STARCH-ACCUMULATING SWEET-POTATO CALLUS-TISSUE DEVOID OF BETA-AMYLASEBUT WITH 2 STARCH PHOSPHORYLASE ISOZYMES

By controlling the concentrations of kinetin, auxin, and sucrose in th e Murashige-Skoog medium, starch contents in callus culture induced fr om sweet potato tissues could be manipulated. Activity staining and We stern analysis on PAGE plates and activity assays made on starch phosp horylase in the presence and absence of mercuric ions showed that beta -amylase is absent in callus cultures regardless of whether their star ch content is high or low. This would imply that beta-amylase inductio n in sweet potato calli is not linked to the metabolic control through which the expression of storage function is associated, as proposed b y Nakamura et al. [Plant Physiol., 96, 902 (1991)] for sweet potato le af-petiole cuttings. Analyses of starch phosphorylase in crude extract s suggested the presence of a new starch phosphorylase in tuberous roo t and callus tissue. This phosphorylase is immunologically different f rom the tuberous root and leaf enzymes that we studied previously.