Role of putrescine in enhancing shoot elongation in Scirpus mucronatus under submergence

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Abstract
Changes in polyamine biosynthesis in relation to submergence‐enhanced shoot elongation were determined in shoots of Scirpus mucronatus L. Under submergence, the levels of free putrescine and the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17) increased, but the levels of free spermidine and spermine and the activity of S‐adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50) decreased. The increases in free putrescine and shoot elongation in submerged shoots diminished from the base to the apex. The increase in free putrescine in submerged shoots was coincident with the increase in shoot length. The submergence‐induced increases in free putrescine and shoot elongation were inhibited by both 5 μMa‐difluoromethylarginine and 5 μMa‐difluoromethylornithine, and the inhibitory effects were reversed by 50 μM putrescine. These overall results indicate that ADC‐ and ODC‐mediated putrescine synthesis is essential for the elongation of Scirpus shoots grown under submergence.