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.     

Concentrations of Abscisic Acid and Indole-3-Acetic Acid in Soybean Seeds during Development

Concentrations of abscisic acid (ABA) and indole-3-acetic acid (IAA) in seed parts were determined during reproductive development of soybean plants (Glycine max [L.] Merr. cv `Chippewa 64'). The concentration of ABA and IAA changed independently in individual seed parts with time. Measurement of the level of ABA and IAA in whole seeds masked the changes which occurred in individual seed tissues. The concentration of ABA was generally highest and that of IAA was generally lowest in the embryonic axis of soybean seeds. In the testa, the IAA concentration was generally highest while the ABA concentration was generally the lowest compared to other parts of the seed.     

Regulation of Soybean Embryogenesis by Abscisic Acid

Abscisic Acid (ABA) stimulates growth and protein accumulationin soybean (Glycine max. L. Merr.) embryos during the earlyphases of embryogenesis. Growth of mid-stage embryos is suppressedby ABA, but protein accumulation is not impaired. Metabolitedistribution studies indicate that ABA alters partitioning ofsucrose in older embryos such that protein accumulation is sustainedat the expense of lipid accumulation. The responses of in vitrocultured embryos to ABA is consistent with the normal patternof ABA accumulation and disappearance that occurs during embryogenesisin situ. A close correlation exists between ABA levels and embryogrowth rates in situ in three cultivars of soybeans. Dependingon the age or stage of the developing embryo, ABA either servesto promote or inhibit embryo growth. Key words: Embryogenesis, ABA, Seeds, Soybean.     

Movement and Endogenous Levels of Abscisic Acid during Water-Stress-induced Abscission in Cotton Seedlings

In an effort to investigate possible involvement of abscisic acid (ABA) in foliar abscission processes, its movement and endogenous levels were examined in cotyledons taken from cotton seedlings (Gossypium hirsutum L.) subjected to varying degrees of water deficit, a condition which initiates leaf abscission. Using a pulse-labeling technique to avoid complications of uptake and exit from the tissue, ABA-1-¹⁴C movement was observed in both basipetal and acropetal directions in cotyledonary petioles taken from well watered, stressed, and rewatered plants. The label distribution patterns obtained after 1 and 3 hours of transport under all situations of water supply were diffusive in nature and did not change when tested under anaerobic conditions. The transport capacity of the petioles ranged from 3.6 to 14.4% ABA-1-¹⁴C transported per hour at estimated velocities of 0 to 2 millimeters per hour. Comparison of basipetal and acropetal movement indicated a lack of polarity under all conditions tested. These low transport capacities and slow velocities of movement, when compared to the active transport systems associated with auxin movement, as well as the lack of anaerobic effects and polarity, suggest that ABA movement in cotton cotyledonary petiole sections is facilitated by passive diffusion. Increases in free and bound ABA in the lamina with increased water stress did not correlate with patterns of cotyledonary abscission. Thus, no evidence was found to suggest that ABA is directly involved in stress-induced abscission processes.     

Leaf Senescence and Abscisic Acid in Leaves of Field-grown Soybean

Leaf senescence in field-grown soybean (Merrill) as defined by the period after full expansion, was studied by measuring abscisic acid (ABA), total soluble protein, and chlorophyll in leaves through the later part of the growing season. ABA concentrations increased significantly at the end of the season when leaves had started to turn yellow, well after total soluble protein and chlorophyll had started to decline. The results indicate that events occurring before leaf yellowing are more significant in evaluating leaf senescence since the yellowing condition and rise in ABA are effects of changes in physiological activity beginning when leaves are still green.     

Abscisic Acid Negatively Regulates Expression of Chlorophyll a/b Binding Protein Genes during Soybean Embryogeny

The levels of abscisic acid (ABA) during embryogenesis in the soybean (Glycine max) cultivar Dare were quantitated. An increase in the quantity of ABA per cotyledon was correlated with a decrease in the chlorophyll a/b binding (Cab) protein gene mRNA population. Soybean cotyledons were cultured in vitro in the presence or absence of ABA. Quantitation of cotyledonary ABA levels and Cab mRNA levels indicated that the application of 5 × 10⁻⁵ molar and 5 × 10⁻⁶ molar exogenous ABA decreased Cab mRNA prevalences. S1 nuclease protection experiments demonstrated that exogenous ABA modulated the level of Cab3 mRNA. These data strongly suggest that one of the developmental regulators of Cab gene expression during soybean embryogeny is the plant hormone, ABA; ABA negatively regulates Cab mRNA accumulation.     

