Effects of simetryne on the photochemical reactions of isolated chloroplasts of rice and barnyardgrass plants.

Abstract

The effects of simetryne on the photosynthetic electron transport and photophosphorylation activities in chloroplasts isolated from rice (tolerant) and barnyardgrass (susceptible) plants were investigated. Simetryne severely inhibited the electron transport of photosystem II in both the chloroplasts as measured by O2 evolution (pI50 value was 7.3). No inhibition of photosystem I dependent electron transport was observed up to 10-4M simetryne. Non-cyclic photoposphorylation was inhibited by simetryne at the same concentration as in inhibition of photosystem II. Cyclic photophosphorylation was also inhibited, but not as severely as in non-cyclic reaction. The primary herbicidal action of simetryne seems to be inhibition of photosystem II and photophosphorylation. No differences were observed in the degree of inhibition between chloroplasts isolated from rice and barnayrdgrass among all photochemical reactions tested. It cannot therefore be considered that the selectivity of simetryne is caused by the difference in sensitivity of the chloroplasts.