Effect And Physiological Mechanism Of Different Light Qualities On Improving Low Temperature Light Inhibition In Peach Trees

When peach trees grow in the open air,they often encounter the cold spring when they blossom,sprout or spread their leaves.The temperature drops quickly and greatly during this period,and the low temperature lasts for a long time,the tree is very vulnerable to low temperature and weak light damage,even in the greenhouse environment will also appear low temperature,and even“Temperature inversion”phenomenon,so that the photosynthesis of peach tree has been affected,even produce the phenomenon of photoinhibition.Therefore,it is of great significance to improve the photoinhibition in low temperature and low light environment for both open-air and facility production of horticultural crops.It was found that the net photosynthetic rate（Pn）of nectarine leaves was significantly increased after supplemented with blue light and UV-B in the greenhouse.In this experiment,First,the3-year-old’Luyou No.3’（Prunus persica var.nectariana cv.Luyou3）peach tree is placed in the open air environment covered with shed film,performed the exposure of the blue light and UV-B.Determine the photosynthetic parameters of leaves from March to June;another,In the growth chamber,4℃and 100μmol.m^-2.s^-1 were set to simulate the cold spring cold（with normal temperature and light as a control）.Put peach tree in it.Spray a certain concentration of D1 protein synthesis inhibitor streptomycin sulfate（SM）and electron transport inhibitor（DCMU）.And supplemented with UV-B and blue light at 4℃low temperature.By measuring the photosynthetic parameters,fluorescence parameters,fast chlorophyll fluorescence kinetic curves,activity of PSⅠ and PSⅡ,antioxidant enzyme activity,MDA content,relative conductivity and chlorophyll content.To explore the improvement effect and possible mechanism of blue light and UV-B on the photosynthetic performance under low temperature and low light light inhibition,to provide theoretical basis and production guidance for the improvement of light inhibition and the rational application of light quality.The results were as follows:1.Under low temperature and low light stress,the PSⅠ activity of peach leaves was not damaged,but the PSⅡ activity decreased significantly,and the photoinhibition occurred.At the same time,ΦPSⅡ,ETR,q P and other PSⅡ fluorescence related indexes were significantly lower than those of the control group at room temperature,and the relative values of the rapid chlorophyll fluorescence kinetic curve（OJIP）was significantly decreased.2.There is a protective mechanism between the two photosystems under low temperature and weak light.Low temperature and weak light affects the synthesis and turnover of D1protein to reducing the activity and photosynthetic capacity of PSⅡ,while the photosystem protects the activity of PSⅠ from significant harm by reducing the electron transfer from the PSⅡ reaction center to PSⅠ.SM treatment and DCMU treatment significantly affected the activity of PSⅡ,but not the activity of PSⅠ.Spraying SM solution on the basis of low-temperature and low-light treatment resulted in significant decrease of the fluorescence indexes of PSⅡ,such as Fv/Fm,ΦPSⅡ,ETR,q P,etc.,however,there was no significant change in PSⅠ activity.SM inhibited D1 protein synthesis and turnover,which aggravated PSⅡ injury in leaves,but did not affect PSⅠ significantly.SM inhibited D1 protein synthesis and turnover,which aggravated PSⅡ injury in leaves,but did not affect PSⅠ significantly.Then we used DCMU to suppress the electron transfer between PSⅡ and PSⅠ,and found that Fv/Fm,ΦPSⅡ,ETR,q P and other indexes of PSⅡ decreased significantly,and the higher the concentration,the greater the decrease,but there was no significant change in PSⅠ activity.3.Blue light and UV-B enhanced the photosynthetic parameters of peach trees from March to June.Blue light and UV-B can effectively alleviate the low temperature and weak light caused by the phenomenon of peach photoinhibition.Blue light and UV-B irradiation increased the activity of PSⅠ slightly,but there was no significant difference compared with the control group,the photosynthetic pigment content and photosynthetic rate were significantly increased.The activities of SOD,POD and CAT were increased,the content of MDA and relative conductivity were decreased,and the resistance of leaves was increased.4.Adding blue light and UV-B to the normal light dose in the open air can effectively alleviate the low temperature light inhibition of peach trees,and the cost and effect are comparable.Considering that improper UV-B supplement is easy to cause damage to the leaves,it is suggested that the use of blue light be promoted in production.