Effects Of 5-azaC On The Flowering And Physiological Indexes Of Rhododendron Hybridum

In this study,Rhododendron in different growth stages were treated with 5-azaC in various concentrations(0mg/L,50mg/L,100mg/L,150 mg/L,200mg/L).To detect the influences of 5-azaC on the flowering of Rhododendron,the bud differentiation,time of flowering,and changes in the physiological indexes were measured by paraffin sections.Several conclusions can be drawn from this study:1.When Rhododendron were sprayed with 5-azaC in their flower bud dormancy,the flowering stage was delayed by 4 to 11 days,and 9 to 13 days more than the control group.The 1 00mg/L treatment group had the longest flowering stage,which was 13 days more than the control group.The time of flowering was delayed by 11 days in the 200mg/L treatment group,nevertheless,the flowering stage was 3 days less than the control group.Thus,the 1 00mg/L treatment had the best effect on flowering time delay and flowering stage extension.2.In the flower bud dormancy stage,when treated with different concentrations of 5-azaC,the DNA methylation level of buds was significantly decreased,by 20.4%,26.1%,33.8%,43.9%,51.5%with respect to 0mg/L,50mg/L,1 00mg/L,150mg/L,200mg/L treatment.After the dormancy stage,the DNA methylation level of buds raised to some extent.The DNA methylation level of the control group was higher than the treatment groups.According to the statistical analysis,the DNA methylation level of flower bud significantly dropped in different 5-azaC treatment groups,among which the 200mg/L treatment group decreased most.3.When Rhododendron was treated with different concentrations of 5-azaC in the period of bud dormancy,the soluble sugar content in leaves increased first and then decreased from the dormancy stage to the flowering stage.After the 5-azaC treatments,soluble sugar content in the leaves descended significantly(p<0.05).4.Similarly,the soluble protein content in leaves also increased first and then decreased after treated with different concentration of 5-azaC.The soluble protein content in leaves was significantly higher(p<0.05)than that in the control group after the treatments.5.When treated with different concentrations of 5-azaC in the period of bud dormancy,the POD activity of Rhododendron leaves increased significantly,while the MDA decreased significantly.6.In the flower bud dormancy period,with 1 00mg/L 5-azaC treatment,the correlation among physiological indexes of Rhododendron differed as the plant grew.Before treatment,the DNA methylation level were positively correlated with and soluble sugar content,negatively correlated with POD activity,while soluble sugar content and POD activity was negatively correlated.All these correlations were highly significant.After 20 days of treatment,the correlation between MDA content and soluble protein content was significantly negative.After 40 days of treatment,the correlation between soluble sugar content and POD activity was significantly positive,while the correlation between DNA methylation level and MDA content was significantly negative.After 60 days of treatment,the correlation between DNA methylation level and one of the three indicators(soluble protein content,POD activity,and MDA content)was significantly positive,while the correlation between DNA methylation level and MDA content was significantly negative.After 80 days of treatment,the correlations between DNA methylation level and soluble protein content,MDA content were significantly positive,while the correlation between soluble protein content and MDA content was significantly negative.7.The differentiation of Rhododendron flower bud started at early July and ended at the last ten-day period of August.The differentiation started earlier after 5-azaC treatments.The 200mg/L treatment had the largest effect on advancing the differentiation time,other treatments ordered as 100mg/L>150mg/L>50mg/L based on the amount of time ahead,which were 12 days,9days,and 6 days respectively.In the period of vegetative growth,the differentiation times of treatment groups were 14-17 days ahead,relative to the time of the control group.Little differences were observed among the treatment groups.The differentiation time of treatment groups were 6-9 days less than the control group.Generally,the 100mg/L treatment had the largest effect on the differentiation time of Rhododendron flower bud.8.In the period of vegetative growth,the time of flowering was 11-16 days ahead in the treatment groups,and the time of blooming was 6-20 days ahead.150mg/L treatment group had the longest flowering period,which was 15 days more than the control groups.While flowering period of 200mg/L treatment group was 2 days less than the control groups.These results suggested that the flowering period of Rhododendron could be extended with 5-azaC treatment in certain concentration(e.g.150mg/L),while shortened with excessive concentration of 5-azaC treatment(e.g.200mg/L).Thus,in the period of vegetative growth,150mg/L treatment had the best effect on the flowering period of Rhododendron.9.From the vegetative growth stage to the early stage of flower bud differentiation,the DNA methylation level was increased,however,it decreased in the treatments groups(20.8%,27.3%,37.7%,51.7%,respectively).The DNA methylation level decreased most in the 200mg/L treatments group(37.7%).From the vegetative growth stage to the late stage of flower bud differentiation,the DNA methylation level of Rhododendron bud was increased at first and then decreased,then increased again.There were significant differences between treatment groups in terms of the DNA methylation level of Rhododendron bud.10.In the period of flower bud differentiation,both soluble sugar content and soluble protein content in the leaves were higher than the control groups.At the early stage of flower bud differentiation,carbohydrate content in the leaves reached it’s maximum,then decreased during bud differentiation period,finally increased again in the late stage of flower bud differentiation.There were significant group effects in terms of soluble sugar content and soluble protein content in the leaves(p<0.05).11.From the vegetative growth stage to the early stage of flower bud differentiation,the SOD content and POD activity of the treatment groups decreased first and then increased,the MDA content in leaves was less than the control groups.There were no significant differences between the treatment groups and the control groups in terms of variations of SOD activity,POD activity and MDA content.The SOD activity and POD activity in the treatment groups were higher than in the control groups,while the MDA content was on the contrary.The results suggested that 5-azaC treatments has a positive effect on the antioxidation of Rhododendron leaves,while a negative effect on the peroxidation of the membrane lipid and the aging of Rhododendron leaves.12.At the vegetative growth stage,the correlations among physiological indexes of the 150mg/L treatment group varied during the growth stage.For example,after 20 days of treatment,the level of DNA methylation was significantly correlated with the content of MDA,POD and SOD were also significantly correlated.After 40 days of treatment,the level of DNA methylation was significantly correlated with the POD activity,SOD activity,and content of MDA.POD and SOD,MDA content were also significantly correlated.After 60 days of treatment,the soluble protein content was significantly correlated with the POD activity.After 80 days of treatment,the level of DNA methylation was significantly correlated with the SOD activity and MDA content.After 100 days of treatment,the SOD activity was significantly correlated with the POD activity,MDA content,POD activity and MDA content were also significantly correlated(p<0.01).