Seed Development in the Recalcitrant Species Quercus robur L: Water Status and Endogenous Abscisic Acid Levels

Water status and endogenous ABA levels were measured duringthe development of the embryonic axis and cotyledons in fruitsof Quercus robur L. As dry matter accumulated in the embryoduring development, both moisture content and osmotic potential(     

Seasonal Levels of Abscisic Acid in Buds and Stems of Acer saccharum

Changes in abscisic acid (ABA) were followed in the buds and youngest stems of 6-year-old sugar maple (Acer saccharum Marsh.) saplings at approximately monthly intervals during the year. High levels present in the buds in July and August showed a moderate decline through early October, but subsequently increased following leaf fall and reached the maximum values detected during the study in November and December. Thereafter ABA fell sharply, reaching its lowest point immediately prior to budbreak in early May. While ABA in the stems followed a somewhat similar pattern, only minor changes were observed in the relatively low values detected between June and November. Except for the spring months, when concentrations of ABA in the stems and buds were at minimum levels, the buds always contained several times more inhibitor per unit dry weight of tissue. Analysis of selected samples from both tissues showed that bound (alkaline-hydrolyzable) ABA increased during the overwintering season, with the highest values noted in the spring. Although the patterns of change observed in this study are indicative of a role for ABA in the overwintering process, ABA does not appear to be the primary endogenous factor responsible for initiation of the dormant state.     

Abscisic Acid Simultaneously Decreases Carboxylation Efficiency and Quantum Yield in Attached Soybean Leaves

Injecting abscisic acid (ABA) into the petiole of attached soybeanleaves simultaneously decreased quantum yield and carboxylationefficiency. These decreases were proportional to the accompanyingdecrease of light-saturated photosynthetic rate under normalatmosphere. ABA did not affect the CO² compensation point atsaturating irradiance, or the stimulation of net photosynthesisproduced when the partial pressure of oxygen was reduced from210 to 20 mPa Pa^–1 at a rate-limiting irradiance. Thedecreased carboxylation efficiency could not be attributed toa deactivation of RuBP carboxylase since the activation statusof the enzyme in leaves was insensitive to ABA. Although photosyntheticcapacity was decreased, the content of RuBP present was increasedin leaves treated with ABA at saturating irradiance and normalatmosphere. The increase in RuBP content was proportional tothe corresponding inhibition of photosynthetic capacity. Followingexposure to incident irradiances close to the light compensationpoint, the photosynthetic rate of ABA-treated leaves did notincrease when exposed to a subsequent increase of irradiancein the light-limited range. This response was not due to stomatalclosure. Key words: Abscisic acid, quantum yield, RuBP, RuBP carboxylase, carboxylation efficiency     

The Stability of Conjugated Abscisic Acid during Wilting

Tomato and silverbeet shoots that had been fed (±)-[2-¹⁴C]abscisicacid (ABA) some days previously did not hydrolyse their alkali-saponifiable[¹⁴C]ABA fraction when they wilted. The content of alkali-saponifiableABA in untreated plants did not fall on wilting so the endogenousconjugate is not hydrolysed either. In tomato and silverbeet,therefore, conjugation of ABA is irreversible.     

植物ABA受体及其介导的信号转导通路

ABA是调控植物体生长发育和响应外界应激的重要植物激素之一。近年来, ABA受体的筛选和鉴定取得了突破性进展, 为植物中ABA信号转导通路的阐明奠定了重要基础。该文主要综述了ABA-binding protein/H subunit of Mgchelatase (ABAR/CHLH)、G protein-coupled receptor 2 (GCR2)、GPCR-type G protein 1/2 (GTG1/2)和pyrabactin resistant/PYR-like/regulatory component of ABA (PYR/PYL/RCAR)被报道为ABA受体的研究历程, 重点介绍了以ABAR/CHLH PYR/PYL/RCAR为受体的ABA信号转导通路模型的构建, 旨在为ABA受体及其信号转导通路的相关研究提供参考。     

Chemistry of Abscisic Acid, Abscisic Acid Catabolites and Analogs

Recently there have been breakthroughs on a number of fronts in abscisic acid (ABA) biology research that have advanced the field significantly, including discovery of genes involved in ABA metabolism, along with progress in understanding of ABA signaling (Finkelstein and others 2002; Kushiro and others 2004; Lim and others 2005; Saito and others 2004). At the same time, the chemistry of ABA has advanced. New analytical methods have been developed for profiling ABA and catabolites (Ross and others 2004; Zaharia and others 2005). Novel bioactive catabolites have been discovered from feeding studies with deuterated ABA and catabolites (Zaharia and others 2004; Zhou and others 2004). This review covers recent advances and prospects in natural products chemistry, analysis of ABA catabolism, and applications of ABA analogs for biochemical studies and horticultural uses.     

Distribution of Abscisic Acid in Maize Kernel during Grain Filling

The distribution of abscisic acid (ABA) within maize (Zea mays L.) kernels was studied in kernels from nontreated plants, from plants in which assimilate supply had been altered by source/sink manipulations, and in kernels cultured in vitro on ABA-free media. Prior to growth of the embryo, both the pedicel/placento-chalazal complex and the endosperm contained high concentration of ABA; however, the quantity of ABA in these tissues declined as the concentration in the embryo increased during the early stages of embryo growth. Peaks in the levels of ABA appeared to occur prior to and not concurrent with physiological events during grain filling. During most of the grain filling period, ABA concentration in the embryo was higher than that found in other kernel components. Altering assimilate supply by partial defoliation at two stages of development resulted in variable and transient effects on the relative distribution and concentration of ABA in kernel components. The concentration and distribution of ABA among components of kernels grown in vitro was similar to that observed for field-grown kernels. On the basis of these findings, in situ synthesis of ABA by kernel components is implicated and the putative role of ABA in the regulation of kernel development is discussed.     

