Changes in the Enzymes for Fatty Acid Synthesis and Desaturation during Acclimation of Developing Soybean Seeds to Altered Growth Temperature.

Temperature-induced changes in the enzymes for fatty acid synthesis and desaturation were studied in developing soybean seeds (Glycine max L. var Williams 82). Changes were induced by culture of the seed pods for 20 hours in liquid media at 20, 25, or 35 degrees C. Linoleoyl and oleoyl desaturases were 94 and 10 times as active, respectively, in seeds cultured at 20 degrees C as those cultured at 25 degrees C. Both desaturases had negligible activity in seeds cultured at 35 degrees C compared to seeds cultured at 20 degrees C. Though less dramatic, other enzymes also showed differences in activity after 20 hours in culture at 20, 25, or 35 degrees C. Stearoyl-acyl carrier protein (ACP) desaturase and CDP-choline:diacylglycerol phosphorylcholine transferase were most active in preparations from 20 degrees C cultures. Activities were twofold lower at 25 degrees C and a further threefold lower in 35 degrees C cultures. Cultures from 25 and 35 degrees C had 60 and 40%, respectively, of the phosphorylcholine:CTP cytidylyl transferase activity present in cultures grown at 20 degrees C. Fatty acid synthetase, malonyl-coenzyme A:ACP transacylase, palmitoyl-ACP elongation, and choline kinase were not significantly altered by culture temperature. These data suggest that the enzymes for fatty acid desaturation and phosphatidylcholine synthesis can be rapidly modulated in response to altered growth temperatures, while the enzymes for fatty acid synthesis and elongation are not.