Molecular And Physiological Mechanisms Of Lipid Metabolism In Camellia Oleifera Seeds During Maturation

Camellia oleifera Abel.is one of important trees for producing edible oil containing more than 80%unsaturated fatty acid in south China.The seeds of C.oleifera were harvested on Oct.25th(P1),Nov.8th(P2)and Nov.22nd(P3)both in 2015 and 2016 as experimental materials.And water content,oil content,acid value and composition of fatty acids in seeds were measured.Label-free proteomic technique was used for analyzing proteome of seeds from year 2015 together with the determination of enzyme activities of 6-phosphofructokinase(PFK),pyruvate kinase(PK),pyruvate decarboxylase(PDC),acetyly-CoA carboxylase(ACCase),lipase(LPS)and lipoxygenase(LOX).The purpose of the present study was to systematically analyze the lipid metabolism molecular and physiological mechanism of C.oleifera seeds during maturation.1.In 2015,the water content of P1,P2 and P3 were lower than P1,P2 and P3 in 2016,respectively,and the oil contents were contrary.Because the frost happened in the early of 2016 have done harm to the C.oleifera tree,the maturation of seeds was affected resulting in high water content and low oil content in 2016.But there is no significant difference between acid values of these samples in both two years.In addition,the changes of composition of fatty acid had a similar trend in 2015 and 2016.These results indicated that fatty acid metabolism in C.oleifera seeds could be a conservative physiological metabolic process during maturation,and it could be relevant to the characteristic of composition of fatty acids in C.oleifera seeds.2.The results of comprehensive proteomic analysis using label-free in C.oleifera seeds showed that,there were 27 proteins relevant to carbohydrate and energy metabolism showing complex regulation,and 10 proteins relevant to lipid metabolism which mainly shows down-regulation.The results of determination of enzyme activity showed no significant changes of the activities of PFK and PDC in the seeds during maturation,decrement of the activities of PK,ACCase and LPS in P3 compared to P1,and increase of the activity of LOX in P2 compared to P1 and P3.These results indicated that,the accumulation of triacylglyceride(TAG)was due to the activation of carbohydrate degradation,fatty acid synthesis and lipid degradation.And the slow-down of the accumulation of TAG might be owing to the down-regulation of these metabolism pathways.Due to the decrease of the branch of glycolysis at P3,the energy and substrates for TAG synthesis in C.oleifera seeds were accumulated.Based on the down-regulated abundant of long chain acyl-coenzyme synthase(LCAS)and the up-regulated activity of LOX,the relative contents of linoleic acid in seeds at P2 were significantly decreased compared to other samples.Owing to the substrate selectivity of LOX,this mechanism could be an important way for controlling relative content of linoleic acid and linolenic acid,activated once polyunsaturated fatty acids in seeds were excessive and made the linoleic acid and linolenic acid oxidated and degraded to guarantee the seed oil’s characteristics of high content of oleic acid and excellent composition of fatty acids.In conclusion,these findings provide new opinions for the research of molecular and physiological mechanism of lipid metabolism in C.oleifera seeds,and lay a foundation for the research in the future.