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Effect of Ethrel and Ceratocystis fimbriata on the Synthesis of Fatty Acids and 6-Methoxy Mellein in Carrot Root ^1,2

J. G. Jaworski and J. Ku

^a Department of Biochemistry and of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

The rate of incorporation of ¹⁴C from acetate-1-¹⁴C into fatty acids by carrot root discs, 18 hours after inoculation with Ceratocystis fimbriata, was 9-fold greater than that in freshly cut discs. The rate in discs treated with water or Ethrel was 3-fold greater. The rate of incorporation of ¹⁴C from glucose-U-¹³C into fatty acids was 3-fold greater 18 hours after any of the above treatments. The rate of ¹⁴C incorporation from malonate-2-¹⁴C into fatty acids 24 hours after inoculation with C. fimbriata or treatment with water was 25 and 60%, respectively, of that in freshly cut discs. Linoleic acid was the principal fatty acid in carrot root, but incorporation of ¹⁴C from acetate-1-¹⁴C into the acid was low until 18 hours after inoculation with C. fimbriata or treatment with Ethrel. Turnover rates of the fatty acids appeared low and were similar for all treatments.

There was little or no incorporation of ¹⁴C from acetate or malonate into 3-methyl-6-methoxy-8-hydroxy-3,4-dihydroisocoumarin (6-methoxy mellein) in fresh carrot discs or in discs treated with water, but label was incorporated rapidly in discs inoculated with C. fimbriata or treated with Ethrel. The rate of incorporation of label from acetate into fatty acids was severalfold higher than into 6-methoxy mellein, but the rate of incorporation of label from malonate was approximately equal into fatty acids and 6-methoxy mellein 24 hours after inoculation. The rate of fatty acid synthesis does not appear directly related to the accumulation of 6-methoxy mellein.

² Research supported in part by Grant GB 13994A No. 1 of the National Science Foundation and a National Defense Education Act fellowship.