Derivatives of diterpen labdane-8α,15-diol as photosynthetic inhibitors in spinach chloroplasts and growth plant inhibitors

Abstract In a search of new efficient herbicides of natural origin, four derivatives were prepared from labdane-8α,15-diol ( 1) and 15-O-acetyl-8α-hydroxy labdane ( 2 ) isolated from Croton ciliatoglanduliferus . Their inhibitory activity on photosynthetic electron transport on fresh, broken spinach chloroplasts and on the growth of plants were determined. Derivative 15-O-benzoyl-8α-hydroxy labdane ( 5 ) was seven times more active than 2 as reaction Hill inhibitor. Complex of 5 with the adjuvant 2-hydroxypropyl-β-cyclodextrin ( 5:HPB ) (200 μM) was sprayed on Physalys ixocarpa (green tomato) plants; 48 h later the complex inhibited PS II by transforming the active reaction centers to silent reaction centers or “heat sinks”. After 72 h this effect disappeared, probably 5:HPB was metabolized by the plant. Chlorophyll a fluorescence of Trifolium alexandrinum (clover) leaves was affected with 5:HPB at the level of PQ pool reduction. 5:HPB decreases the tomato and clover dry-biomass, without affecting Lolium perenne (grass) plants, suggesting that complex 5 acts as selective herbicide for dicotyledonous plants.