Polyamine Metabolism and Osmotic Stress

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Abstract
We have attempted to improve the viability of cereal mesophyll protoplast by pretreatment of leaves with DL-.alpha.-difluoromethylarginine (DFMA), a specific ''suicide'' inhibitor of the enzyme (arginine decarboxylase) responsible for their osmotically induced putrescine accumulation. Leaf pretreatment with DFMA before a 6 hour osmotic shock caused a 45% decrease of putrescine and a 2-fold increase of spermine titer. After 136 hours of osmotic stress, putrescine titer in DFMA-pretreated leaves increased by only 50%, but spermidine and spermine titers increased dramatically by 3.2- and 6-fold, respectively. These increases in higher polyamines could account for the reduced chlorophyll loss and enhanced ability of pretreated leaves to incorporate titriated thymidine, uridine, and leucine into macromolecules. Pretreatment with DFMA significantly improved the overall viability of the protoplast isolated from these leaves. The results support the view that the osmotically induced rise in putrescine and blockage of its conversion to higher polyamines may contribute to the lack of sustained cell division in cereal mesophyll protoplasts, although other undefined factors must also play a major role.