Photosystem II and its connection to the electron transport chain during the life cycle of Chlorella

Chlorophyll a fluorescence induction curves in the subsecond time range were recorded through the life cycle of Chlorella . Developmental changes were followed in the maximum quantum yield of photochemistry, in the concentration of the Photosystem II (PS II) reaction centers, in the size of the plastoquinone pool and its connection to PS II, and in the size of the PS II units and their connectivity. In the first 4 h of the cycle, there is a 35% increase in the PS II reaction center concentration (per chlorophyll), a 35% decrease in the size of the PS II units and a 15% increase in the connectivity between them. The connectivity of the PS II reaction centers to the electron transport chain rises during this time. After a period of constancy, at the 10th h the reaction center concentration falls, while the PS II unit size increases. Upon cell division, large, but isolated units, poorly connected to the electron transport chain, are found.