In an endeavor to accomplish optimal weed control, with a minimum of ecological damage, numerous QSAR studies have been performed for herbicides inhibiting photosynthetic electron transport in chloroplasts (the Hill reaction). There is no such study dealing with plant-protecting agents (e.g. insecticides) which are not intended to target the plant itself. However, in case of inadequate application, even these compounds can exert phytotoxicity. The main objective of this work was to explore in quantitative terms, the interactions of some nonspecific inhibitors of the Hill reaction with isolated chloroplasts. The study encompassed organophosphorus insecticides (which are widely used in agriculture), chlorinated benzenes (important industrial pollutants), n-aliphatic acids (which accumulate in the plants exposed to stress) and n-aliphatic alcohols. Highly significant correlations (as a rule, r > 0.95) between pI20 (the negative logarithm of the concentration causing 20% inhibition of the Hill reaction) and log P (the logarithm of the partition coefficient in the n-octanol/water system) were established for each of the above mentioned groups of compounds. From the obtained regression models, it may be concluded that all four groups of compounds inhibit the Hill reaction by a similar nonspecific mechanism. On the other hand, their inhibitory potencies were somewhat different and increased in the following order: aliphatic acids < aliphatic alcohols < chlorinated benzenes < organophosphorus insecticides. A model comprising all analyzed compounds could be constructed by introducing indicator variables (I = 1 for a particular group of compounds and zero for the others). We also generated, for the more active compounds, a combined model based on pI50 values (negative logarithm of the concentrations which inhibit the Hill reaction by 50%) which facilitated comparisons with published QSAR models for specific inhibitors of the Hill reaction.

Biologija,Kemija