Mechamsm On Formation Of Distinctive Seedcoat Features In Yellow-Seeded Rape(Brassoca Napus L.)

Yellow seeds in Brassica species are characterized with thinner seedcoat and lower hull percentage which in turn are correlated with higher oil and protein and lower crude fiber contents compared to black seeds under the same genetic conditions. But the widespread application of yellow-seeded species in Brassica napus L. is limited seriously owing to it's genetic instability.Therefore,the search of the mechanism on the formation of distinctive seedcoat features is meaningful for both rapeseed breeding and plant genetics.Many studies were on the pigments in the seedcoatUp to now, rare researches were reported of the reason on the lower hull percentage in yellow-seeded rape.Three pairs of different genetic near-isogenic lines of black- and yellow-seeded Brassica napus as experimental materials were used in my study. The results are as follows:1 .The changes in pigments in seedcoat were investigated with the development of rape seed.The results of experiments and variance analysis showed that there was no significant difference in pigments contents among the three pairs of materials.Butjthe contents of chlorophyll,polyphenols,anthocyanin and melanin in seedcoat were different between black- and yellow-seeded lines and the differences were up to highly significant level. The results showed that chlorophyll content in yellow-seeded lines was much higher than that in black ones when seeds are nearing mature.The contents of polyphenols,anthocyanin and melanin in seedcoat of black-seeded lines were significantly higher than those of yellow-seeded ones.The contents of polyphenols and anthocyanin declined and the content of melanin increased rapidly in the late stage of seed development. So it was speculated that polyphenols and anthocyanin contents might influence the colour of seedcoat,but melanin content might be the mam factor to influence the colour of seedcoat.2.The indexes related to thickness of seedcoat were measured with the seedgrowth.The results of experiments and variance analysis showed that the difference of cellulose content in seedcoat reached highly significant level, but the content of lignin and hull percentage nearly had no difference among the three pairs of materials.The difference in cellulose content between yellow- and black-seeded lines was not obvious during the growth of seed,but the differences in lignin content and hull percentage was up to highly significant level.So it could be concluded that the lower lignin content might be the reason for the lower hull percentage in yellow-seeded lines.3.some enzymes related to pigments and lignin in seedcoat were studied.The results of experiments and variance analysis showed that the activities of PAL,PPO,POD increased gradually in the early stage and decreased in late stage during the period of seed development.The activities of PAL,PPO,POD in black-seeded lines were much higher than those in yellow ones.lt was suggested that the activities of PAL,PPO and POD might have great effect on the formation of distinctive seedcoat features.The activities of PPO and POD reached climax at 41 DAF.The activity of PAL reached climax at 34 DAF.lt was indicated that PAL activity might mainly influence the content of some precursor.4.Some enzyme activities were repressed and formation of protein was modulated during the seed growth.The results indicated that the formation of distinctive seedcoat features was related to the shikimic-phenylalanine pathway and influenced by PAL activity,PPO activity and oxidation.5.The isozyme patterns of esterase,polyphenol oxidase(PPO) and peroxidase(POD) in seedcoat were investigated. Same or similar esterase isozyme bands were observed between black- and yellow-seeded lines under same genetic conditions;There were more PPO isozyme bands in black-seeded lines than in yellow ones and there was 1 special band in black-seeded lines;Black-seeded lines had 1 more POD isozyme band (b or c band) than yellow ones under same genetic conditions. Owing to different genetic background,the isozyme patterns of esterase.PPO an...