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 se veral aspects during seed development and for the response to environmental stresses such as desiccation, salt and cold. An important part of the phys iological response to ABA is achieved through gene expression. Although dif ferent signal molecules have been identified, the signal transduction pathw ay from ABA perception to the induction of specific genes is not very well established yet. In particular, phosphorylation and dephosphorylation event s have been identified as important in ABA signalling. A great effort has b een focused on analysing the promoters of ABA-responsive genes in order to identify cis- and trans-acting elements that mediate transcriptional regula tion. 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 p roteins that accumulate during late embryogenesis and in response to ABA. ( C) Elsevier, Paris.