Effect Of High Ozone Plus Temperature And Light Stress On Photosynthetic Characteristics Of Grape Leaves

With the increase of industrial exhaust gas and automobile exhaust emissions,the concentration of O₃ is increasing,and the ozone stress has become one of the environmental indicators that threaten crop yield and quality.The damage caused by the photooxidation of ozone under the strong light is more serious to the sensitive crops such as grape.During the growing season,grapes usually face O₃,strong light and high temperature stress,which can cause photoinhibition of photosynthesis and even cause irreversible damage of photosynthetic apparatus.However,the mechanism of the effect of ozone combined with high temperature and strong light stress on the photosynthetic characteristics of grape leaves is unclear.Therefore,there was a obvious academic value to study the mechanism of the stress caused by the combination of ozone,light and high temperature.There was an important practical significance to study the mitigation strategies.In this paper,the susceptibility of five grape varieties to ozone in the field and the anatomical differences of the leaves damaged by ozone were studied.The response of photosystem II activity to ozone stress under strong light and high temperature was analyzed,and the effect of MT（melatonin）on ozone stress of Cabernet Sauvignon（Vitis vinifera cv.Cabernet Sauvigon）was also studied.The main results were as follows:（1）Long term low concentration of O₃ stress led to severe photoinhibition in leaves of susceptible grape varieties in the vineyard environment,the order of five varieties to ozone is FR 177-67>Becker Hance>Frontnac>Red Globe>Moldova.Under a long period of low concentration of O₃ stress,the net photosynthetic rate of symptomatic leaves of the five varieties decreased significantly from 50%to 30%compared with those normal controls,and the content of chlorophyll a decreased significantly from 56%to 37%.（2）Under a long period of low concentration of O₃ stress and photooxidation stress,the leaf tissue structure and chloroplast ultrastructure of Becker Hance which is an ozone sensitive grape variety were seriously injured.The number of apparent brown spots increased and the phenomenon of dehydration and desiccation occurred increase severity of the injury;the inner gap of leaves cells increased gradually,the cell wall of mesophyll cells became thinner,and the inner membrane system disintegrated;chloroplast reduced and deformed,chloroplast membrane began to dissolve,and the number of chloroplast,chloroplast grana andgrana layer gradually decreased.（3）The study of showed,Logistic regression analysis was performed to examine the associations among O₃ concentration（A）,light intensity（B）and Fv/Fm.The resulting regression equation was:Y=+0.73-0.034*A-0.022*B-0.018*A*B-5.162E-003*A2+8.375E-004*B2.At a light intensity of 1222.93 μmol·m^-2·s-1 and O₃ concentration of 117.43 nL/L,Fv/Fm was 0.711（0.711 was found to be the critical value ofFv/Fm for leaves）.Fv/Fm values were then found to increase at a stable light intensity of 1222.93 μmol·m^-2·s-1 with decreasing ozone concentration,and at a stable O₃ concentration of 117.43 nL/L with increasing light intensity.（4）The study of three factrs of ozone,high temperature and strong light showed that,Strong light(1600 μmιl·m^-2·s-1)and high temperature（40°C）increased the damage of PSII under O₃ stress(120 ±20 nL·L^-1).The maximum value of Fv/Fm and the electron transfer rate ETR decreased by 10.3%and 17.6%respectively under 40°C,the effect of strong light intensity was more significant,Fv/Fm and ETR decreased by 38.8%and 37.5%,respectively;when strong light intensity and high temperature were present at the same time,PSII damage was most obviously damaged under O₃ stress,Fv/Fm and ETR decreased by 54.8%and 62.5%respectively.（5）The plants’ growth inhibittion caused by ozone stress(120 nL · L^-1)were relieved by 100 nmol-L^-1 of melatonin application for 6 times.The decrease of photosynthetic pigment content and Fv/Fm was slowed down,the degree of inhibition of electron transport and PS Ⅱ activity was alleviated,the protection mechanism was improved,and leaf photosynthetic function was protected.Compared with O₃ stress,the Pn was increased by 133.3%and chlorophyll a and chlorophyll b were increased by 14.4%and 10.6%respectively after the application of melatonin.