We have previously determined that phospholipase D (PLD) is activated by abscisic acid (ABA), and this activation is required for the ABA response of the cereal aleurone cell. In this study, ABA-stimulated PLD activity was reconstituted in vitro in microsomal membranes prepared from aleurone protoplasts. The transient nature (20 min) and degree (1.5- to 2-fold) of activation in vitro were simil...

The plant hormone abscisic acid (ABA) regulates many key processes involved in plant development and adaptation to biotic and abiotic stresses. Under stress conditions, plants synthesize ABA in various organs and initiate defense mechanisms, such as the regulation of stomatal aperture and expression of defense-related genes conferring resistance to environmental stresses. The regulation of stom...

The hormone abscisic acid (ABA) regulates stress responses and developmental processes in plants. Calcium-permeable channels activated by reactive oxygen species (ROS) have been shown recently to function in the ABA signaling network in Arabidopsis guard cells. Here, we report that ABA activation of these I(Ca) Ca(2)+ channels requires the presence of NAD(P)H in the cytosol. The protein phospha...

Phytohormones have essential roles in coordinately regulating a large array of developmental processes. Studies have revealed that brassinosteroids (BRs) and abscisic acid (ABA) interact to regulate hundreds of expression in genes, governing many biological processes. However, whether their interaction is through modification or intersection of their primary signaling cascades, or by independen...

The endogenous messenger, the phytohormone abscisic acid (ABA) plays a major role in plant's adaption to drought, salinity, cold and other abiotic stresses. In addition to abiotic stress signaling, ABA is involved also in developmental regulation and in responses to diverse biotic stresses. Dehydration stress results in a strong increase in endogenous ABA levels, which can be perceived by RCAR/...

We have previously shown that the Arabidopsis (Arabidopsis thaliana) RING-H2 E3 ligase RHA2a positively regulates abscisic acid (ABA) signaling during seed germination and postgerminative growth. Here, we report that RHA2b, the closest homolog of RHA2a, is also an active E3 ligase and plays an important role in ABA signaling. We show that RHA2b expression is induced by ABA and that overexpressi...

Many biochemical approaches show functions of calcium-dependent protein kinases (CDPKs) in abscisic acid (ABA) signal transduction, but molecular genetic evidence linking defined CDPK genes with ABA-regulated biological functions at the whole-plant level has been lacking. Here, we report that ABA stimulated two homologous CDPKs in Arabidopsis thaliana, CPK4 and CPK11. Loss-of-function mutations...

The phytohormone abscisic acid (ABA) regulates the expression of many genes in plants; it has critical functions in stress resistance and in growth and development. Several proteins have been reported to function as ABA receptors, and many more are known to be involved in ABA signalling. However, the identities of ABA receptors remain controversial and the mechanism of signalling from perceptio...

Experiments were designed to obtain evidence about the possible role of xanthophylls as abscisic acid (ABA) precursors in water-stressed leaves of Phaseolus vularis L. Leaves were exposed to (14)CO(2) and the specific activities of several major leaf xanthophylls and stress-induced ABA were determined after a chase in (12)CO(2) for varying periods of time. The ABA specific radioactivities were ...

Plants are frequently exposed to numerous environmental stresses such as dehydration and high salinity, and have developed elaborate mechanisms to counteract the deleterious effects of stress. The phytohormone abscisic acid (ABA) plays a critical role as an integrator of plant responses to water-limited condition to activate ABA signal transduction pathway. Although perception of ABA has been s...