Vascular system is a node of systemic stress responses: Competence of the cell to synthesize abscisic acid and its responsiveness to external cues

Activation of abscisic acid (ABA) biosynthesis is a trigger to elicit ABA-mediated biological events. We recently reported that drought-induced ABA biosynthesis occurs predominantly in vascular parenchyma cells. This work also showed that a particular set of drought inducible gene expressions initiated in the vascular system. The spatial constraint of ABA biosynthesis is supposed to be critical for directing systemic stress responses. Cellular competence to synthesize ABA and its responsiveness to developmental and environmental signals is discussed.Key words: abscisic acid, biosynthesis, competence, responsiveness, vascular systemPlants live in a changing environment by optimizing their growth to given external cues. Among such environmental factors, regulation of water status is essential for plant life. Plant cells have machinery to adapt to the drought stress for itself as well as adaptation machinery to protect other cells by generating mobile signals to distal organs. Abscisic acid (ABA) is one of such mobile signals in which signaling and metabolic pathways are well documented. When subjected to drought stress, plants activate both ABA-dependent and ABA-independent cascades, and in turn induce the expression of large number of stress responsive genes and post-translational modifications.¹ Endo et al.,² demonstrated that vascular parenchyma cells play a key role in the activation of ABA-dependent pathway via producing drought-induced ABA.² This work also showed that the subset of drought stress-responsive genes was induced earlier in the vascular tissues than in mesophyll tissues.²