PLANT-CELL MEMBRANES AS BIOCHEMICAL TARGETS OF THE PHYTOTOXIN HELMINTHOSPOROL

Helminthosporol is one of the natural sesquiterpenoid toxins isolated and identified in the culture medium of the phytopathogenic ascomycete fungus Cochliobolus sativus. The effect of this phytotoxin was invest igated on enzymatic activities, electron and ion transport in mitochon dria, chloroplasts, and microsomes of plant. The results indicate that helminthosporol drastically affects the membrane permeability of thes e organelles to protons and subtrate anions, inhibiting the mitochondr ial oxidative phosphorylation, the photophosphorylation in chloroplast s, and the proton pumping across the cell plasma membrane. The 1,3-bet a-glucan synthase activity, involved in defense mechanisms of plant ce lls against stress and damage, e.g., during pathogen attack, was also strongly inhibited by the toxin.