Fatty Acids Accumulation In Mature Seeds And Utilization In Germinating Seeds Of Suaeda Salsa

Soil salinization has become the bottleneck of agricultural development with the growth of people's demand for food.Suaeda salsa is a euhalophytic herb,which produces bigger brown seeds and smaller black seeds.Seed oil of S.salsa is edible and rich in unsaturated fatty acids.However,the mechanism for the accumulation of fatty acids in dimorphic seeds of S.salsa is not clear.Therefore,the characteristics of seed oil and fatty acids accumulation,and the effect of salinity on utilization of stored lipids during germination in dimorphic seeds of S.salsa were studied.The results are as follows: 1.Analysis of seed oil content and fatty acid composition in field conditionMature seeds of S.salsa in inland saline soils were collected from the Yellow River Delta of Shandong province.After naturally drying,black seeds and brown seeds were distinguished.Seed oil extraction was carried out by Soxhlet extraction,and the fatty acid components were analyzed by gas chromatography.The results showed that the content of seed oil in black and brown seeds was about 19%,and there was no obvious difference between dimorphic seeds.The composition of fatty acids in black and brown seeds was consistent,and the content of unsaturated fatty acids was rich,i.e.,the proportion of polyunsaturated fatty acids was more than 76%.The highest composition of fatty acids were linoleic acid(C18: 2)(> 70%),followed by oleic acid(C18: 1),palmitic acid(C16: 0)and ?-linolenic acid(C18: 3).Black seeds had more unsaturated fatty acids,and the unsaturated/saturated ratio and polyunsaturated/saturated ratio for fatty acids were higher in black seeds than brown seeds.In addition,the quantitative PCR results showed that the expression of Ss FAD7 in brown seeds was much higher than black seeds.This may be related to higher content of ?-linolenic acid in brown seeds than black seeds.2.Effect of salinity on seed oil content and fatty acid compositions in controlled conditionThe effect of salinity on lipid content and fatty acid compositions in dimorphic seeds of S.salsa grown under controlled condition was carried out.Salinity increased the total seed oil content in black and brown seeds,i.e.,the value at 200 m M Na Cl was 1.95 and 1.88 times of that at 0 m M Na Cl for black and brown seeds,respectively.However,there was no difference in the total seed oil content between brown and black seeds at the same concentration of Na Cl.Salinity increased the content of unsaturated fatty acids.The content of linoleic acid and oleic acid in black seeds was higher than brown seeds,but the opposite trend was shown in ?-linolenic acid at each concentration of Na Cl.The enzyme activity of ?-3 FAD in brown seeds was much higher than that in black seeds,but salinity had no significant effect on that in both brown and black seeds.It seems that salinity increased the content of ?-linolenic acid more obviously in brown seeds than black seeds.This was confirmed by quantitative PCR results,i.e.,salinity significantly increased the expression of Ss FAD7 in both black and brown seeds,especially in brown seeds.3.Utilization of stored lipids during germination in dimorphic seedsUtilization of stored lipids plays an important role in germination of oil seeds.In the present study,key enzyme activity(lipase,isocitrate lyase and malate synthase)in lipid utilization was determined during germination in dimorphic seeds of S.salsa.The results showed that the percentage of germination were highest in intertidal brown seeds,followed by inland brown seeds and then inland black seeds moistened with 0 and 300 m M Na Cl during early seed germination.The same trend was found in the activity of three enzymes and soluble sugar content when seeds were moistened with 0 and 300 m M Na Cl for 3 h.Salinity reduced the activity of three enzymes in inland brown and black seeds in the initial 3 h,except that salinity had no adverse effect on isocitrate lyase activity of brown seeds.Salinity had no adverse effect on three enzymes in inland brown and black seeds in the initial 30 h,except that salinity decreased malate synthase activity of black seeds.Salinity had no effect on three enzymes in intertidal brown seeds in the initial 3 h and 30 h.In conclusion,high activity of these enzymes in brown seeds may play an important role in utilization of stored lipids during their rapid seed germination.