STARCH TRANSFORMATION DURING BANANA RIPENING: I — THE PHOSPHORYLASE AND PHOSPHATASE BEHAVIOR IN MUSA ACUMINATA

Starch levels as well as the phosphorylases and acid phosphatase activity during ripening of the banana fruit was investigated. The concentrations and sequence of appearance of sucrose, glucose and fructose were determined by use of specific enzymatic reactions. During the climacteric period, the phosphatase activity increased while phosphorylase activity, which initially increased before starch transformation began, thereafter decreased in a complex pattern. The starch was transformed into sucrose with later formation of glucose and fructose. Four bands of phosphorylase multiple forms, detected electrophoretically, did not change during ripening. One of them was able to synthesize a branched starch-using amylose as a primer and glucose 1 -phosphate as the substrate. Banana slices were infiltrated with water or solutions of cycloheximide or actinomycin D. Inhibition of phosphatase-induced activity was recorded only in the cycloheximide group. No change in phosphorylase activity was detected in any of these infiltrated groups. Sucrose production from starch was partially inhibited both by actinomycin D and cycloheximide. The aformentioned results were interpreted as indicating the previous presence of phosphorylase in the preclimacteric phase without new synthesis during ripening. The increase of activity of phosphatase was probably due to ribosomal synthesis rather than to nucleic acid synthesis.