Effects Of Brassinolide And Its Complex On Cold Tolerance Of Zelkova Sinica

Zelkova sinica is a rare native specie in Shanxi province,which plays an important role in landscaping,soil and water conservation and so on.However,the cold tolerance of Zelkova sinica is poor.In practical cultivation process,it is difficult to survive safely in the winter.In this study,annual cutting seedlings were used as experimental materials,and were treated with distilled water（CK）,0.01mg/L BR（B1）,0.1mg/L BR（B2）and 0.1mg/L BR+10mmol/L CaCl₂（B3）through spraying on the leaf.The study analysis the cold response and get a comprehensive evaluation of the influence of brassinolide and its complex on the cold resistance of Zelkova sinica.Significantly,this study provides a scientific guidance and technical reference to improve the cold resisitance of Zelkova sinica and ensure their safety overwintering.The results are as follows:（1）The brassinolide and its complex increased the thickness of upper epidermis and palisade tissue,cell tense rantio,palisade tissue and spongy tissue ratio of Zelkova sinica.The leaf thickness,thickness of palisade tissue,cell tense rantio,the ratio of palisade and spongy tissue in B3 treatment were 1.28 times,2.22 times,1.18 times and 1.96 times higher than those in the control,respectively.（2）Brassinolide and its complex reduced the stomatal density and stomatal aperture of Zelkova sinica.With the change of temperature,stomatal density and stomatal aperture of Zelkova sinica decreased gradually.The stomatal density of each treatment was lower than the control,and the stomatal density of B2 and B3 was significantly different from the control.The stomatal density of B3 was the lowest,25.53%lower than that of the control.There was no significant difference in stomatal aperture at different time in the same treatment.（3）Brassinolide and its complex slowed down the decline of photosynthetic pigment in Zelkova sinica leaves.With the decrease of temperature,the content of photosynthetic pigment in different treatments decreased.The content of photosynthetic pigment in B2 and B3 was significantly higher than the control,and there was no significant difference between them.In November,the contents of chlorophyll a,chlorophyll b,total chlorophyll and carotenoid in B3 were 0.63mg·g-1,0.22mg·g-1,0.85mg·g-1,0.12mg·g-1,respectively.（4）Brassinolide and its complex had significant effect on cell membrane of Zelkova sinica.Different treatments significantly slowed down the rising trend of relative conductivity and MDA content of Zelkova sinica.After low temperature stress,the relative conductivity of branches in B3 treatment was 28.12%lower than the control,and the difference was significant.The MDA content was 27.97% lower than the control.The LT50 of leaves and branches in B3 treatment was the lowest among different treatments.The LT50 of leaves and branches in B3 were-36.51℃ and-24.76℃,respectively.（5）Brassinolide and its complex had significant effect on osmotic regulatory substances of Zelkova sinica.Compared with the control,the content of soluble protein,soluble sugar and free proline were increased by different treatments.With the passage of time,soluble protein in leaves and branches of B3 treatment increased at first and then decreased,while soluble protein in other treatments increased gradually.The soluble sugar content in leaves and branches of all treatments increased continuously.The free proline in leaves and branches of B2 and B3 treatment increased gradually,and there was no significant difference between them.（6）Brassinolide and its complex increased the activity of protective enzymes of Zelkova sinica.With the passage of time,the SOD activity of different treatments increased at first and then decreased.After low temperature stress,the POD activity in leaves and branches of all treatments decreased,and the POD activity in branches of B3 treatment decreased by 72.68% less than that of the control.Compared with the control,the CAT activity in leaves and branches of all treatments increased,and the difference between B2 and B3 was significant.The CAT activity in leaves and branches of B3 treatment increased more,increased by 0.33U·min-1·g-1,1.20U·min-1·g-1,respectively.（7）Brassinolide and its complex increased the cold tolerance of Zelkova sinica.The order of the cold resistance of Zelkova sinica was B3（0.1mg/L BR+10mmol/L CaCl₂）> B1（0.01mg/L BR）> B2（0.1mg/L BR）> CK.The cold resistance index and the average degree of membership of B3 treatment was the largest,and the effect of 0.1mg/L BR+10mmol/L CaCl₂ combination on the cold resistance of Zelkova sinica was the best.