Changes In Abscisic Acid Levels Research Articles

Changes in abscisic acid levels in bean leaves during the initial stages of host and nonhost reactions to rust fungi

Changes in abscisic acid (ABA) levels were determined in leaf tissues of French bean ( Phaseolus vulgaris) inoculated with Uromyces appendiculatus var. appendiculatus (pathogenic) and U. vignae (nonpathogenic) using an indirect enzyme-linked immunosorbent assay (ELISA) and HPLC. There was a significant decrease in abscisic acid levels both in leaf tissues and intercellular washing fluids of rust-infected bean leaves at 6 h post inoculation. Similar decreases were induced by both fungi. ABA levels remained low until at least 48 h after inoculation. No evidence was found for production of ABA by differentiated urediospore germlings of either U. appendiculatus or U. vignae. The results suggest that the decrease in ABA levels is a nonspecific result of changes brought about by infection, prior to cell penetration, and that this growth regulator is not a determinant of successful fungal invasion.

The Role of Abscisic Acid in Heat Stress-induced Secondary Dormancy in Apple Seeds

Exposure of stratified apple (Malus domestics Borkh. cv. Golden Delicious) seeds to 30C induces secondary dormancy. To determine if an increase in abscisic acid (ABA) content was associated with the loss in germination capacity, stratified seeds (3,- 6, or 9 weeks at 5C) were held at 30C for 0, 3, or 6 days. Stratification at 5C either had no effect or increased ABA content in embryonic axes, cotyledons, and seed coats. Exposure to 30C after stratification either did not affect or decreased ABA content of embryonic axes and seed coats; in contrast, cotyledonary ABA was increased. Seed coats, cotyledons, and embryonic axes stratified for 3, 6, or 9 weeks at 20C contained the same or higher levels of ABA in comparison with nonstratified seeds or seeds stratified at SC. Changes in ABA levels were not consistently correlated with changes in germination capacity during stratification or after exposure to 30C. These data suggest that changes in ABA are not related to changes in dormancy. Chemical names used: abscisic acid (ABA); butylated hydroxy-toluene (BHT); n-(trichloromethyl) thio-4-cyclohexene-1,2-dicarboximide(Captan).

Participation of auxin and abscisic acid in the regulation of seasonal variations in cambial activity and xylogenesis

The current notion that hormonal level and cell response are clearly correlated has often been challenged recently. During the period of cambial activity, auxin content seems to control the intensity of mitosis and some features of the resulting wood, but not the duration of the active period itself. During cambial rest, the indole-3-acetic acid (IAA) level often remains high in the cambium, but the cell sensitivity to auxin is low. The decrease of auxin transport in autumn is sometimes interpreted as a major qualitative change affecting the pattern of transport, and sometimes as a secondary change occurring later than rest onset. The causes of the seasonal variation of cambial response remain unknown. A hypothesis is proposed that accounts for the structural-functional changes occurring in cambial cells during the onset of dormancy. Abscisic acid (ABA) may reduce wood production and xylem cell enlargement in late summer. An important amount of ABA may be present in the cambial zone in autumn after drought stress and in spring in the young growing shoot. Changes in ABA level do not appear to be clearly correlated with the different steps of cambial rest and activity. Beyond the role of ABA as a stress mediator, its participation in the annual regulation of cambial activity remains unclear. Its distribution in the most alkaline compartments may account for the particularities of its seasonal activity. The involvement of IAA and ABA in cambial growth is discussed within the scope of a possible annual alternation of two different metabolisms in the cambial cell.

A Combined HPLC-ELISA Assay Applied to Measure Abscisic Acid (ABA) and Abscisyl-β-D-Glucopyranoside in Ripening Embryos of Walnut ( Juglans regia L.)

