Plant responses to drought, from ABA signal transduction events to the action of the induced proteins

The plant hormone abscisic acid (ABA) is necessary for the regulation of several aspects during seed development and for the response to environmental stresses such as desiccation, salt and cold. An important part of the physiological response to ABA is achieved through gene expression. Although different signal molecules have been identified, the signal transduction pathway from ABA perception to the induction of specific genes is not very well established yet. In particular, phosphorylation and dephosphorylation events have been identified as important in ABA signalling. A great effort has been focused on analysing the promoters of ABA-responsive genes in order to identify cis- and trans-acting elements that mediate transcriptional regulation. Many different proteins accumulate in response to water deficit, some of them with a clear function in protecting the cells against dehydration. Other proteins, whose function is not completely understood, include LEA proteins that accumulate during late embryogenesis and in response to ABA. (C) Elsevier, Paris.