Lipid Mobilization in Dormant and Nondormant Caryopses of Yellow Foxtail (Setaria lutescens)

Abstract

The major reserve lipid of yellow foxtail [Setaria lutescens(Weigel) Hubb.] caryopses is triacylglyceride stored in lipid bodies. Lipid bodies are heavily concentrated in the cells of the embryo axis, scutellum, and aleurone layer and are roughly spherical (average diam 0.5μm). Percentage lipid (hot isopropanol extract) on a fresh-weight basis of mature, unimbibed seed and caryopses collected locally was about 6.4 and 11%, respectively. About 95% of the total (0.23 mg/caryopsis) was saponifiable and distributed among fatty acid classes as follows: 16:0, 5.8%; 18:0, 1.5%; 18:1, 16.2%; 18:2, 73.7%; and 18:3, 2.8%. In nondormant caryopses, saponifiable lipid content declined (18:1 and 18:2 only) about 23% during the first 6 days after imbibition in the dark at 25 C. This modest decline was preceded by the appearance of an alkaline lipase at about 24 h after the onset of imbibition. Free fatty acids accumulated during these early stages of germination and accounted for about 22% of the total saponifiable lipid remaining (0.17 mg/caryopsis) 6 days after the onset of imbibition. Lipid content and lipase activity did not change in dormant caryopses treated similarly. The delayed initiation of lipid mobilization in germinating caryopses suggests that triacylglyceride degradation is not a pivotal metabolic pathway controlling dormancy.