| Radish （Raphanus sativus L.） is a semi-hardy vegetable, which is very popular withpeople. Radish seedlings often suffer high temperature stress in summer, resulting in yieldreduced significantly and even local failed. Previous studies indicated that exogenous salicylicacid （SA） and jasmonic acid （JA） could improve the stress resistance and ease adversity stressof plants in some degree. Therefore, it has important theoretical and practical significance forsummer cultivation of radish to select varieties suitable for summer cultivation and elucidatethe mechanism of SA and JA improving the heat tolerance of radish.This experiment had collected some radish varieties （which were provided by VegetableResearch Institute of Shandong Academy of Agricultureal Sciences） and identified their heattolerance. On this basis, we selected different heat tolerance radish varieties and researchedthe physiological response of them to high temperature stress, in order to explore the differentheat tolerance mechanisms. Meanwhile, to lay the theoretical foundation of alleviating heatinjuries, the effects of high temperature stress to physiologic and biochemical indexes ofradish seedlings under treatment of exogenous SA and JA were studied. The main results areas follows:1. The heat tolerance differences between radish varieties were well reflected byelectrolytic leakage and heat injury index and had negative correlation with them under hightemperature stress. In the testing varieties, electrolytic leakage and heat injury index of‘Wuzibiekedongluobo’ were the highest, while ‘Xiamidao’ were the lowest. The results ofelectrolytic leakage and heat injury index were consistent. The results showed that‘Wuzibiekedongluobo’ was the high temperature sensitive variety and ‘Xiamidao’ was thehighest tolerance to high temperature.2. The electrolytic leakage, the contents of MDA, IAA, GA and the activities of POD andAPX of ‘Xiamidao’ were lower than these of ‘Wuzibiekedongluobo’, in contrast, the contentsof soluble sugar, proline, SA and the activities of SOD and CAT and the reduction range ofosmotic potential were higher than ‘Wuzibiekedongluobo’. The electrolytic leakage and theMDA content in ‘Xiamidao’ leaves recovered to pre-treatment levels under the normaltemperature treatment for4days, while the two indexes in ‘Wuzibiekedongluobo’ were increased compared to before treatment. These results suggested that heat-tolerance varietyavoided the injury caused by high temperature stress by reducing electrolytic leakage, osmoticpotential and MDA content, accumulating osmotic adjustment materials and increasing theactivity of SOD and the content of SA.3. The pretreatment with different concentration SA from50to150μmol·L-1couldsignificantly reduce the electrolytic leakage and raise the contents of soluble sugar and prolineof radish seedlings under high temperature stress. And the effects of75μmol·L-1SA was mostsignificant. After pretreatment with75μmol·L-1the contents of soluble sugar and proline wereup-regulated as the time extended and the activities of SOD, CAT and APX and the contentsof ABA and SA were also significantly increased compared with the control. However, theelectrolytic leakage and the contents of MDA, IAA and GA were significantly lower than thecontrol. The activities of SOD, CAT and APX were higher than the control under normaltemperature. These results indicated that application of exogenous appropriate concentrationSA not only enhanced the ability of heat tolerance by reducing the leakage of electrolytic andperoxidation product of MDA, increasing the contents of osmotic adjustment materials andhormones but also promoted radish seedlings growth by increasing the activities ofantioxidant enzyme.4. The electrolytic leakage was also decreased and the contents of soluble sugar andproline were also increased by the application of50to150μmol·L-1SA in leaves of radishseedlings under high temperature stress, and the effects of75μmol·L-1SA was mostsignificant. In addition, the activities of antioxidant enzyme and the contents of SA and ABAin leaves of radish seedlings under75μmol·L-1JA treatment were significantly higher than thecontrol, while the contents of MDA, IAA and GA significantly lower than the control. Thecontents of hormones were higher than the control after recovered normal temperaturetreatment, indicating that when plant suffered from stress, the plant could recovered growthrapidly through accumulating hormones by application exogenous JA. In sum, JA couldimproved the heat tolerance ability of radish seedlings by alleviating rising speed ofelectrolytic leakage and MDA content, promoting the accumulation of soluble sugar andproline, decreasing osmotic potential and increasing the activities of antioxidant enzyme andthe contents of relative hormones. |
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