Expression of cold-related genes and physiological characteristics of the diploid and tetraploid non-heading Chinese cabbage.

Expression of cold-related genes and related physiological characteristics between the diploid and tetraploid non-heading Chinese cabbage was compared when both were under low temperature stress, so as to compare the cold-resistance difference of the diploid and the tetraploid from the level of gene expression, physiological and biological, photosynthetic characteristics, and agronomic traits. This study will provide a theoretical basis for the production of cold resistant tetraploid varieties. Differential expression of three cold-related genes CBF3, COR15 and ZAT10 was analyzed by qRT-PCR technique, and the activities of protective enzymes and the content of osmolyte at 0, 2, 6, 12 and 24 h were compared between diploid and the corresponding tetraploid non-heading Chinese cabbage when they were treated at the temperature of (4±1) °C. Net photosynthetic rate, stomatal conductance and transpiration rate were measured by the portable photosynthetic apparatus LI-6400, and chilling index and agronomic traits were surveyed and compared when both sides were under field conditions. The results showed that qRT-PCR analysis demonstrated that variation trend of the expression of three cold-related genes CBF3, COR15 and ZAT10 resembled each other between the diploid and the tetrapolid. All the expression quantity of the three cold-related genes of the tetraploid P8 showed significant up-regulation over time than the diploid P9. Trends of the activities of protective enzymes superoxide dismutase (SOD), peroxidase(POD), catalase(CAT)and osmolyte contents showed a single peak curve, that was to rise first than to decrease, both peaked at 12 h. The activities of SOD, POD, CAT increased 17.22%, 19.98% and 17.08% respectively more than P9. Moreover, the tetraploid always showed a higher activity and content than the diploid. The ability to eliminate reactive oxygen of P8 was better than that of P9. High synthesis rate was maintained so as to keep the content of osmolyte to resist the low temperature stress. Dynamic trends of the net photosynthetic rate, stomatal conductance and transpiration rate of the tetraploid showed similarity with that of the diploid and no photosynthetic noon break was noticed. Moreover, the tetraploid showed a higher index and all indices showed significant differences. Chlorophyll a, chlorophyll b and chlorophyll a/b of the tetraploid P8 increased 18.58%, 12.16% and 5.80% respectively with respect to those of the diploid P9. Plant weight, leaf weight/petiole weight, field yield and other six agronomic characters of the tetraploid showed significantly larger index than those of the diploid. Chilling injury index of the diploid and tetraploid were 26.0% and 18.0% respectively, and it showed significant differences. Conclusions:The expression quantity of three cold-related genes of the tetraploid were all significantly higher than those of the diploid, which led to the improvement of activity of protective enzymes, contents of osmolyte and cold resistance of the chloroplast, so as to maintain the higher photosynthetic ability of the tetraploid when it was under low temperature. Weight of per plant, field yield and other agronomic traits of the tetraploid showed better than those of the diploid, and the tetraploid manifested higher adaptability and high yield potential. [ABSTRACT FROM AUTHOR]