Chapter 22 Abscisic acid perception and transduction

Abstract

The phytohormone abscisic acid (ABA) plays an important role in many physiological processes in plants. This hormone is necessary for regulation of several events during late seed development and is crucial for the response to environmental stresses such as desiccation, salt and cold. Important advances have been made in understanding the pathways that induce ABA and how the ABA signal is transduced into physiological responses. Investigation of the response of guard cells to ABA has yielded important information about ABA regulated ion channels involved in ABA signal transduction. The study of gene expression in response to ABA and stress has led to the detection of several intermediates of the ABA signal cascade. ABA induces the transcription of many genes and dissection of ABA responsive promoters has given new insight into the integration of ABA into stress response and seed development. Several ABA and stress responsive cis-elements have been identified and the interactions between these elements are being investigated. An important part of the physiological response to ABA is achieved through de novo gene expression. Many genes, which are expressed in late embryo development, can be induced by exogenous ABA treatment in embryo and vegetative tissues. However, ABA seems to be a prerequisite for gene expression but the wild type level is far in excess of the necessary concentration.