Summary Changes in the amounts of abscisic acid (ABA) and abscisyl-(3-D-glucopyranoside (ABAGE) in embryos of Juglans regia L. were followed during ripening of these organs. ABA and ABAGE were separated by high performance liquid chromatography (HPLC) on a C,8-column and determined by an enzyme-linked immunosorbent assay (ELISA). The ELISA took advantage of the competition between an inert proteinABA conjugate bound to the immunoassay wells and free ABA. About 4 nmol of ABA per g of fresh embryo accumulated during a period in the middle of the 9 to 10week-ripening period. Thereafter, the amounts decreased to about 1 nmol per g in the fully developed embryo. The amounts of ABAGE were generally much lower; changes in ABA levels were not reflected by changes in the amounts of this compound. Tryptophan decarboxylase was induced by ABA, and the accumulation of serotonin in the embryo started when the ABA content reached its maximum.

Effect of drought, on transport and metabolism of abscisic acid in aeroponically grown Helianthus annuus

The effect of drought on transport and metabolism of radioactive abscisic acid (ABA) in roots and shoots of sunflower (Helianthus annuus L. cv. Russian) was observed. Radioactivity from ABA moved freely all over the plants. Young shoot tissues, such as the growing apical bud or axillary buds released from apical dominance, were strong sinks for ABA. Mature tissues were effective exporters. Drought‐induced alterations in the pattern of transport of radioactivity do not appear to be a major factor in the control of drought‐induced changes in ABA levels. Metabolism of ABA occurred in all organs examined in stressed and unstressed plants. Labelled ABA and its metabolites moved in the xylem. Drought altered the quantity of radioactive metabolites and reduced the amount of radioactive ABA in extracts from the stressed plants.

The r�le of abscisic acid in root growth and gravireaction: A critical review

A brief account is given of the discovery of abscisic acid (ABA) in roots and root caps of higher plants as well as the techniques by which ABA may be demonstrated in these tissues. The remainder of the review is concerned with examining the role of ABA in the regulation of root growth. In this regard, it is well established that when ABA is supplied to roots their elongation is usually inhibited, although at low external concentrations a stimulation of growth may also be found. Fewer observations have been directed at exploring the connection between root growth and the level of naturally occurring, endogenous ABA. Nevertheless, the evidence here also suggests that ABA is an inhibitory regulator of root growth. Moreover, ABA appears to be involved in the differential growth that arises in response to a gravitational stimulus. Recent reports that deny a role for ABA in root gravitropism are considered inconclusive. The response of roots to osmotic stress and the changes in ABA levels which ensue, are summarised; so are the interrelations between ABA and other hormones, particularly auxin (e.g. indoleacetic acid); both are considered in the context of the root growth and development. Quantitative changes in auxin and ABA levels may together provide the root with a flexible means of regulating its growth.

Changes in abscisic acid levels during dormancy release in freesia corms

A high level of free-abscisic acid (ABA) was detected when corms were still in deep dormancy. The level of free-ABA decreased as the corm dormancy disappeared and increased temporarily after complete release from dormancy. A gradual slight increase of bound-ABA was observed during dormancy release. Treatment of dormant corms with benzyladenine (BA) increased sprouting but the sprouts did not show normal growth. Ethylene treatment induced complete sprouting and subsequent normal growth. Changes in ABA levels and ethylene production are discussed in relation to dormancy release in freesia corms.

Metabolism of Abscisic Acid in Guard Cells of Vicia faba L. and Commelina communis L.

Metabolism of abscisic acid (ABA) was investigated in isolated guard cells and in mesophyll tissue of Vicia faba L. and Commelina communis L. After incubation in buffer containing [G-(3)H]+/-ABA, the tissue was extracted by grinding and the metabolites separated by thin layer chromatography. Guard cells of Commelina metabolized ABA to phaseic acid (PA), dihydrophaseic acid (DPA), and alkali labile conjugates. Guard cells of Vicia formed only the conjugates. Mesophyll cells of Commelina accumulated DPA while mesophyll cells of Vicia accumulated PA. Controls showed that the observed metabolism was not due to extracellular enzyme contaminants nor to bacterial action.Metabolism of ABA in guard cells suggests a mechanism for removal of ABA, which causes stomatal closure of both species, from the stomatal complex. Conversion to metabolites which are inactive in stomatal regulation, within the cells controlling stomatal opening, might precede detectable changes in levels of ABA in bulk leaf tissue. The differences observed between Commelina and Vicia in metabolism of ABA in guard cells, and in the accumulation product in the mesophyll, may be related to differences in stomatal sensitivity to PA which have been reported for these species.

