Physiological Traits Of Top-two Leaves Of Inverted Senescing Wheat Under Shade Stress Condition

The research was carried out at Water-saving&Irrigation Experiment Station inNorthwest A&F University in2011and2012.Shading experiments were designed accordingto low light intensity problem caused by the condition of rainy and little light in Huang-huaiwinter wheat region,Selected inverted senescing wheat Wenmai19、Yumai19, Lankao Aizao8and Shaan229upright stems as material,Which had same flowering period.simulated lowlight conditions by building shading shed in the late of wheat jointing until maturity. The aimof this study was to investigate the effects of low light on the chlorophyll content, leaf colorchanges, photosynthetic characteristics, chlorophyll fluorescence and activity of antioxidantenzymes and MDA content of top tow functional leaves of inverted senescing wheat.In orderto investigate the adaptability to the environment of inverted senescing wheat,to provide atheoretical basis for the identification and breeding of wheat.The results were as follows:1. Shading increased surface and deep water of soil,which would help to maintain andincrease the surface soil water content,but the shading was not conducive to the upwardmovement of deep water.In normal and shading conditions,leaf color inversion phenomenonappeared in the later stage of grain filling for inverted senescing wheat,but the inversion agingrate was significantly reduced by shading treatment for inverted senescing wheat,and theinversion rate was affected by varieties and age.The number of green leaves of inverted stemswere more than the upright stems,that is mean inverted senescing wheat leaves has a longerblades duration.The chlorophyll content of wheat each blade were increased in shadingcondition,and significantly delayed the degradation rate of chlorophyll and slowed down thewheat senescence rate.However,leaf color inversion phenomenon were delayed for invertedsenescing wheat,so that the degree of leaf color inversion phenomenon of inverted senescingwheat leaves were weaken2. Net photosynthetic rate (Pn) and stomatal conductance (Cs) of two functional leavesof Shaan229、Wenmai19and Lankaoaizao8in Long-term shading conditions weresignificantly lower than those in normal conditions during the whole growth period; Shadingdelayed the net photosynthetic rate (Pn) and stomatal conductance (Cs) maximum anddownhill period of function leaves,while reduced transpiration rate (Tr) of function leaves, but decreased to a lesser extent;Shading decreased net photosynthetic rate (Pn)、stomatalconductance (Cs) and transpiration rate (Tr) of function leaves less than the control during thewhole growth period, slowed down the aging rate of inverted senescing wheat,and made leafcolor inversion phenomenon of net photosynthetic rate (Pn)、transpiration rate (Tr) andstomatal conductance (Cs) of flag leaves and second leaves later, so that the invertedintensity was significantly lower than that in normal conditions.3. The shading made actual photochemical efficiency value (ΦPSⅡ）of wheat increasingduring the whole growth period,improved the Fv/Fm value and Fv/F0value of later fillingstage, reduced the value of F0/Fm, significantly delayed aging rate of Leaf-color inversionwheat.The actual photochemical efficiency（ΦPSⅡ）decreased by a low speed with a smalldeclining for two functional leaves of four varieties wheat during the whole growth period inShading treatment conditions, at the same time, shading delayed downhill period of Fv/F0value,and delayed the time that leaf color inversion appeared for ΦPSⅡ、Fv/Fm、Fv/F0andF0/Fm values,so that the leaf color inversion intensity were weaken.4. Shading made MDA content lower than that in the normal conditions,Which inhibitedthe CAT activity at the early of flowering,and improved the POD activity of the whole growthperiod.Postponed the maximum time and downhill period of the CAT and POD.However,theactive oxygen in the body removed mainly through the POD at the early of flowering.Afterflowering in late,CAT began to play a leading role. Shading pushed back the leaf-colorinversion time of CAT、POD and MDA content,and the leaf-color inversion intensity wereweaken.