Comparison of vitality between seedlings germinated from black-coated and yellow-coated seeds of a turnip rape (Brassica rapa L.) subjected to NaCl and CdCl2 stresses

Yellow-seeded (YS) rapeseed varieties have attracted considerable interests from cultivators because of their thin seed coat and high seed oil content. However, compared with black-seeded (BS) rapeseed, little is known about the response of YS rapeseed to abiotic stresses. In this study, we characterized the cellular structures of YS varieties and BS varieties and the physiological parameters of the YS and BS seedlings subjected to high-salt and/or high-cadmium conditions. We observed larger and denser (in arrangement) oilbodies in YS than in BS varieties. The BS variety seed coat was much thicker than that of the YS variety because of the existence of a palisade layer where pigments are deposited. Either at the eighth day or 1 month after sowing, YS seedlings showed higher sensitivity to NaCl and/or CdCl2 stress than BS seedlings, as reflected by the length of roots, biomass, and a variety of physiological parameters, including MDA, chlorophyll content, and antioxidant activities. Our results suggested that the more vigorous growth of BS seedlings is likely due to the higher flavonoid content in their vegetative tissues, and the poor performance of YS seedlings under stress treatment (especially with NaCl) could be attributed to its relatively low flavonoid content. Our findings raise some points that need further investigation to obtain an in-depth understanding of the molecular mechanisms involved.