STUDIES ON THE EFFECT OF DIFFERENT CYCLOHEXANE-1,3-DIONES ON DE-NOVO FATTY-ACID BIOSYNTHESIS IN POACEAE

Cyclohexane-1,3-diones such as the herbicides cycloxydim, sethoxydim, alloxydim and clethodim are known to be specific inhibitors of the pla stid-located acetyl-CoA carboxylase (ACCase) in Poaceae, a key enzyme of de-novo fatty acid biosynthesis in higher plants. Using several new cyclohexane-1,3-dione derivatives and known herbicides, the relations hips between chemical structure and enzyme inhibition have been studie d. The basic cyclohexane-1,3-dione structure was modified at three dif ferent positions. These compounds were tested for inhibition of the de novo fatty-acid biosynthesis in test systems of etioplasts isolated f rom Avena sativa L. and Hordeum vulgare L. seedlings and also for inhi bition of the isolated barley ACCase. The I-50 values of these cyclohe xane-1,3-diones were determined. The influence of the modification of alkyl chains (length and type of substituent) on the degree of ACCase- inhibition is discussed. Several new compounds were found that were ab out two orders more active than the known herbicides cycloxydim or set hoxydim in the etioplast and ACCase test systems but not necessarily o n the level of whole plants.