Osmotic Stress-Induced Polyamine Accumulation in Cereal Leaves

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Abstract
Arginine decarboxylase activity increases 2-3 fold in osmotically stressed oat leaves in both light and dark, but putrescine accumulation in the dark is only 1/3-1/5 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. Precursor amino acid availability is limiting to the stress response. Amino acid levels change rapidly upon osmotic treatment; notably, glutamic acid decreases with a corresponding rise in glutamine. Difluoromethylarginine (0.01-0.1 mM), enzyme-activated irreversible inhibitor or arginine decarboxylase, prevents the stress-induced putrescine rise, and the incorporation of label from [14C]arginine 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 .alpha.-difluoromethylarginine is suggested as probes for the physiological significance of stress responses by plant cells.