CHANGES IN FATTY-ACID COMPOSITION AND STEAROYL-ACYL CARRIER PROTEIN DESATURASE EXPRESSION IN DEVELOPING THEOBROMA-CACAO L EMBRYOS

The fatty-acid composition and expression of stearoyl-acyl carrier pro tein (ACP) desaturase (EC 1.14.99.6) were studied in developing Theobr oma cacao L. embryos between 95 and 145 days after pollination (DAP). During this interval, the fraction of lipid contributed by linoleic an d palmitic acids decreased, and the fraction contributed by stearic an d oleic acids increased. After 115 DAP, stearic, palmitic, and oleic a cids accumulated at nearly the same rate, and the fatty-acid compositi on resembled that of cocoa butter. The ratio of C-18 unsaturated fatty acids to stearic acid decreased between 95 and 115 DAP, then leveled- off. Thus, lipid composition changed from membrane-like to cocoa-butte r-like in only 20 d out of the 170 d required for embryos to reach mat urity. Levels of stearoyl-ACP desaturase were determined by Western bl ot analyses using antibodies to avocado stearoyl-ACP desaturase. Weste rn blots revealed a single 38-kDa band - corresponding to the expected size of the stearoyl-ACP-desaturase monomer - in extracts from 95- an d 105-DAP embryos. Although the amount of stearoyl-ACP-desaturase prot ein was 2.3-fold higher at 95 than at 105 DAP when equal amounts of pr otein were loaded per lane, no difference in the abundance of stearoyl -ACP desaturase was observed when the protein loaded per lane was stan dardized for equal amounts of DNA.