Turkish Journal of Botany

Photoinhibition of Cyclic Photophosphorylation and Light-Induced pH Changes in Isolated Spinach Chloroplasts




As a result of comparative investigations of the photoinhibition dynamics of cyclic photophosphorilation CPP) and light-induced pH changes of isolated spinach chloroplasts at room- and low temperature (+1¼C) it was established that the extent and rate of these photoinhibition processes are dependent on temperature. The light-induced pH-change characteristics are inhibited completely during illumination with strong light (100000 1x) at low temperature and room temperature for 30 min. CPP is more sensitive to strong light effects, complete inhibition is obtained in 20 min at low temperature and in 10 min at room temperature. The light-induced pH changes are only inhibited by 50%. The inhibition kinetics of cyclic photophosphorylation in anaerobic and aerobic conditions point out that the acceptor side of Photosystem I is probably involved in photodamage. The results suggest that betaine stabilizes the cyclic photophosphorylation with spinach chloroplasts under the light treatment.


photoinhibition, photosystem I, pH changes, cyclic photophosphorylation, coupling factor.

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