The Study On Biochemical, Photosynthetic And Chlorophyll Fluorescence Characteristics Of Flag Leaf Of "Stay-green" Wheat After Florescence

As the most important food crop worldwide,wheat is regarded as a cereal with considerable potential to increase yield,particularly in marginal agricultural areas.The senescence of wheat leaves is accompanied by the grain filling process,k is a great significance to study the photosynthesis during the senescence of wheat leaves because it contributes greatly to grain yield.Leaves senescence during the grain-filling period causes a sharp decrease in wheat yield by shortening the duration of active photosynthesis. Senescence of flag leaf is effectively delayed in "stay-green" wheat cultivars afer Florescence.Much more photosynthates are synthesized for grain.Here we use the materials of"stay-green" wheat cultivars.We studied the changes of the biochemical,photosynthetic and chlorophyll fluorescence characteristics during the senescence period and explained mechanism of delaying senescence.Meanwhile,we analysed the correlation between the main biochemical traits,photosynthetic characteristics,chlorophyll fluorescence parameters and 1000-kernel weight.The results are shown as follow:1 The "stay green" materials maintained a high level of chlorophyll content throughout senescence stage,and long period of high level of chlorophyll content is the most important biochemical elements of delaying senescence.In this study showed that the soluble protein of the "stay green" materials higher than CK in the senescence stage,which suggests that the "stay green" materials senescence extent is slower than CK.2 The stay-green" wheat cultivars,compared with CK,had the higher activity of CAT, SOD;and the raise of MDA content was more slowly.It is showed that the "stay green" wheat(CN17&CN18) have a greater ability to remove O₂^- so as to lighten the contamination of the active oxygen during the senescence stage3 The stay-green" wheat cultivars,compared with CK,had the higher value of Pn,Gs and Tr.The results showed that the duration of high Pn value(Pn＞10) of the "stay green" wheat lasted 12 days longer than that of CK materials.The multiple linear regression and correlation analysis of Pn was studied,the results suggested that the decline of Pn mainly depended on the stomatal limitation in early period of senescence,but in the later period of senescence,it depended on the assimilation capacity of mesophyll cell.4 There was a degressive trend by the means of measuring the chlorophyll fluorescence parameter of the flag leaf in the senescence period.In later period of senescence,this study on the chlorophyll fluorescence parameter measurement of "stay-green" wheat cultivars showed that Fv/Fm,Fv'/Fm',ΦPSâ…¡,ETR and qP had the higher value than CK,indicating that the PSâ…¡of"stay-green" wheat were effectively protected so as to maintain the higher activity of biochemistry.5 We also detected a significant increase of NPQ in the in early period of senescence, which indicated that the mechanism of thermal dissipation had been started to dissipate excess lightenergy,and protect the flag leaf from photo-oxidation.But in the in later period of senescence,this study showed that NPQ had the higher value than CK,which indicated that the thermal dissipation depending on xanthophyll cycle was more efficient so as to dissipate excess lightenergy.6 It was showed that the trait of delaying senescence of "stay green"whaet had higher abilities to accumulate photosynthate so as to improve the yeid of the grain by the means of measuring the 1000-kernels weight of leaf-cutting treatment in n the later period of senescence.7 The conclusion was that there is significantly positive correlation by the means of analysing the correlation between chlorophyll fluorescence parameter and net photosynthesis rate.But the correlation between chlorophyll fluorescence parameter and Pn were declined as time extended under leave senescence period.8 The conclusion was that the 1000-kernels weight was significantly positive correlated to Fv/Fm,Fv'/Fm',ΦPSâ…¡,ETR qP and Pn by the means of analysing the correlation between chlorophyll fluorescence parameter,Pn,and 1000-kernels weight.But the value of correlation declined as time extended under leave senescence period.On the other hand, the 1000-kernels weight was significantly negative correlated to MAD at middle senescence stage and later senescence stage.