Internal CO2 Supply during Photosynthesis of Sun and Shade Grown CAM Plants in Relation to Photoinhibition

Leaves of Kalanchoë pinnata were exposed in the dark to air (allowing the fixation of CO(2) into malic acid) or 2% O(2), 0% CO(2) (preventing malic acid accumulation). They were then exposed to bright light in the presence or absence of external CO(2) and light dependent inhibition of photosynthetic properties assessed by changes in 77 K fluorescence from photosystem II (PSII), light response curves and quantum yields of O(2) exchange, rates of electron transport from H(2)O through Q(B) (secondary electron acceptor from the PSII reaction center) in isolated thylakoids, and numbers of functional PSII centers in intact leaf discs. Sun leaves of K. pinnata experienced greater photoinhibition when exposed to high light in the absence of CO(2) if malic acid accumulation had been prevented during the previous dark period. Shade leaves experienced a high degree of photoinhibition when exposed to high light regardless of whether malic acid had been allowed to accumulate in the previous dark period or not. Quantum yields were depressed to a greater degree than was 77 K fluorescence from PSII following photoinhibition.