Studies on the modes of action of n-alkylguanidines and triorganotins on photosynthetic energy conservation in the pea and the unicellular alga Chlamydomonas reinhardi Dangeard

Abstract

The pea ( Pisum sativum L.) and the CW 15 (cell wall-less) strain of the unicellular alga Chlamydomonas reinhardi Dangeard were used to investigate the modes of action of two n-alkylguanidines and several triorganotin salts on reactions associated with photosynthetic energy conservation. The two n-alkylguanidines, n-octylguanidine and n-dodecylguanidine, affected state 3 (ADP stimulated) noncyclic electron transport of pea chloroplasts in a concentration-dependent manner, viz, energy transfer inhibition at low concentrations, uncoupling of electron transport from photophosphorylation at intermediate concentrations, and direct inhibition of electron transport at relatively high concentrations. The Ca 2+-dependent ATPase (EC 3.6.1.5) activity of C. reinhardi chloroplast fragments was inhibited by both n-alkylguanidines over concentration ranges similar to those required to affect state 3 electron transport in pea chloroplasts. Dodecylguanidine required lower concentrations than octylguanidine to produce similar effects in both assays. The triorganotins produced uncoupler-reversible inhibition of the state 3 electron transport of pea chloroplasts in a sucrose medium and uncoupled the electron transport in a medium containing high chloride concentrations, as shown by their stimulation of both the light-induced transmission changes and the decay of the light-induced pH gradients of chloroplast suspensions. The inhibition of the Ca 2+-dependent ATPase activity of C. reinhardi by most of the triorganotins was correlated to their inhibition of the growth of the alga on agar medium under different trophic conditions. The efficacies of the tri- n-alkyltins in all the assays used generally increased along the homologous series.