Phototropism of Pellia: Evidence for Mediation by Auxin-stimulated Acid Efflux

Flash induced 685 nm fluorescence emission of preilluminated and dark kept Chlamydobotrys stellata has been measured under conditions of CO₂-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. CO₂ removal from growing cultures of this alga for 15 min diminishes photosynthetic electron transport at the oxidizing side of this photosystem. Prolonged CO₂-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.