SUCROSE METABOLISM IN SUGARCANE CELL-SUSPENSION CULTURES

Enzymes of sucrose metabolism in sugarcane cell suspension cultures were followed throughout a cell culture cycle (14 days) to monitor relative changes in the activities of enzymes directly involved in sucrose synthesis and hydrolysis. Doubling of initial sucrose-phosphate synthase (SPS) activity corresponded to the time when the sucrose accumulation rate had reached its peak. Sucrose synthase (SS), measured in the direction of synthesis, reached a high rate of activity during the period of maximal sucrose increase. Activity of SS in the direction of sucrose hydrolysis was much lower and decreased throughout the cell culture cycle. Invertase, measured at pH 7.0, followed a similar pattern to that for sucrose hydrolysis by SS. Acid invertase, assayed at pH 5.5, exhibited a high rate of activity at the beginning of the culture cycle and was followed by a sharp decline during sucrose accumulation. The rate of maximal sucrose accumulation was determined to be approximately 167 nmol h-1 (g fresh wt.)-1. The average activity of SPS during the same period was 8970 nmol h-1 (g fresh wt.)-1. Therefore, all sucrose synthesis in the cell cultures can be ascribed to SPS activity, whereas SS most likely functions in a degradative capacity.