peak level of ABA in the morning in panicles occurred later than in the leaves in some samplings. Although girdling initially increased ABA concentration, it did not prevent a subsequent fall which generally paralleled the decline observed in untreated leaves. The decrease in ABA that occurred despite the block to export and despite continuing stress was, therefore, attributed to changes in the synthesis or metabolism of ABA within the leaf.The probable rate of export of ABA from leaves, calculated from the changes in its concentration due to girdling, was highest at the time of most rapid ABA accumulation and declined thereafter. The percentage export of recently assimilated carbon declined similarly. However, the probable absolute rate of export of photosynthate, computed from stomatal conductance and [14C]‐export measurements, was not uniquely related to that of ABA.

Tobacco-mosaic-virus-induced increase in abscisic-acid concentration in tobacco leaves:

The concentrations of free and bound abscisic acid (ABA and the presumed ABA glucose ester) increased three- to fourfold in leaves of White Burley tobacco (Nicotiana tabacum L.) systemically infected with tobacco mosaic virus. Infected leaves developed a distinct mosaic of light-green and dark-green areas. The largest increases in both free and bound ABA occurred in dark-green areas. In contrast, virus accumulated to a much higher concentration in light-green tissue. Free ABA in healthy leaves was contained predominantly within the chloroplasts while the majority of bound ABA was present in non-chloroplastic fractions. Chloroplasts from light-green or dark-green tissues were able to increase stromal pH on illumination by an amount similar to chloroplasts from healthy leaf. It is unlikely therefore that any virus-induced diminution of pH gradient is responsible for increased ABA accumulation. Tobacco mosaic virus infection had little effect on free ABA concentration in chloroplasts; the virus-induced increase in free ABA occurred predominantly out-side the chloroplast. The proportional distribution of bound ABA in the cell was not changed by infection. Treatment of healthy plants with ABA or water stress increased chlorophyll concentration by an amount similar to that induced by infection in dark-green areas of leaf. A role for increased ABA concentration in the development of mosaic symptoms is suggested.

Tobacco mosaic virus-induced increase in abscisic acid concentration in tobacco leaves: intracellular location and relationship to symptom severity and to extent of virus multiplication

Abscisic acid (ABA) concentration was increased 1·1 to five-fold in Samsun tobacco infected with six strains of tobacco mosaic virus (TMV) which produced mosaic symptoms of widely different severity and which multiplied to different extents. The ABA accumulation was more closely related to the severity of mosaic symptoms ( r = 0·93; 4 degrees of fredom, df) than to the extent of virus multiplication ( r = 0·39, 4 df). The increase in ABA concentration was located outside the chloroplast; virus infection had little effect on, or reduced, chloroplastic ABA concentration. Tobacco mosaic virus infection inhibited plant growth. Reduction in growth rate was related both to increase in extrachloroplastic ABA concentration ( r = 0·69, 4 df) and to virus accumulation ( r = 0·73, 4 df). It is concluded that both these factors are important in the inhibition of growth produced by TMV infection.

Effect of Translocation-Hindering Procedures on Source Leaf Photosynthesis in Cucumber

THREE TREATMENTS WHICH ALTERED TRANSLOCATION RATE WERE APPLIED TO CUCUMBER PLANTS: Girdling of source leaf petiole; removal of all aerial sinks; removal of all source leaves except one. Two different effects were observed, one short-term (during the initial 6 hours), and one long-term (detected after several days).The short-term effect was observed exclusively in girdled leaves and involved a reduction in (14)CO(2) fixation rate paralleled by an increase in stomatal resistance. The effects were maximal after 3 hours with subsequent recovery. Stomatal closure apparently resulted from the 5 to 10% water deficit temporarily detected in girdled leaves which probably induced the observed temporary increases in abscisic acid content. Kinetin counteracted the effects of girdling.The long-term effect was detected 3 days after girdling and 3 to 5 days after sink manipulation. An increase or decrease in (14)CO(2) fixation rate was observed when the sink-source ratio was increased or decreased respectively, accompanied by a respective decrease or increase in starch content. Changes in the relative amount of (14)CO(2) incorporated into various photosynthetic products were also observed. Stomatal closure was not involved, and the decrease in CO(2) fixation was not counteracted by kinetin.

Interdependence of growth, water relations and abscisic acid level in Phaseolus vulgaris during waterlogging

The interdependence between changes in growth and water relations after waterlogging was investigated by recording simultaneously growth, transpiration, water potential, turgor, leaf diffusion resistance and abscisic acid content in Phaseolus vulgaris L. cv. bruine Noord‐Hollandse. Growth was inhibited immediately after flooding, whereas transpiration decreased gradually to a low level in about three days. The first two days after flooding a small increase in abscisic acid content in the leaves was observed which was accompanied by an increase in diffusion resistance. The increase in abscisic acid content could result from an inhibited export from the leaves. After the first two days a decrease in water potential and turgor was accompanied by a drastic increase in both abscisic acid content and diffusion resistance. This large increase in abscisic acid content occurred before the turgor had reached its minimum value. The change in diffusion resistance kept showing a lag of about one day with the change in abscisic acid content. The possibility is discussed that besides abscisic acid also its metabolite phaseic acid is involved in stomatal closure. After the formation of adventitious roots on the hypocotyl, abscisic acid level, diffusion resistance, water potential and turgor returned to the control values. Transpiration showed a slow recovery from the sixth day after flooding, whereas growth was inhibited for at least nine days. A remarkable similarity exists between our observations on the responses of bean plants to flooding and the well known responses to drought.

