Physiological Mechanism Of Low Temperature Tolerance In Melon Seeds During Germination

Cucumis melo L.is a kind of cold sensitive crop,which is very cold resistant,and its primary origin centers are in tropical regions such as Africa and India.Low temperature stress often occurs in winter and spring production,which restricts the normal growth and yield formation of muskmelon.The germinating ability of melon seeds is different at different temperatures.Therefore,it is of great significance for evaluating the low temperature tolerance of melon seeds and early screening and evaluation of germplasm resources if the seeds can be treated at different temperatures from the germination stage to select the materials that can germinate at lower temperatures.In the process of seed germination,macromolecular substances such as lipids,starch and storage proteins are gradually hydrolyzed into soluble small molecules,which can be utilized in the seed germination process to complete the germination process.Therefore,studying the response and resistance mechanism of different melon seeds during germination process to cold stress can provide a theoretical basis for cold resistance breeding and early screening of melon germplasm resources.In this study,two muskmelon cultivars’ Thy ’and’ IVF521’,which had different responses to low temperature during seed germination,were used to study the germination of the seeds of the two cultivars at room temperature and low temperature and the physiological and biochemical changes during the germination process.The main results are as follows:1.Take 15℃ as the low temperature treatment and normal temperature as the control temperature.At room temperature of 28℃,the germination rate of ’Thy’ seeds was faster than that of ’IVF521’ seeds,but there was no significant difference in germination rate.The germination rate of ’Thy’ began to germinate at 84 h,and the germination rate was 11.7%.At 108h,the germination rate of ’Thy’ increased to 51.7%,while the germination rate of’IVF521’ was always 0.The germination rate of both varieties was significantly increased after 24 h of normal temperature restoration.91.7%and 96.7%,respectively.2.Under normal temperature,the soluble protein of ’IVF521’ and ’Thy’ varieties had no significant change during 0h to 24h,but increased sharply during 24h to 36h.Under low temperature,the soluble protein of the two varieties showed a downward trend overall,but increased significantly after returning to normal temperature treatment.Soluble protein had no obvious effect on seed germination in the early stage of seed germination,but had more significant effect on seed germination in the exposed stage of seed.There were 17 kinds of amino acids in melon seeds at different temperatures,among which aspartic acid,glutamic acid and proline were the most abundant.Under different temperature conditions,arginine,alanine,glycine,histidine,serine and threonine in the two varieties all showed a significant increasing trend at the late germination stage,and more than 50%amino acid levels in ’Thy’variety were higher than those in ’IVF521’ variety.3.Under different temperature conditions,starch content of both melon varieties showed a decreasing trend during seed germination;At low temperature,the soluble starch showed a decreasing trend at the initial stage of germination.The soluble starch content of’IVF521’ increased first and decreased from the middle stage to the late stage of germination.However,the soluble starch content of’THY’ had no significant change in each germination stage.At room temperature,the sucrose content of seeds of both varieties showed a decreasing trend during germination.There was no significant difference between glucose and fructose.The sucrose content of’IVF521’ variety was significantly higher than that of ’Thy’ variety at low temperature.The neutral invertase(NI)activity of the two varieties at late germination stage was significantly increased after different temperature treatment,and the difference was significant between the two varieties.Moreover,the expression level of CmNIS in ’Thy’ variety was significantly higher than that in ’IVF521’variety during the whole germination stage,suggesting that Ni and its gene family may play an important role in the seed germination process.4.The levels of ABA and 10 kinds of GAS in seeds of two melon varieties were determined and analyzed.Except for GA1,GA3 and GA7,the other 7 kinds were involved in the seed germination process.Under low temperature,the proportion of total GAs in’IVF521’ variety showed a trend of first increasing and then decreasing during seed germination,but there was no significant difference from that at 0 h of germination.The proportion of total GAs in ’Thy’ variety showed a significant decreasing trend during seed germination,while the proportion of ABA showed an opposite trend.The levels of GA9,GA15 and GA53 in different varieties are significantly higher than those of other types of GAS.Under low temperature,the levels of ABA,GA9 and GA15 in ’Thy’ seeds were higher than those in ’IVF521’ seeds,while the levels of GA53 were opposite.During germination,ABA levels of the two varieties showed no significant change at low temperature stage,but significantly increased after normal temperature was restored,while GA9 and GA15 levels showed a significant trend of decrease.5.Trehalose immersion test showed that trehalose immersion had no significant effect on seedling emergence of the two varieties at room temperature;Under low temperature,it had significant inhibition on variety 521,but not on ’THY’.