Floridean starch metabolism of Porphyridium purpureum (Rhodophyta). II. Changes during the cell cycle

Abstract

Exponential phase-cells of P. purpureum initiated cell division within the last 2 h of the light period in a 12:12 h photoregime. Cell concentration increased by a factor of 2.5 over 6 h. Starch/ml culture, i.e., regardless of cell division, increased linearly throughout the light phase but declined slightly during the subsequent dark period. Cellular starch contents also rose during the light phase until the beginning of cell division, after which levels decreased to those present at the commencement of the cell cycle. The activities/ml culture of 2 potential starch forming enzymes, phosphorylase and ADPG [adenosine-S-diphosphate glucose] transferase, increased during the light period by a factor of 2.5 to 3.0, thereby keeping pace with the rate of cell division. During the following dark phase, phosphorylase activity remained constant whereas that of transferase declined slightly. Cellular activities of these 2 enzymes rose during the light period until the initiation of cell division and then decreased to levels present at the onset of the light phase. Amylase activity fluctuations were quite different from those of the above enzymes. Levels/ml culture declined at the start of the light phase and did not increase until the last 2 h of that phase. Hence cellular activities remained fairly constant throughout the cell cycle. During the declining growth stage at the end of the exponential phase, cell division was less synchronous and there was active accumulation of starch.