| Four scallion cultivars, Jiyewanchou, Chunwei, Changyue, which are summer scallion cultivars with higher heat tolerance, and Zhangqiu with lower heat tolerance were chosen as experimental materials. In order to provide theoretical foundation for scallion breeding with high heat tolerance, physiological parameters, such as membrane permeability, contents of soluble materials, chlorophyll a fluorescene transient and antioxidant enzyme activities were measured under different temperature treatments. The main results are as follows:1. Effects of high temperature stress on the biomembrane systemThe half-damage temperature of Jiyewanchou, Chunwei, Changyue and Zhangqiu was 46.4℃, 47.5℃, 46.1℃and 44.2℃, respectively, which showed that Chunwei had the highest heat tolerance, while Zhangqiu was most susceptible, and heat resistance varied remarkably among the four cultivars.High temperature stress destroyed the membrane integrity and stability, and ultimately resulted in evident increase in MDA content, a product of membrane-lipid peroxidation. With the increase of temperature, the increased MDA content in the four summer scallion cultivars was observed. When the stress temperature reached to 50℃, compared with the state of 25℃, the MDA content of Jiyewanchou, Chunwei, Changyue and Zhangqiu had increased by 98.1%, 75% 95.1% and 103%, respectively. This result revealed that the biomembrane of three summer scallion cultivars were injured more slightly than that of Zhangqiu.2. Effects of high temperature stress on contents of soluble materialsThe contents of proline and soluble sugar increased along the increase of stress temperature, which enhanced osmotic adjustment. When the temperature reached to 40℃, the obvious increase of proline was noted. When the temperature reached to 50℃, compared with the state of 25℃, proline content of Jiyewanchou, Chunwei, Changyue and Zhangqiu increased by 7.03, 10.2, 7.86 and 5.29 times, respectively, which showed that the increase of proline content in three summer scallion cultivars was far more than that of Zhangqiu. Meanwhile, the changing trend of soluble sugar was similar to that of proline.3. Effects of high temperature stress on antioxidant enzyme activitiesWith the increase of the stress temperature, activities of the four antioxidant enzymes, SOD, CAT, POD and APX in the scallion leaves, increased at first and then decreased. The decrease extent declined in the order of Zhangqiu, Changyue, Jiyewanchou and Chunwei. Under moderate high temperature, because of stress reaction, antioxidant enzyme activities increased to eliminate a large amount of active oxygen. With further increase of stress temperature, the stress degree was enhanced and the enzyme activities decreased. It was speculated that the stress had surpassed the enduring degree of the scallion leaves, leading to the decrease of antioxidant enzyme activities. The decrease of antioxidant enzyme activities made the further production of active oxygen, which would seriously destroy biomacromolecule and biomembrane.4. Effects of high temperature stress on content of chloroplast pigment and PSⅡfunctionDuring high temperature stress, the contents of Chla, Chlb and Car in the scallion leaves declined obviously. Contents of Chla, Chlb and Car in Zhangqiu decreased most severely, whereas those in Chunwei decreased most slightly, meanwhile Jiyewanchou and Changyue with little difference.With the increase of stress temperature, the Fv/Fm and PIABS in leaves of the four cultivars all declined, in the order of Zhangqiu, Changyue, Jiyewanchou and Chunwei .The DIo/CSo of the four cultivars increased with the increase of temperature. The increase of DIo/CSo in Zhangqiu was larger than the other three. ETo/CSo and TRo/CSo decreased with the increase of temperature. The decrease of TRo/CSo and ETo/CSo in Zhangqiu were the largest, whereas the decline of TRo/CSo in Chunwei were the smallest, meanwhile Jiyewanchou and Changyue with little difference. After high temperature stress, the ETo/CSo of summer scallion cultivars were higher than that of Zhangqiu, which indicated that the photosynthetic activity per elemental area of summer scallion cultivars were subjected to minor injury.Injured degree of oxygen evolution complex could be evaluated by Wk. The larger Wk was, the more injury oxygen evolution complex had been subjected to. With the increase of stress temperature, increase of Wk in the four cultivars were in the order of Zhangqiu , Changyue, Jiyewanchou and Chunwei , which revealed that the injured degree of oxygen evolution complex in Chunwei was the slightest.5. The alleviation function of salicylic acid on high temperature stressTaking Chunwei as experimental material, the pretreatment by 10mmol/L salicylic acid could obviously alleviate the harm on the scallion leaves caused by high temperature. Under high temperature stress, exogenous salicylic acid treatment could raise the half-damage temperature of the leaves of scallion seedlings, enhance the antioxidant enzymes activities, make the PSⅡcenter more stable and alleviate photoinhibition.
|
PDF Full Text Request