Bicarbonate in vivo Requirement of Photosystem II in the Green Alga Chlamydobotrys stellata.

Flash induced 685 nm fluorescence emission of preilluminated and dark kept Chlamydobotrys stellata has been measured under conditions of CO(2)-deprivation. The difference in fluorescence intensity between dark kept and preilluminated cells is taken as a measure for the reduced state of the primary stable electron acceptor of photosystem II, Q, at the given intensity of preillumination. CO(2) removal from growing cultures of this alga for 15 min diminishes photosynthetic electron transport at the oxidizing side of this photosystem. Prolonged CO(2)-absence influences also its reducing side. Measurements of flash induced oxygen yields support the conclusion that both sides of photosystem II are affected in the absence of bicarbonate.