Study On Regulation Leaves Senescence With Nitrogen Levels In Sugar Beet (Beta Vulgaris L.)

By using diplontic main plant varieties Tianyan7,Tianyan8 and KWS3418 and combining the methods of pot planting and field trial,the experiment setted N₀,N₆₀,N₁₂₀ N₁₈₀,N₂₄₀ five nitrogen levels,researched senescence-associated physiological indexes of main leaves and whole sugar beet plant.Regulation leaves senescence with nitrogen nutrition in sugar beet was preliminarily discussed.The results showed that:1 Low nitrogen stress-induced the premature Senescence of sugar beet leaves,It manifested as the total sugar beet green leaves reduced and leaf life shortened.Viewing the physiological characteristics of the Fifth,tenth,fifteenth leaf of sugar beet,low nitrogen induced the whole plant senescence,an appropriate amount of nitrogen fertilizer could delay functioning leaf senescence.2 Comparising the leaf life of the three sugar beet varieties,the general result is that: KWS3418＞Tianyan8＞Tianyan7.The 20～25 leaf had the longest leaf life. 54.5～62.5 days for Tianyan7,55.6～64.5 days for Tianyan8,and 58.1～70.4 days for KWS3418.3 Regardless of the single leaf or whole sugar beet plant,the content of Chlorophyll and RuBPase both showed single-peak curve,and had the same peak period.Different nitrogen levels regulate senescence process by senescence-associated physiological indexes.the general result is that the higher nitrogen levels,the higher chlorophyll content and RuBPase activity.4 With the different conditions of nitrogen,the GSA of different sugar beet varieties showed single-peak curve in each growing stage,the peak appears in the early July.With the nitrogen raising,the GSA increased in different growing stage.5 The changes of activity of protective enzymes(SOD,POD) showed single-peak curve on the growth and development of sugar beet,the period of SOD activity-peak was earlier than POD.The activity of SOD and POD rised as the increased level of nitrogen,when the amount of nitrogen application was higher than 120 kg/hm²,the increase of protective enzymes showed insignificant.It showed that sufficient nitrogen suppliment was benefit to hold a higher level activities of protective enzymes,the removal of oxygen free radical which from the aging process could delay leaf senescence. 6 The content of MDA rised as the growth and development of sugar beet.The content of MDA under different application of nitrogen were as follows:N₀＞N₆₀＞N₁₂₀＞N₁₈₀＞N₂₄₀.In the period of seedling and phyllome formation,the content of MDA was lower and the changes were relatively steady,In the period of tuber rise and sugar accumulation,the degree of leaf senescence deepen with nitrogen nutrition stress aggravating,the content of MDA of beet leaf in all treatments showed a trend of rapid increase.7 The concent of chlorophyll showed a significantly positive correlation with Rubp-carboxylase,r-value is 0.8859**.R-values(0.8905*,0.8039*) were showed a significantly positive correlation with GSA and SOD respectively.GSA and Rubp-carboxylase are the key enzymes in nitrogen and sugar metabolism of sugarbeet.there are high significant positive correlation between them.Relation coefficient is 0.7708*.In the aging process of sugarbeet,SOD and POD play a coordinating part which could remove the inner reactive oxygen species,there also had high significant positive correlation between them,relation coefficient is 0.9289**.8 The order of the effect on yield at different nitrogen levels was: N₁₈₀＞N₁₂₀＞N₂₄₀＞N₆₀＞N₀;The effect on sugar content was in the order:N₀＞N₆₀＞N₁₂₀ N₁₈₀＞N₂₄₀.The effect on sugar yield was in the order:N₁₂₀＞N₁₈₀＞N₆₀ N₂₄₀＞N₆₀.9 The content of Chlorophyll,RuBPase and SOD showed single-peak curve,and had the same peak period.The change of this three indexes fully showed growth and development process of the leaf senescence,could be used to predict leaf senescence of sugar beet.