Influence of metolachlor and the metolachlor protectant CGA 43089 on the biosynthesis of epicuticular waxes on the primary leaves of Sorghum bicolor Moench

Epicuticular wax synthesis by the primary leaf of Sorghum bicolor seedlings is inhibited when the germinating seeds are treated with 5 ppm metolachlor before germination. The composition of the free and esterified primary alcohols plus free and esterified fatty acids and aldehydes have been analysed. The predominant alcohol (75%) had 32 carbons while the 28- and 30-carbon homologues accounted for 78% of the fatty acids. Treatment of the germinating seeds with metolachlor strongly inhibited formation of the C₂₈, C₃₀ and C₃₂ alcohols. Synthesis of C₃₀ and C₃₂ fatty acids was decreased while that of the C₂₆ homologues was somewhat elevated. Simultaneous treatment of the germinating seed with metolachlor and the herbicide protectant CGA 43089 (α-[cyanomethoximino]-benzacetonitrile) resulted in normal wax synthesis. The results lead to the conclusion that the protectant prevents metolachlor from inhibiting synthesis of the dominating C₂₈ to C₃₀ chain-length constituents of the sorghum epicuticular wax.