Diurnal Variations in Some Enzymes of Carbohydrate Metabolism in Tapioca Leaves

Although diurnal rhythmicity in the overall metabolic activity of plants and lower organisms has been recognized (2,8), there have been only a few studies of any possible associated rhythmicity at the enzymatic level. Diurnal variations in oxidase and catalase in the tobacco plant (23), in amylase and phosphatase in Phaseoluts mwltiflorus and Kalanchoe blossfeldiara (4, 5), and in amylase in Spinacea oleracia and Perilla ocymoides (25) have been reported. One of the most convincing evidences showing that physiological rhythm is a reflection of biochemical alterations relates to the luminescence in Gonyaulax, where luciferin and luciferase are found in greater amounts in cell-free extracts prepared during the dark period (9, 21). Members of this laboratory have been engaged in investigations aimed at elucidating rhythmicity, if any, in the level of plant enzymes and their substrates. Sanwal and Krishnan (15) observed that aldolase and phosphatase of cactus showed distinct diurnal variations and the authors put forward a hypothesis to explain the significance of the alterations in the activities of these two enzymes. This was followed by a report by Mukerji et al. (12) that transaminase displayed a marked diurnal variation in cactus. The activity in the evening was several-fold that of samples collected at night and early morning, when the titratable acidity was maximum. The conclusions of these authors are subject to the criticism that homogenates were prepared in water and, as such, the marked changes in the acidity of the different homogenates may have resulted in inactivation of transaminase to a different extent, yielding values for activity which are artifacts. Sufficiently sensitive methods are not available to determine the influence, if any, of vacuolar acids on the pH of protoplasm in vivo in the succulent plants. It was also observed in this laboratory that cactus tissue showed a significant diurnal variation in protein and in nonprotein nitrogen content; the former increased and the latter decreased in the day time; the levels were restored at night. It was of interest to examine whether or not such diurnal variations are exhibited also by nonsucculent tissues, which do not possess