Evidence for panicle control of stomatal baheviour in water-stressed plants of pearl millet

Stomatal conductance ( g s), water potential (ψ), 14C-labelled assimilate export, and abscisic acid (ABA) concentration, were measured in flag leaves hof pearl millet grown in the field in the semi-arid tropics with restricted water supply. At similar ψ, g s increased with progressive stage of development hand growth of the panicle. Flag leaves ixhibited a lower s and rate of 14C-assimilate export, and a higher concentration of ABA, at the boot stage than following panicle emergence. Panicle removal resulted in a reduction in flag leaf 14C-assimilate export when carried out at stigma emergence (panicles just fully emerged from flag leaf sheath), but not when carried out after grain set. Reduction in flag leaf s were detected about 3 days after panicle removal and were correlated with increases in ABA concentration. The increased ABA was not due to any reduction in ψ. Completely blocking assimilate export by heat girdling caused a marked increased in ABA and a reduction in g s. It is suggested that the panicle might stimulate the export of ABA from the flag leaf, so lowering the ABA concentration in the leaf gand facilitating the higher g s found, under water stress, in flowering plants.

DIURNAL CHANGES IN WATER RELATIONS AND ABSCISIC ACID IN FIELD‐GROWNVITIS VINIFERACULTIVARS

SummaryDiurnal changes in endogenous abscisic acid (ABA) in the leaves, together with stomatal conductance and water relations, were studied in grape vines (Vitis viniferaL. cvs Riesling and Silvaner) growing in the field in Adelaide, South Australia.There was an increase in ABA content of the leaves which commenced in the morning and reached a peak of approximately twice the pre‐dawn level at midday. Wilted excised leaves from the same vines accumulated ABA at a higher rate. The increase in attached leaves was sometimes unrelated to low leaf turgor. Import via the xylem may account for this increase during the early part of the day. Leaf conductance in Riesling was high in the early morning but fell as leaf ABA rose, and it is suggested that midday stomatal closure was due to ABA accumulation. Stomatal behaviour later in the day was more readily accounted for by environmental variables such as temperature and atmospheric vapour pressure deficit than by changes in ABA.Abscisic acid did not consistently accumulate in attached leaves in response to zero turgor, even if this condition was maintained for the greater part of the day. It is suggested that loading into the phloem and transport out of the leaf may be important in controlling stress‐induced accumulation of ABA.

The Physiology of a Wilty Pea: Abscisic Acid Production under Water Stress

‘Wilty’ (JI 1069), a mutant of Pisum sativum, has been examined for its ability to produce abscisic acid (ABA) under water stress. ABA was measured using combined gas chromatography-mass spectrometry and multiple-ion-monitoring employing a deuterated internal standard. In intact droughted plants, ‘Wilty’ produced less ABA than a non-wilty line (JI 1194) and maximum production was delayed. Detached leaves of the wilty mutant lost significantly more water than control leaves but did not show an increase in ABA content. Non-stressed mutant material from both intact plants and isolated leaves contained less ABA than control tissue.

The relationship of abscisic acid metabolism to stomatal conductance in Douglas‐fir during water stress

Changes in abscisic acid and its metabolites were followed through two drought cycles in Pseudotsuga menziesii (Mirb.) Franco seedlings to determine the metabolic pathway of the hormone and its relationship to branch (stomatal) conductance. Three year‐old, intact seedlings were water‐stressed, watered, and restressed over a period of 30 days. Water potential was sampled with a pressure chamber and branch conductance with a steady‐state porometer. Needle content of abscisic acid and 2‐trans‐abscisic acid and their saponifiable conjugates were quantified with gas‐liquid chromatography. The typical water potential threshold in branch conductance, decreasing abruptly at ‐2.0 MPa, corresponded to an increase in abscisic acid content of 240 ng g−1. The relationship between abscisic acid and water potential was not definitive, though the general trend was an increase in the hormone with intensifying stress until water potential was ‐5.0 MPa, when concentration sharply declined. No adjustment to stress was observed in the relationships, but stress during the second cycle progressed more slowly. A linear relationship between abscisic acid and its conjugate indicated the importance of the interconversion of the two compounds for storage and supply of the free acid.

Evidence against an intermediary role of abscisic acid in stomatal closure induced by phenylmercuric acetate and faresol

The hypothesis was tested that stomatal closure induced by the antitranspirants phenylmercuric acetate and farnesol is mediated by an increase in abscisic acid content. Isolated leaves of Spinacia oleracea L. cv. Müma, Tradescantia X andersoniana Ludw. et Rohw. and Commelina communis L. were incubated in solutions of phenylmercuric acetate (10−3M) and of farnesol (2 × 10−3M). In all three species, a reduction in stomatal aperture was observed. The extent and velocity of the reaction differed between the species and also between the two compounds applied. The abscisic acid content of the leaves was determined after stomatal closure had been achieved. No significant increase in abscisic acid level was found in treated leaves of Spinacia and Commelina. In Tradescantia, on the contrary, a reduction to about 50% was observed after 120 min treatment. Visible damage of the treated leaves and membrane alterations observable by electron microscopy occurred, especially after treatment with farnesol. These changes in membrane structure suggest a connection with the reduction in stomatal aperture.