Inhibition by Sethoxydim of Pigment Accumulation and Fatty Acid Biosynthesis in Chloroplasts of Avena Seedlings

Abstract

The cyclohcxanedionc derivatives sethoxydim and alloxydim block leaf growth and inhibit the accumulation of photosynthetic pigments (chlorophylls, carotenoids) in expanding leaves of oat seedlings, but do not affect the rate of photosynthesis in the primary or secondary leaves. In isolated intact oat chloroplasts the incorporation of [2-14C)acetate into the total fatty acid fraction is strongly inhibited by the two herbicides sethoxydim and alloxydim. The I50 -values for the inhibition of [14C]acetate incorporation into fatty acids are 5 × 10-7 ᴍ for sethoxydim and 2 × 10-6 ᴍ for alloxydim. The desethoxyimino derivative of sethoxydim. M1-S, a degradation product of sethoxydim, does not interfere with the fatty acid biosynthesis of isolated oat chloro­plasts. In isolated chloroplasts of the dicotyledonous plants pea and spinach, which as whole plants are tolerant towards sethoxydim, no significant inhibition of the fatty acid biosynthesis by sethoxydim could be found. It is assumed that the primary mode of action of sethoxydim and alloxydim is in blocking the fatty acid biosynthesis in the sensitive gramineous plants.