Abstract:

The seed coat color has been thought to be closely concerned in the polyphenols. The content differences of polyphenols between yellow and black seed coats have been determined in Brassica napus, but not in Brassica juncea. In addition， the molecular structure differences of polyphenols between yellow and black seed coats seem not to be reported in Brassica. Plant polyphenols are a large number of complex compounds containing hydroxyls, they play an important role in physiological actions in plant organism. To find out the content differences and the molecular structure differences of polyphenols between yellow and black seed coats, and the relationship between the polyphenols’ differences and the seed coat color differences in B. juncea the yellow and black seed coats of inbred lines of B. juncea were used as the research materials， the solutions of the polyphenols extracted from the yellow and black seed coat samples with 5% HCl-CH3OH were scanned by the UV-Vis spectrophotometer(UV-1600) at wavelength of 200–300/800 nm, and the contents of polyphenols were determined through absorption spectrometry with either gallic acid or tea catechin standard， respectively. The results showed that the content of polyphenols of the yellow seed coat was about 90% of that of the black seed coat. While the content of polyphenols of the yellow seed coat was about 10% of that of the black seed coat in B. napus. Therefore the high content of polyphenols might be the main factor resulting in the character heredity stability of yellow rapeseed in B. juncea. In vanillin test the black seed coat turned red in color， the yellow coat remained the original color. It could be deduced that there are the flavanol-phenolic molecules that their ring C should contain 3-OH among the polyphenols of the black seed-coat, while there are not these molecules among the polyphenols of the yellow seed-coat. After the shift reagents were added in the solutions of the polyphenols extracted from the yellow and the black seed-coats， the spectral absorption band Ⅰ&Ⅱ shifted. On basis of the shift direction and the shift quantity of the spectral band Ⅰ&Ⅱ it could be deduced that phenolic ring A of the flavanol-phenolic molecules might contain monohydroxyl (7-OH) and o-dihydroxyl among the polyphenols of the yellow and the black seed-coats, respectively. It is proposed that the structural differences of the polyphenols might be the major factor resulting in the color differences between the yellow and the black seed coats in B. juncea. These results above may be significant not only in the yellow rapeseed breeding in B. juncea but also in trying to solve the unstable character heredity of the yellow rapeseed in B. napus.

Key words: Brassica juncea, Seed coat color, Polyphenols, UV-Vis spectrum, Shift reagent