Variation of fatty acid composition in different tissues during Astragalus membranaceus seedling morphogenesis

Morphogenesis is a critical stage for the successful seedling establishment, which relies on energy provided by seed storage. Lipids are utilized as the primary energy storage material in most seed plants. The significance of alterations in fatty acid composition for seed germination has been reported; however, the mechanism underlying fatty acid utilization during morphogenesis remains unclear. Thus, the variation of fatty acid composition in response to light and dark signals was investigated in different tissues during Astragalus membranaceus seedling morphogenesis. Major difference in cotyledon was observed in fully opened and expanded. Compared to dark, light induced α-C18:3, C14:0 and C16:1 increased by 28%, 54%, and 86%, and C18:1, C21:0 and C20:0 decreased by 38%, 35%, and 11%, respectively. It seemed that the weakening of very long-chain fatty acids elongation and the enhancement of the palmitic acid elongation pathway, may have contributed to the synthesis of polyunsaturated fatty acids. Moreover, the changes of α-C18:3 in plastid membrane were significantly related to that of cotyledons. In newly differentiated tissues, the proportion of C16:0 and C18:0 in dark continued to increase to 36% and 20% while α-C18:3 gradually decreased to 15%, respectively. However, the increase or decrease in light were both stopped on A3 in which its elongation was inhibited. Meanwhile, it contained higher level of C22:0 in light and C22:1 in dark. Beyond that, C20:0, C16:1 C21:0 and C23:0 in both light and dark remained unchanged before cotyledon unearthing, then markedly increased after unearthing. Thus, our results presented a novel pattern of variation of fatty acid composition, which was important for understanding seedling morphogenesis.