| Radish(Raphanus sativus L.), an annual biennial herb which belongs to the genus Raphanus of the family Brassicaceae, is one of the main vegetable crops in china. High temperature is the main limiting factor for radish production in summer. One of the effective ways to guarantee summer production of radish is to study the heat resistance of radish and select cultivars of strong heat resistance. In the study, the heat resistances of radish were analyzed from these four aspects.The comprehensive identification of radish cultivars was conducted by field identification and simulated identification. In the field identification, the single root weight and the expanding rate of radish taproot was recorded and analysed to indentificate the heat tolerance of different cultivars. It was indicated that 17 cultivars were of strong heat resistance,9 cultivars were heat sensitive and 7 cultivars were of moderate heat resistance. In the simulated identification, Heat Injury Index (HI) and the Survival Rate of radish seedlings after high temperature stress were analyzed. It was indicated that His were lower in heat resistant cultivars than those in heat sensitive cultivars after 36℃stress for 6 days. After 2h exposure to 53℃, the survival rates of heat resistant cultivars were much higher than those of heat sensitive cultivars. The heat resistance of different radish cultivars can be distinguished effectively by comprehensive analysis of HI and survival rate after high temperature treatment.Under high temperature stress(38℃), the variation of MDA, soluble protein, soluble sugar and free praline contents in radish seedling of different heat resistances was analyzed.. Before the stress, the soluble content was higher in heat resistant inbred lines than that in heat-sensitive ones, while the content of soluble sugar, free praline and MDA exhibited no significant difference among inbred lines. Under the treatments of 38℃for 24h,48h and 72h, the contents of soluble protein, soluble sugar and free proline in heat resistant lines were significantly higher than those in heat-sensitive ones, while the MDA content was lower in heat resistant materials. Under the treatment of 38℃for 24 hours, the contents of all the four indexes were significantly increased. The soluble protein content declined continuously for 48h and 72h, but it declined much slowly in heat resistant lines. As compared with the treatment of 38 "C for 24h,, the contents of soluble sugar, proline and MDA were significantly higher for 48h in heat-sensitive materials, while in heat resistant materials, there were no significant increases for 48h and 72h. It was suggested that the variation of these four indexes was related with the heat resistances and could be used for evaluation of heat resistance in radish seedlings.The radish HSP17.7 gene was cloned by EST assembling, PCR and DNA sequencing. It was indicated through NCBI alignment that radish HSP17.7 sequence was highly homologous to turnip HSP17.6. The HSP17.7 gene had an open reading frame of 468bp, which encodes 155 amino acid, having a molecular weight of 17.7kD as predicted in ExPASy data base. Expression profiling of the HSP17.7 indicated that there were no detectable expression in radish leaves under nomal condition, while it was highly expressed when exposed for 1h to 40℃. It suggested that induction was indispensable for the expression of HSP17.7. Three HSP70 sequence fragment was acquired by specific primer amplification. HSP70-1A and HSP70-1B was amplified through the same primer, it was likely that they belonged to different members of the HSP70 gene family. The NCBI alignment indicated that all the 3 fragments had high homologies with HSP70 genes in Cruciferae Crops such as Arabidopsis thaliana.RAPD, ISSR and SRAP molecular markers were used for cultivar identification and genetic diversity analysis of heat resistant radish cultivars in china. Totally 333 bands were amplified and 210 (63.06%) were polymorphic. The SRAP primer of em1-1/me4, along with em16-1/me3 could distinguish all 31 radish cultivars. Analysis of genetic similarity coefficient showed that radish cultivars had a near genetic relationship with a narrow genetic background. Cluster analysis showed that genetic relationship among cultivars was highly related to skin color, tap-root morphology, heat resistance and geographic distribution. It is indicated that molecular markers can be used for radish cultivar identification and genetic diversity analysis. A reliable identification could be acquired with multiple molecular marker analysis. |
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