Postharvest changes in abscisic acid levels in flesh tissue and seeds of Jonathan apples susceptible to storage breakdown

SummaryAnalysis of fruit and seed samples after periods from three to 16 weeks of storage showed that the abscisic acid level in the flesh was maximal early in storage, declining during 16 weeks at —1°C. A direct correlation between ABA level and later breakdown incidence was present early in storage, the correlation being greatest after five weeks, much earlier than the appearance of visible symptoms. In the seeds ABA was maximal after three weeks and then declined, being undetectable by 12 weeks. However, there was no significant correlation between seed ABA content and breakdown incidence. When early seed extracts were injected into fruit, breakdown incidence increased but the increase was unrelated to the fruit source of the seeds.

Abscisic Acid and its ß-D-Glucopyranosyl Ester in Saplings of Scots Pine (Pinus sylvestris L.) in Relation to Water Stress

Summary In different shoot parts of Scots pine saplings abscisic acid (ABA) and its s-D-glucopyranosyl ester (ABA-glu) have been identified by chromatographical methods and mass spectrometry. Changes in the endogenous levels of ABA and its main metabolite ABA-glu have been determined by gas chromtography in relation to water stress (1, 2 and 4 h) and rewatering (30 min and 4 h). At the beginning of water stress ABA increased in young shoots and the needles of older parts, but decreased in the axis. Simultaneously an ABA-glu peak occurred especially in the needles indicating that both ABA biosynthesis and metabolism are stimulated by water stress. During 30 min rewatering the ABA level increased in all shoot parts, most intensively in the axis. From the results obtained it can be concluded that the increase of free ABA level at the beginning of water stress is based mainly on ABA biosynthesis, whereas during rewatering a partial re-activation of ABA-glu might be involved.

Changes in phenolic acids and abscisic acid in sugar pine embryos and megagametophytes during stratification

The phenolic acids and abscisic acid (ABA) of sugar pine (Pinus lambertiana Dougl.) embryos and megagametophytes, separated by high‐pressure liquid chromatography, were analyzed during 90 days stratification of the seeds. The phenolic acids occurred mainly as glycosides. Following hydrolysis, the majority of phenolics present could be identified as common benzoic and ciranamic acid derivatives. Levels of phenolic acids were relatively low in dormant seeds, but increased substantially in the embryos during stratification at 5°C, particularly cinnamic acid, p‐coumaric acid, ferulic acid, and one unknown. This active synthesis during stratification did not support an inhibitory function for phenolic acids. During stratification at 5°C, changes in ABA levels in both tissues followed a triphasic pattern, with no loss during the first 30 days, a significant decrease the second 30 days, and a lesser decrease the last 30 days. Loss of ABA from moist seeds at 25°C occurred three times as rapidly, so that by 30 days the ABA level of these seeds was equivalent to that of seeds stratified 90 days at 5°C; however, dormancy was not alleviated at 25°C. Application of exogenous ABA (10−7 to 10−4M) to stratified seeds did not significantly reduce germination. Together, the above results did not support a primary role for ABA in the maintenance of dormancy in sugar pines.A correlated increase in phenylpropanoid metabolism and respiratory capacity with increased germinability during stratification suggests that loss of dormancy may be more closely dependent on increased levels of growth promoters or shifts in metabolic pathways.

Abscisic Acid and the Photoperiodic Induction of Dormancy in Salix viminalis L

A series of growth room experiments was carried out aiming to establish the role of abscisic acid on dormancy of Salix viminalis L. The inhibitor content and abscisic acid levels of extracts from roots, sap, leaves, and apical tissues of willow were measured using biological assay and gas-liquid chromatography.No evidence was obtained that photoperiodically mediated dormancy is associated with changes in abscisic acid levels or beta-inhibitor activity.