Changes During Early Soybean Seed and Axes Deterioration: II. Lipids

Peroxidative changes in seed lipids are thought to be a major cause of seed deterioration during storage. This study was conducted to determine the fatty‐acid composition of soybean [ Glycine max (L.) Merr.] seeds, axes, and mitochondria during the early stages of deterioration. High‐quality seed lots of ‘Union’ and ‘Desoto’ soybean were stored at 25 °C and 115 g kg ‐ 1 seed moisture for 10 and 12 months, respectively. Seeds were sampled at frequent intervals and the fatty‐acid composition of storage and membrane lipids from seeds, axes, and mitochondria were determined. There were no detectable changes in the fatty‐acid composition of storage lipids from whole seeds or axes during the storage period for either seed lot, despite the substantial decline in seed vigor. There was a slight decrease in the percentage of unsaturated fatty acids in the membrane lipids of excised axes from Desoto seeds. The percentage of unsaturated fatty acids in the mitochondria from excised axes declined early during storage. The double‐bond index (DBI) of lipids from mitochondria of the Union axes fell from 1.76 at the beginning of storage to 1.60 after 10 months. Similar declines of 1.79 to 1.70 after 1 yr in storage were seen for the Desoto axes. Mitochondria! respiration and DBI were highly correlated for both seed lots. These data suggest that the decreases in mitochondrial respiration during storage may be associated with peroxidative changes in mitochondrial lipids and that these changes occurred prior to loss in seed vigor.