Effects Of Artificial Cold Acclimation On The Cold Tolerance Of Azaleas

Azalea(Rhododendron spp.)is a traditional Chinese famous flower,widely used in landscape or potted ornamental.Its cold tolerance and mechanism research for the application of azalea scope and breeding work is of great significance.The azalea cultivars 'Elsie Lee'(Rhododendron 'Elsie Lee')and 'Yudaizhirong'(Rhododendron'Yudaizhirong')are hybrids under the Subgen Tsutsusi.It has been proved that these two varieties have good performance and strong cold tolerance in the course of natural overwintering,and the effect of artificial low temperature cold acclimation on their cold tolerance is further discussed in this study.The main results are as follows:1.A comparative study on the cold tolerance of two azalea cultivars during artificial cold acclimation at 4?Through artificial 4? low temperature cold acclimation treatment for 56 d,found that 'Elsie Lee' has better cold tolerance,and after cold acclimation,the change of cold tolerance and physiological changes more significant.It can be used as a typical variety to further study on the related mechanism of the cold tolerance of rhododendron.By comparison,we know that the LT50 of 'Elsie Lee' is always lower than the'Yudaizhirong',the change in the process of cold acclimation is greater,the change is faster,the LT50 in the latter 'Yudaizhirong' is basically stable and the LT50 of'Elsie Lee',is still changing,which shows that'Elsie Lee',has greater cold tolerance potential.2.A comparative study on the cold tolerance of 'Elsie Lee' during cold acclimation at constant and variable temperaturesTaking 'Elsie Lee'as the test material,in the artificial variable temperature condition that is 10/4?(day/night)to carry on the cold acclimation 56 d.The result shows that in the early period,that is 7-14 d,cold tolerance performance of two conditions are same.In other phases,the change of cold tolerance under variable temperature was greater than that of constant temperature.In the whole cold acclimation process,the variation of LT50 under the variable temperature condition was greater than the constant temperature condition.From the perspective of physiological changes,the physiological activities of plants were more active under the condition of variable temperature.By comparing the dynamic changes of total soluble sugar and starch.it was found that the increase of total soluble sugar content in cold acclimation under constant temperature mainly came from the hydrolysis of starch,while the increase of total soluble sugar content in cold acclimation under variable temperature also partly came from metabolic synthesis.Low temperature weakened the photosynthesis of rhododendron,and after a period of cold acclimation,the photosynthesis of rhododendron recovered more under the condition of variable temperature.It was found from the change of chlorophyll content that the value of Ca/Cb had a parallel relationship with the change of cold tolerance,which could be used to judge the change of the cold tolerance of rhododendron.LT50 and various physiological indexes of correlation analysis results show that the constant and variable temperature acclimation in the differences between each index and the correlation of cold tolerance.Under the condition of constant temperature,water content,total soluble sugar content,starch content and Ca/Cb value changes of'Elsie Lee' are closely related to the cold tolerance.Under the condition of variable temperature,water content,total soluble sugar content and chlorophyll content changes of'Elsie Lee' are closely related cold tolerance.3.A study on the changes of dehydrins during the cold acclimation in 'Elsie lee'In the process of cold acclimation,dehydrin has been repeatedly proved that there is a close relationship with cold tolerance.For rhododendron leaf protein extraction in the organization.and tried out four methods in this experiment,modified phenol extraction method is a kind of method that is convenient,efficient,high quality.It is the most suitable method for rhododendron leaf protein extraction.Used for SDS-PAGE and Western Blot detection has good results.Modified phenol method was used to extract proteins from the leaves collected in the constant temperature and variable temperature cold acclimation test.And Western Blot detection of dehydrin showed that 9 dehydrins were successively expressed under the two low temperature conditions,with the protein size ranging from 17 to 120 kDa.And the proteins of the same size appeared in different periods under different conditions.In the cold acclimation process,the expressions of two dehydrins,40 kDa and 38 kDa,increased with the increase of cold tolerance under constant temperature,and the expressions of dehydrins,102 kDa and 89 kDa,increased with the increase of cold tolerance under variable temperature,representing that the changes of cold tolerance can be estimated according to the corresponding dehydrins under the two conditions.All the proteins of 17 kDa appeared in the final stage of cold acclimation,during which the cold tolerance was significantly improved,representing that this dehydrin could only be induced after a long period of cold acclimation,and it may play an important role in the improvement of cold tolerance.