Regulation of Bud Rest in Tubers of Potato, Solanum tuberosum L: VI. Biochemical Changes Induced in Excised Potato Buds by Gibberellic Acid.

The rest period of the potato tuber was studied in relation to certain biochemical changes that are induced by gibberellic acid (GA(3)). The concentration of reducing sugars in excised plugs with buds treated with 10(-4)m GA(3) decreased in the first 4 hours after treatment and then rapidly increased up to 70 hours. The pattern in control buds was similar, but the changes occurred more slowly. The response to GA(3) is temperature-dependent and is not limited to any particular tissue of the tuber. The concentration of reducing sugars in excised buds increased proportionally to the log of the concentration of GA(3) in a range from 10(-8) to 10(-4)m. At 10(-3)m, GA(3) slightly inhibited production of reducing sugars. Malonate inhibits the initial decrease and the subsequent increase in reducing sugars in control buds, but not the increase induced by GA(3).Total protein in buds was not influenced by 10(-4)m GA(3) over a period of 40 hours, nor did activity of alpha-amylase increase significantly until 20 hours after beginning of treatment. Invertase activity was present initially and, in the presence of GA(3), increased after 20 hours. GA(3) had no effect on starch phosphorylase activity, which was always present and remained steady over the 20-hour test period.In short term experiments the rate of protein synthesis and synthesis of specific protein fractions were not affected by 10(-4)m GA(3), as measured by the incorporation of l-phenylalanine-U-(14)C or by experiments with (14)C- and (3)H- labeled l-phenylalanine or l-leucine.