| With rapid development of modern industry and agriculture, an increasing amount of Cadmium is released into the environment, especially into farmland soils. The Cd contaminated soil may cause adverse effects to human health through food chain. Oilseed rape is a major oil crop widely grown in China. Recent studies have shown that oilseed rape is also a potential plant resource for phytoremediation of Cd contaminated soil. Therefore, screening high Cd accumulation oilseed rapes from rich germplasm resources of B. napus and B. juncea in China and studying the response and mechanism of different Cd-tolerance oilseed rape varieties to Cd stress has important realistic significance for further application of oilseed rape to phytoremediation of Cd contaminated soil. In this study, B. napus var61093,61042,61049and B. juncea var J281, J052, J192with different Cd tolerance, which were screened from plenty of rape cultivars through hydroponic culture experiment, were used to investigate the effects of different Cd trearments on their growth characteristics, antioxidant system, Cd uptake and accumulation, Cd speciations and seed quality by employing pot cultures. The preliminary mechanism of Cd tolerance among various oilseed rape varieties was discussed. The main results are presented as follows:1The six oilseed rape varieties had different tolerance to Cd. B.juncea varieties were more tolerant to Cd stress than the B. napus varieties. Among the six oilseed rape varieties, J281was the most tolerant one to Cd stress. B.napus var61049showed stronger tolerance to Cd than the other two B.napus varieties and the B.juncea var J052. There was a very good coordination between growth indexes and antioxidant systems of oilseed rapes at the seedling stage. The CAT activity, GSH concentration, soluble protein concentration of leaves showed a highly significantly positive correlation with relative biomass(r=0.785**, r=0.779**, r=0.758**), AsA concentration was significantly positively correlated with relative biomass(r=0.577*), while there was a highly significantly negative correlation between MDA concentration and relative biomass. Antioxidant system could reflect growth status and Cd tolerance of different oilseed rape varieties well.2The Cd uptake, translocation and accumulation of the six oilseed rapes at the three growth stages were various. At the seedling stage, the shoots Cd concentration of B juncea varieties were lower than that of B. napus varieties; However, Cd concentration in shoots of B.juncea varieties at the boilting and maturing stages gradually exceeded that of B.napus varieties. At the maturing stage, the shoots Cd concentration of B. juncea varieties and B.napus varieties under10mg/kg condition were71.31～100.86mg/kg and54.39～81.42mg/kg, respectively. Among six oil seed rapes, the shoot Cd concentration of J281was the highest (100.86mg/kg), which reached the standard for Cd hyperaccumulators (100mg/kg). Bioaccumulation of Cd in shoots of the six oilseed rapes increased with the extention of growth periods. Shoots Cd bioaccumulation of B.juncea var J281, J192and B.napus var61049with stronger Cd tolerance were higher than that of B.napus var61093,61042and B.juncea var J052with poorer Cd tolerance.3Cd concentration in organs of the six oilseed rape varieties ranked from high to low as:stem and leaf, root, seedcase and seed. There was a great difference among seeds Cd concentration of the six oilseed rape varieties. The seeds Cd concentration were0.00～1.54mg/kg for1mg/kg Cd teatment and0.08～3.57mg/kg for10mg/kg Cd treatment, respectively. Among the six oilseed rape varieties, the Cd concentration in seeds of B.juncea var J281was both the lowest under the two levels of Cd treatments. J281was an ideal plant for phytoremediation of Cd contaminated soil. The removal rate of Cd from contaminated soil by the six oilseed rape varieties increased with the extention of growth periods and reached maximum at maturing stage (2.52%-8.94%for1mg/kg Cd treatment;0.59%-2.32%mg/kg for10mg/kg Cd treatment). In consideration of phytoremediation efficiency, it was the best to harvest oilseed rapes at the maturing stage.4There were great difference among the proportion of various Cd speciation in stems, leaves and seedcases of four oilseed rape varieties at different growth stages. Cd speciation of stems and leaves were mainly in forms extracted by1mol/L NaCl and2%HAC, being58.77%～80.31%and55.30%～80.34%of total Cd concentration, respectively. The proportion of various Cd chemical forms in seedcase of the four oilseed rape varieties showed significant difference. Chemical forms in B.napus var61042and61049were mainly extracted by1mol/L NaCl and deionized water (75.39%～81.13%); the greatest amount of Cd in J281was found in the extraction of2%HAC and1mol/L NaCl (55.99%), followed by d-H2O (18.62%); in J192the greatest amount of Cd was extracted by d-H2O and the subdominant amount of Cd was extracted by1mol/L NaCl and2%HAC. The amount of Cd extracted by d-H2O and80%ethanol in rapeseeds of B.napus var61042and B.juncea var J192which both had high rapeseed Cd accumulation were significantly higher than that in B.napus var61049and B.juncea var J281with low rapeseed Cd accumulation. At the maturing stage, the amount of Cd which existed as soluble organic acid or inorganic nitrate, chloride forms in leaves and seedcases of61042were2.34and1.60times as much as that of61049, respectively, which in leaves and seedcases of J192was1.94and3.20times as much as that of J281, respectively.5Cd concentration in oil of the six oilseed rape varieties was less than that in cake. Cd treatments changed the fatty acid composition of rapeseed oil. Compared with control,1mg/kg Cd treatment significantly increased oleic acid content in rapeseed oil of J281by28.52%, and greatly decreased the content of palm acid, linoleic acid and linolenic acid by6.25%,6.74%and29.45%, respectively. Low Cd concentration treatment (1mg/kg) improved the nutritional value and the storage period of J281seeds to a certain extent. |
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