Effect of gamma irradiation on indole acetic acid synthesizing system in potatoes

Abstract

The sprout inhibition of potato achieved by 10 Krad gamma irradiation can be completely reversed by treatment of the tubers with 20 ppm IAA. Studies on the level of IAA synthesizing system in unirradiated and irradiated potatoes showed that on irradiation the enzyme activity steadily decreased and fell to zero at the end of 5 weeks storage. When irradiated potatoes were soaked with 20 ppm of IAA, the loss in enzyme activity was not discernible but, with tryptophan, there was no protection of enzyme activity. The enzyme was purified 12 fold, from control and from irradiated potatoes immediately after irradiation. The product of the reaction was identified as IAA by co-chromatography with authentic sample. The reaction required pyridoxal phosphate and a keto acid. Among the keto acids, α-ketoglutaric acid and phenylpyruvic acid were the best as substrates. The optimum pH for the reaction was 8, and optimum temperature was 37°. The two enzyme preparations differed in their response to substrates and co-enzymes; the Michaelis constant for tryptophan was 6 × 10 −4 M for the enzyme from control and 4 × 10 −4 M for enzyme from irradiated potatoes. The reaction was inhibited by NH 2OH, INH and EDTA. Inhibition by EDTA was reversed by Mn ++.