热胁迫对不同发育阶段大豆生长素和脱落酸含量的影响(英文)

大豆等植物体内细胞受热或受其它理化因素（如：重金属离子、乙醇、氨基酸类似物）、以及缺氧、DNA损伤、病毒感染等病理因素刺激后,促发应激反应,启动某些基因表达,能产生各种生理活性物质以及各种酶类,共同调控代谢过程和某些激素的活动,如：吲哚乙酸（IAA）、脱落酸（ABA）等。这些内源IAA和ABA共同作用,调节着大豆的抗逆性,从而影响着大豆的农艺性状。本试验对华北生态型的六个大豆栽培种,进行热激处理;取其第三片展开叶,测其内源IAA和ABA含量。这些品种分别是：早熟17,诱处4号,诱变31,耐阴黑豆、科丰6号和科丰34（Tan．1）。初花期,第一天热激（43～45℃,4h）后,它们的IAA和ABA水平均显著高于对照（30～33℃）（Fig．1）。然而,在连续一天热激后（43～45℃,4h／d）,大多数品种的IAA和ABA比第一天减少（Fig．2）。盛花期连续热激处理二天（43～45℃,4h／d）,IAA水平一般低于对照（3～33℃）,半数品种ABA水平也低于对照（Fig．3）。结荚期连续两天热激后（45℃,4h／d）,IAA和ABA含量均显著高于对照（30～33℃）（Fig．4）。     

Changes in Abscisic Acid Levels in Developing Grains of Wheat (Triticum aestivum L.

ABA has been determined in wheat grains during their development. The maximum level of ABA occurred approximately 7 weeks afterear emergence (40 d after peak anthesis). This level subsequentlyfell sharply as a result of metabolism of the ABA by the maturinggrains.     

NaCI Reduces Indole-3-Acetic Acid Levels in the Roots of Tomato Plants Independent of Stress-Induced Abscisic Acid

Indole-3-acetic acid (IAA) was measured in leaves and roots of tomato (Lycopersicon esculentum) genotypes subjected to salt stress. An abscisic acid (ABA)-deficient mutant of tomato (sitiens), the genetic parent (Rheinlands Ruhm, RR), and a commercial variety (Large Cherry Red, LCR) of tomato were treated with 50 to 300 mM NaCl in nutrient culture. Both LCR and RR had significantly higher levels of IAA in the roots compared with that in sitiens prior to treatment. The initial levels of IAA in the roots of LCR and RR declined by nearly 75% after exposure to NaCl, whereas those in roots from the sitiens mutant remained unchanged. IAA levels in the leaves of all genotypes remained unchanged or increased slightly in response to NaCl. ABA was highest in leaves from the normal genotypes after exposure to NaCl. ABA levels in the roots of sitiens were similar to the levels in the normal genotypes, whereas levels in the leaves were only 10% of the levels found in normal genotypes regardless of the salt treatment. Treatment of LCR and sitiens with exogenous ABA increased the ABA levels in leaves and roots, but there were no measurable changes in endogenous IAA. Therefore, the reduction in IAA appears to result from an ABA-independent effect of NaCl on IAA metabolism in the roots of stressed plants.     

Water Content during Abscisic Acid Induced Freezing Tolerance in Bromegrass Cells

Changes in water content and dry weight were determined in control cells and those induced to cold harden in response to abscisic acid (ABA) treatment (7.5 × 10⁻⁵ molar). Bromegrass (Bromus inermis Leyss cv Manchar) cells grown in suspension culture at room temperature (23°C) for 7 days acclimated to −28°C (LT₅₀) when treated with ABA, or to −5°C when untreated. ABA significantly reduced cell growth rates at 5 and 7 days after treatment. Growth reduction was due to a decrease in cell number rather than cell size. When the cell water content was expressed as percent water (percent H₂O) or as grams water per gram dry weight (gram H₂O/gram dry weight [g DW]), the water content of hardy, ABA-treated cells decreased from 85% to 77% or from 6.4 to 3.3 g H₂O/g DW in 7 days. Control cell water content remained static at approximately 87% and 7.5 g H₂O/g DW. However, cell water content, expressed as milligrams water per million cells (milligram H₂O/10⁶ cells), did not differ in ABA-treated or control cells. The dry matter content of ABA-treated cells, expressed as milligram DW/10⁶ cells increased to 3.3 milligram/10⁶ cells in 7 days, whereas the dry weight of the control cells remained between 1.4 to 2.1 milligrams/10⁶ cells. The osmotic potential of ABA-treated cells decreased by the fifth day while that of control cells increased significantly and then decreased by day 7. Elevated osmotic potentials were not associated with increased ion uptake. In contrast to much published literature, these results suggest that cell water content does not decrease in ABA-treated cells during the induction of freezing tolerance, rather the dry matter mass per cell increased. Cell water content may be more accurately expressed as a function of cell number when accompanying changes to dry cell matter occur.