The Physiology of Sugar-Cane VIII. Diurnal Fluctuations in The Activity of Soluble Invertase in Elongating Internodes

Abstract

The activity of acid invertase in the storage compartment of elongating internode cells of sugar-cane stems fluctuates several fold during a single days, reaching a maximum early in the morning and falling to a minimum late in the afternoon. Parallel fluctuations in either protein content or hexokinase activity did not occur. Diurnal fluctuations in invertase activity were observed both in field-grown plants and in plants grown in a controlled environment where the only environmental variable was a light-dark cycle. Exposure to low intensity red or far red light during darkness had no effect on invertase activity. An explanation is presented in terms of the glucose-mediated repression of invertase synthesis, the degree of repression being dependent upon the cytoplasmic glucose concentration which fluctuates as the result of changes in the amount of sucrose in the translocation stream.