Sucrose Accumulation and Key Enzyme Activities in Different Parts of Seed in Vegetable Soybean

Abstract

Three vegetable soybean varieties(lines)with different soluble sugar contents were grown in field condition.Sucrose contents and four critical enzymes activities in different parts of seed were analyzed at R5.5,R6,R6.2,R6.5,and R7 stages,respectively.Sucrose contents of different seed parts increased at early seed filling stage and then decreased at late stage with the peak value at R6.2 stage.Sucrose content in hypocotyl was 57.6%,53.6%,44.2% greater than that of cotyledon,and 71.6%,75.3%,73.6% greater than that of seed coat at R6.2 stage for the three varieties(lines),respectively.The cotyledon contributed90% dry weight to the total seed dry weight,and thus the sucrose content of the whole seed was primarily determined by sucrose content in cotyledon.Cotyledon had the highest activity of sucrose phosphate synthase(SPS).The cotyledon SPS activity of cv.121 was much higher than those of the other two varieties(lines).The sucrose synthase(SS)activity of different seed parts was higher in early seed filling stage than in late filling stage.The highest value of SS activity was observed in hypocotyl at R5.5 stage.Greater differences were found between acid invertase(AI)and neutral invertase(NI)activities.NI activity was higher in early seed filling stage and then decreased till R7 stage.Significant differences were observed for AI activities among three seed parts at the same seed filling stage but there were no differences for NI activities.AI activity in seed coat was much higher than those in hypocotyl and cotyledon.Negative relationship was found between AI activity and sucrose content in seed coat(r = –0.59**).The correlation analysis between sucrose accumulation and four critical enzymes activities showed that seed sucrose content was not controlled dominantly by one enzyme.The difference between sucrose synthesis enzyme activity(SPS)and sucrose decomposition enzyme activity(SS+AI+NI)was positively correlated with seed sucrose accumulation(r=0.53**).