| Maize is the main food crop in the northeastern of China,but the germination of maize seeds and the growth of seedlings are often hurt by low temperatures because the weather is usually unstable in early spring.In this study,maize varieties with different cold resistance were screened by indoor seed germination experiment under low temperature and field sowing experiment in early spring.The effects of exogenous soaking agent on seed germination,seedling growth and physiological and biochemical characteristics of maize were studied.On this basis,the effects of exogenous abscisic acid(ABA)on the expression of proline synthesis related gene P5CS was studied in detail,and the molecular mechanism of improving the cold resistance of maize was discussed initially.The main results are as follows:1.Nine leading varieties in Liaoning province,including Zhengdan 958,were used as experimental materials.The germination rate,germination potential,germination index,vigor index and seedling height and fresh weight of the cultivars were decreased under low temperature by the indoor germination experiments,and the lower the temperature,the greater the inhibitory effect on each germination index.The low temperature in early spring could decrease the seedling emergence rate,reduce the plant and the ear heights,shorten the spike,cut down the diameter of ears,decrease the number of rows and the hundred-grain weight,so the total yield decreased in the field.Based on the above indexes,Zhengdan958 is the most cold resistance variety and Danyu 39 is the most sensitive variety to low temperature.2.The effects of salicylic acid(SA),polyethylene glycol(PEG),inositol,CaCl2,H2O2,ABA and gibberellin on seed germination and physiological and biochemical indexes of maize under low temperature stress were studied using Zhengdan 958 and Danyu 39 as experimental materials.The results showed that ABA had the best effect on raising seed germination rate and seedling proline content,CaCl2 had the most prominent effect on promoting seedlings stronger,and SA had the most prominent effect on improving the protective enzyme activity,soluble protein and chlorophyll content of seedlings under low temperature stress.3.Based on ABA,SA,CaCl2,ten compounds of seed soaking agents were prepared combined with orthogonal test design.The effects of compounds on seed germination and seedling physiological and biochemical indexes of Zhengdan 958 and Danyu 39 under low temperature stress were studied.The results showed that the combined effect of compound 8 on the indexes of maize under low temperature stress was the best.Compared with the control,to Zhengdan 958,the germination rate,germination potential,germination index and vigor index were increased by 22.5%,31.8%,37.9%and 149.2%respectively,the plant height and seedling fresh weight increased by 69.4%and 80.8%respectively,the activities of POD,SOD and CAT increased by 31.2%,18.5%and 30.7%respectively,the content of proline,protein and chlorophyll increased by 18.4%,15.2%and 35.3%respectively,and the content of malondialdehyde decreased by 16.2%.While for Danyu 39,the germination rate,germination potential,germination index and vigor index were increased by 40.4%,53.8%,64.3%and 170.9%respectively,and the plant height and seedling fresh weight increased by 43.0%and 64.6%respectively,POD,SOD and CAT activities were increased by 27.4%,25.3%and 36.1%respectively,the content of proline,protein and chlorophyll increased by 35.8%,9.8%and 25.3%respectively,and the content of malondialdehyde decreased by 19.0%.The compound 8 could significantly improve the cold resistance of two varieties of maize.4.The effect of ABA on the proline metabolism of maize seedlings was studied by using ABA solution to treat maize seedlings under low temperature stress.The results showed that the activities of P5CS and OAT increased and the activity of ProDH decreased under low temperature stress.ABA treatment was beneficial to the accumulation of proline and the increase of P5CS activity,and decreased ProDH activity.OAT activity was not affected much by ABA.On this basis,the expression of P5CS gene was analyzed by semi-quantitative RT-PCR.ABA treatment could significantly increase the expression of P5CS,which promoted the synthesis of proline and improved the cold resistance of maize seedling. |
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