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.

Triacylglycerol Metabolization during Germination of Sea Buckthorn Seeds

“…Earlier, similar results were obtained in the experiments with cotton, hazel, and yellow foxtail seeds, in which this value increased 3-8-fold during germination [16,22,23]. At the same time, a dry weight decrease, caused by reserve consumption during the sea buckthorn seedling growth, proceeded steadily, but at a slow rate.…”

“…At the same time, a dry weight decrease, caused by reserve consumption during the sea buckthorn seedling growth, proceeded steadily, but at a slow rate. A slow mobilization of cotyledon reserves was also observed in the experiments with linseed [12], hazel [16], tobacco [24], yellow foxtail [23], and two cruciferous species [11]; however, in corn [25], cotton [22], nut pine [9], and water melon [26] seeds, their dry weight contents decreased two-or even threefold by the end of germination. The causes for differences between various plant species in this respect are still unknown at present.…”

“…On the one hand, they involve delays in the biosynthesis or activation of the enzymes of this process, primarily lipase; in the transport of these enzymes into oleosomes; or in the formation of organelles, such as glyoxysomes, mitochondria, etc., which are essential for TAG and FA degradation. On the other hand, they involve a temporary inhibition of FA breakdown under the action of excess soluble carbohydrates in the cotyledon tissues [14,23,32].…”

“…It is of interest that, along with sea buckthorn, a lagperiod of TAG utilization was observed up to now almost exclusively in the seedlings of non-oleiferous plant species, such as maize [25], euphorbia [30], borage [10], manihot [33], nut pine [9], hazel [28], tobacco [24], yellow foxtail [23], etc. At the same time, this phase was absent in many major industrial oil crops, such as sunflower [34], soybean [13,17], linseed [12], rapeseed [18,31], castor bean [28], and cotton [35].…”

Effects of low-oxygen atmospheres on impatiens seed germination

“…One gram of sea sand was ground with the seed to absorb the oil. The lipid content was estimated by using a modification of the procedure described by Lehle et al, 1983. The ground sea sand-impatiens mixture was distilled in a microsoxhlet apparatus with 10 ml isopropyl alcohol for 2 hours.…”