Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2006
Publication Date: 3/1/2006
Citation: He, X., Chen, G.Q., Lin, J.T., Mckeon, T.A. 2006. Diacylglycerol acyltransferase activity and triacylglycerol synthesis in germinating castor seed cotyledons. Lipids. Vol. 41, Number 3: 281-285, 2006. Interpretive Summary: In order to find new uses for vegetable oils in surplus, it is essential to develop alternative uses for them. One approach is to biochemically convert the oil to more valuable products. This paper reports the capability of diacylglycerol acyltransferase (RcDGAT) in incorporating ricinoleic acid into castor oil during seed germination. Castor oil is a vegetable oil with numerous industrial applications, including bio-based plastics, lubricants, bio-fuel additives and coatings. Currently, the domestic market consumes 110 million pounds of this strategically important oil, and it is all imported. The elucidation of the function of RcDGAT in the germination process supports development of biochemical means to produce alternative sources of castor oil. Ultimately, this research will result in domestic capability for castor oil production, expanding the availability of bio-based products.
Technical Abstract: The central importance of storage lipid breakdown in providing carbon and energy during seed germination has been demonstrated by the isolation of genes encoding the enzymes involved in fatty acid '-oxidation. In contrast, little is known about the ability of germinating seeds to synthesize triacylglycerol (TG). We report that castor cotyledons are capable of TG synthesis. The rate of incorporation of ricinoleic acid into TG reached a peak at 7 days after imbibition (DAI) (1.14 nmol/h/mg), decreased rapidly after that, but was sustained at 20 DAI in cotyledons and true leaves. By Northern and western blot analyses we found that castor diacylglycerol acyltransferase (RcDGAT) mRNA and protein were expressed throughout seed germination. Significant degradation of the RcDGAT protein was observed after 7 DAI. It was found that the DGAT activity was predominantly a function of the level of the intact RcDGAT protein, with the rate of TG synthesis decreasing as degradation of the RcDGAT protein proceeds. A possible mechanism for the degradation of the RcDGAT protein is discussed.