EFFECTS OF SUGARY-1 AND SHRUNKEN-2 LOCI ON KERNEL CARBOHYDRATE CONTENTS, PHOSPHORYLASE AND BRANCHING ENZYME ACTIVITIES DURING MAIZE KERNEL ONTOGENY

The changes in the contents of dry matter, reducing and non-reducing sugar, water-soluble polysaccharide, starch, and the activities of phosphorylase and the branching enzyme were determined during maize kernel ontogeny for the four possible combinations of the su1 and sh2 genes in a common genetic background. The increase in carbohydrate content expressed as percent of the kernel dry matter was greatest during the 12-18-day period following pollination for all genetic lines. By the 15th day after pollination, reducing sugar content was decreasing in all lines. This was also the time of maximum non-reducing sugar content for kernels of the full (Sh2) lines; however, in the shrunken (sh2) lines the non-reducing sugar content was present in large quantities throughout the remainder of the sampling period. Water-soluble polysaccharide occurred to an appreciable extent only in the sugary-full line. The phosphorylase activity of the shrunken kernels was over twice that of the full kernels, suggesting that phosphorylase may be influenced by the sh2 gene. The branching enzyme activity of the sugary-full kernels was much higher during the early sampling dates than those of the other lines and the starch of the sugary-full line consisted almost entirely of amylopectin. © 1970.