Floridean starch metabolism of Porphyridium purpureum (Rhodophyta)

Abstract

When cells of Porphyridium purpureum are incubated in the dark, the activity of ADPG transferase becomes negligible within 2 days, followed by that of amylase within 4 days and phosphorylase within 6 days. However, there is still a considerable amount of starch within these cells. In contrast, there is an increase in amylase activity in the conchocelis stage of Porphyra leucosticta during 2 days of dark incubation, resulting in complete assimilation of the starch. When partially destarched cells of P. purpureum are transferred from the dark to the light, cycloheximide treatment results in a greater starch accumulation than in control cells whereas there is no increase in starch in cells incubated in chloramphenicol and rifampicin. A 2-day application of cycloheximide eliminates most phosphorylase activity but has little effect on the activity of ADPG transferase. During this period, cycloheximide treatment results in complete cessation of detectable protein synthesis. Incubation of the cells in chloramphenicol decreases the activity of ADPG transferase by about 30% but does not affect phosphorylase. Thus with cycloheximide application, during which phosphorylase activity is eliminated and transferase is fully active, cells accumulate large amounts of starch, indicating that transferase may be the controlling enzyme involved in floridean starch synthesis in P. purpureum. Similar results were found for the chantransia stage of Butrachospermum moniliforme.