Inhibiton of fatty acid biosynthesis in isolated chloroplasts by cycloxydim and other cyclohexane‐1,3‐diones

Abstract

Kobek, K., Focke, M., Lichtenthaler, H.K., Retzlaff, G. and Würzer, B. 1988. Inhibiton of fatty acid biosynthesis in isolated chloroplasts by cycloxydim and other cyclohexane‐1,3‐diones. ‐ Physiol. Plant. 72: 492–498.The effect of the three cyclohexane‐1,3‐dione herbicides cycloxydim, sethoxydim and clethodim (proposed common name) on the de novo fatty acid biosynthesis of isolated chloroplasts as test system was investigated with intact chloroplasts isolated from sensitive grasses (Poaceae) and tolerant dicotyledonous plants. All three herbicides blocked the de novo fatty acid biosynthesis ([14C]‐acetatc incorporation into total fatty acid fraction) in Avena sativa L. cv. Flämingnova chloroplasts in a dose‐dependent manner. The I50‐values are lower for cycloxydim and clethodim than for sethoxydim. The rate of de novo fatty acid biosynthesis in isolated, intact and photosynthetically active Avena chloroplasts was higher in the light than in the dark, which appeared to be due to the light‐dependent regeneration of the cofactors ATP and NADPH. The de novo fatty acid biosynthesis by isolated chloroplasts from the tolerant dicotyledonous species pea (Pisum savivum L. cv. Kleine Rheinländerin), spinach (Spinacea oleracea L. cv. Matador) and tobacco (Nicotiana tabacum L. cv. su/su) was insensitive to the three herbicides. It is assumed that one of the enzymes of the fatty acid biosynthesis is modified in the dicotyledonous plants and not accessible to the cyclohexane‐1,3‐dione herbicides. In the case of Poa annua L., which as a whole plant is tolerant towards sethoxydim, the tolerance seems not to lie in the chloroplasts but in properties of the cytoplasm, since the isolated chloroplasts are sensitive to the herbicide.