Effects of Piperine on Photosynthetic Electron Transport and on Vegetal Growth

Potential herbicide effects of piperine (1) isolated from Piper nigrum (Piperaceae) were investigated on several photosynthetic activities in spinach chloroplasts, in germination, and in growth of roots and stems of seedlings of two monocotyledon species (Triticum aestivium and Echinochloa crus-galli) and two dicotyledonous species (Lactuca sativa and Physalis ixocarpa). The results indicated that this compound inhibited ATP synthesis (I₅₀ of 36.5µM) and accelerates basal and phosphorylating electron flow, however inhibits decoupled electron flow. Therefore, piperine acts as a Hill reaction inhibitor with target of action at the donor electron side of photosystem II and also acts as an uncoupler agent. Piperine inhibited growth of roots and stems of all plantules tested, being more active in L. sativa and the less in E. crusgalli. Germination of seeds was not affected by piperine, with the exception of wheat which was inhibited 28% at 150µM. As respiration of all tested seeds increases in presence of piperine, inhibition of growth of roots and stems could be a result of an uncoupler effect by this compound, similar to that observed in chloroplasts. All mentioned experiments and its results are presented.