Differential involvement of abscisic acid in dehydration and osmotic stress in rice cell suspension

Abstract

Plant cells react to different environmental stimuli in different ways. The plant growth regulator abscisic acid (ABA) has been reported to be produced and involved in stress responses. To understand the role of ABA in relation to stress responses, we chose the ABA‐induced RAB (responsive to ABA) gene as a marker to study both dehydration and osmotic‐induced stress responses in rice cell suspensions. The kinetics of RAB gene expression under ABA, dehydration and mannitol treatments were studied. Dehydration‐induced RAB expression was slower as compared to both ABA‐ and mannitol‐induced RAB gene expression. Under dehydration conditions, the expression of RAB gene was correlated with an increase in endogenous ABA levels. Inhibition of protein or ABA synthesis prevented RAB expression under dehydration treatment. Under mannitol treatment, the RAB mRNA accumulated as fast as with ABA treatment, though there was no endogenous ABA accumulation. Inhibition of protein synthesis had no effect on mannitol‐induced RAB gene expression. Proton pump inhibitor, calcium channel and outward rectifying potassium channel blockers reduced both dehydration‐ and mannitol‐induced RAB gene expression. The potassium channel blocker BaCl2 reduced mannitol‐induced RAB gene expression while it had no effect on dehydration‐induced RAB gene expression. The possible differences in signal transduction between dehydration and osmotic stress are discussed.