| In this paper, the genetically stable tetraploid was obtained from induction and identification of the diploid non-heading Chinese cabbage ’Nanjing Si Yue Bai’. Meanwhile, qRT-PCR technique was used for analysis of differential expression of three cold-related genes CBF3, COR15 and ZATIO in diploid and tetraploid non-heading Chinese cabbage P9 and P8 when both were under low temperature stress. Cold resistance and physiological characteristics of the tetraploid were analyzed from the level of gene expression, physiological, biochemical and photosynthetic characteristics and agronomic traits, which will provide a theoretical foundation for production and applications of cold-resistant tetraploid varieties.Different concentrations of colchicine were dripped on the growing point of the diploid non-heading Chinese cabbage ’Nanjing Si Yue Bai’(Brassica campestris ssp. chinensis Makino,2n=2x=20) which was in the cotyledon period. The genetically stable tetraploid was obtained by ploidy identification, which was based on morphology, anatomy and cytology means. The results showed that:The best induced mutagenesis of the tetraploid was 8.1% when the colchicine concentration was 2 g·L-1.and the processing time was six. Compared with the diploid, the tetraploid performed significantly "Giant" in flowers, pores, pollen and other aspects. DNA relative content of the tetraploid was 600 and the chromosome number was 2n=4x=40, which was about twice of that of the diploid.Differential expression of three cold-related genes CBF3, COR15 and ZAT10, the activity of protective enzymes, that is superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) and content of osmolyte that is soluble sugar, soluble protein, free proline, as well as MDA content and electrical conductivity at 0,2,6,12,24 h were compared between diploid and corresponding tetraploid non-heading Chinese cabbage when both were treated at the temperature of (4±1)℃. The results showed that:(1) qRT-PCR analysis demonstrated that the expression level of cold-related genes CBF3, COR15 and ZATIO in leaves of tetraploid were significantly higher than that in the diploid. (2) Trends of the activity of protective enzymes SOD, POD, CAT and osmotic contents showed a single peak curve, that is to rise first than to decrease, both peaked at 12 h. The activity of SOD, POD, CAT of P8 was 3.20,279.25 and 268.70 U·g-1·min-1 respectively, which increased 17.22%, 19.98%,17.08% compared to P9, respectively. Soluble sugar, free proline and soluble protein content of P8 was 40.12,0.24 and 42.67 mg·g-1 respectively, which increased 17.28%,15.31% and 15.89% with respect to P9, apartly;Content of malondialdehyde and electrical conductivity of P8 was 0.39 mg·g-1 and 12.8%, which reduced 13.23% and 32.03% compared to that of P9. Content of soluble sugar, soluble protein and proline of the tetraploid were always higher than that of the diploid, while MDA content and electrical conductivity were always lower than that of the diploid.Content of chloroplast pigment, photosynthetic characteristics, chilling index and agronomic characters were compared when both the diploid and tetraploid were under field conditions. The results demonstrated that:(1) Chlorophyll a, chlorophyll b and Chlorophyll a/b of the tetraploid P8 were higher than that of the diploid P9. Dynamic trends of the net photosynthetic rate, transpiration rate, stomatal conductance of the tetraploid were consistent with that of the diploid. Moreover, the tetraploid showed a higher index; Intercellular CO2 concentration of the tetraploid P8 was always lower than the diploid P9, both showed significant difference. All the indicators showed significant differences. (2) Chilling injury index of the diploid P9 was 26.0%, which was 18.0% of tetraploid P8 and the difference was significant; Bolting time of the tetraploid P8 was later than P9. (3) Plant weight, leaf weight/petiole weight, field yield and other six agronomic characters of the tetraploid were significantly higher than that of the diploid. (4) Contents of Vitamin C, nitrate, dry matter, soluble sugar and protein in tetraploid P8 increased 18.62%,25.23%, 26.12%,19.87% and 30.05% respectively compared to the diploid P9. Contents of nutrition indicators showed significant differences. The tetraploid showed integrated cold resistant and high yield performance than the diploid. |
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