Inhibition of photosystem II in spinach chloroplasts by trachyloban-19-oic acid

The effect of trachyloban-19-oic acid isolated from Iostephane heterophylla (Asteraceae), was investigated on several photosynthetic activities in spinach thylakoids. The results indicated that this compound inhibited ATP synthesis and uncoupled electron transport, as well as basal and phosphorylating electron flow. Therefore, trachyloban-19-oic acid acts as Hill reaction inhibitor. This compound did not affect photosystem I activity but inhibited uncoupled photosystem 11 electron flow from H2O to DCPIP, and has not effect on electron flow from H2O to SiMo, indicating that the site of inhibition of this compound is at the level Of Q(A)-Q(B). Chlorophyll a fluorescence measurements confirm the behavior of this diterpene as Q(A)-Q(B) inhibitor, and in the other hand, this results indicate that a perturbation in the thylakoid membranes at the level of LHC II occurs. (C) 2003 Elsevier Science (USA). All rights reserved.