Diurnal Oscillation of Amylolytic Activity in Spinach Chloroplasts

Chloroplasts isolated from spinach (Spinacia oleracea L., cv. vital(R)) plants grown under controlled light/dark and temperature regimes, contained the phosphorolytic and amylolytic pathways for starch breakdown. The latter consists at least of alpha- and beta-amylase and maltase. Only low amylolytic activity was observed in chloroplasts isolated during the light phase. In chloroplasts prepared during the dark phase, this activity was almost twice as high. These diurnal oscillations of the amylolytic activity were maintained when the plants were kept in prolonged darkness or continuous light. The amylolytic system exhibited a sharp pH optimum between 5.8 and 6.0. Phosphorylase activity, when assayed with saturating concentrations of inorganic phosphate, did not show diurnal fluctuations.