Osmotic Stress-Induced Polyamine Accumulation in Cereal Leaves

Abstract

Arginine decarboxylase activity increases 2- to 3- fold in osmotically stressed oat leaves in both light and dark, but putrescine accumulation in the dark is only one-third to one-half of that in light-stressed leaves. If arginine or ornithine are supplied to dark-stressed leaves, putrescine rises to levels comparable to those obtained by incubation under light. Thus, precursor amino acid availability is limiting to the stress response. Amino acid levels change rapidly upon osmotic treatment; notably, glu- tamic acid decreases with a corresponding rise in glutamine. Difluoro- methylarginine (0.01-0.1 millimolar) the enzyme-activated irreversible inhibitor of arginine decarboxylase, prevents the stress-induced putres- cine rise, as well as the incorporation of label from ['4Curginine, with the expected accumulation of free arginine, but has no effect on the rest of the amino acid pool. The use of specific inhibitors such as a-difluoro- methylarginine is suggested as probes for the physiological sigificance of stress responses by plant cells.