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Osmotic Stress-Induced Polyamine Accumulation in Cereal Leaves ¹

II. Relation to Amino Acid Pools

ARCO Plant Cell Research Institute, Dublin, California 94568, Department of Biology, Yale University, New Haven, Connecticut 06511

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, glutamic acid decreases with a corresponding rise in glutamine. Difluoromethylarginine (0.01-0.1 millimolar), the enzyme-activated irreversible inhibitor of arginine decarboxylase, prevents the stress-induced putrescine rise, as well as 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 -difluoromethylarginine is suggested as probes for the physiological significance of stress responses by plant cells.

¹ Supported by National Institutes of Health Grant No. AG 02742 to A. W. Galston, and American Cancer Society Summer Fellowship to H. E. Flores.