Lipid Metabolism in Soybean Seeds during Drought Stress.

Soybean (Glycine max (L.) Merr.) seeds are widely used in food industry due of their high protein and lipid contents being a crucial crop for oil production and raw material for biodiesel. However, climate changes such as drought, one of the most critical environmental stress factors, may alter seed storage compounds. In order to understand the lipid metabolism of seeds under water deficit, a Japanese cultivar ‘Fukuyutaka’ soybean seeds are sown in 1/5000a Wagner pots cultivated in the Kyushu University field until R5 developing stage and transferred to the greenhouse for drought treatment application according to the 50% pot weight of water held.  Since oil content in seed during drought stress was significantly decreased from 19 days after treatment (DAT) as compared with that in control seeds, we analyzed the expression of lipid metabolism related genes. Expression of GmPK, GmBCCP2 and GmKAS1, that participate in fatty acid and triacylglycerol biosynthesis, were decreased during water deficit, while the lipid degradation genes; GmKAT1, GmACX-likes, GmMS and GmICL; showed higher levels. To clarify how lipid metabolism in seed can be regulating in drought stress, the phytohormone abscisic acid (ABA) contents, known to involve in plant stress, and ABA signaling genes expression in seeds under drought stress were investigated.  Besides drought led to significantly increasing of ABA content only at 19 DAT, in absolute values, ABA content in seeds during drought treatment also showed higher than that in control seed. Additionally, the expressions of GmABI-likes genes, that play a role in ABA signaling, were increased by water deficit. Based on these results, lipid metabolism may be regulated by ABA during drought stress. Therefore, more investigation is necessary since it is still unclear how ABA and lipid related genes can affect the seed storage compounds of soybean during seed development under environmental stresses.

Keywords: Abscisic acid (ABA), drought, lipid degradation, soybean seed.