AbstractThe possible relationship between folate levels in plants and their tolerance to asulam has been examined. Plants with a high content of folates were relatively less susceptible to asulam. There was evidence of a depletion of the folates in the shoots of plants treated with asulam, either alone at 1. 1 kg ha−1or in combination with 4, 6‐diamino‐1‐(3, 4‐dichlorophenyl)‐1, 2‐dihydro‐2, 2‐dimethyl‐1, 3, 5‐triazine (DCDT) at 1.1 kg ha−1.In wheat shoot tips (Triricum estivumL.), asulam at 1.1 kg ha−1reduced the levels of theN5‐methyl,N10‐formyl andN5‐formyl derivatives of 5, 6, 7, 8‐tetrahydrofolates, particularly when applied in combination with DCDT. Studies with cell‐free extracts of wheat seedlings revealed that asulam inhibited the enzymic synthesis of 7, 8‐dihydro‐pteroateina manner similar to sulphanilamide inhibition. The biochemical site of
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