Studies On The Effect Of Exogenous Nitric Oxideon Photosynthetic Characteristics And Antioxidant Enzymes Activity Of Maize Seedlings Under Drought Stress

Drought is a key ecological factor that restricting the productin of food crops in our country.Photosynthesis is an important part in the process of plant life,and very sensitive response to drought stress.In order to explain the regulatory mechanism of exogenous nitric oxide on the photosynthesis characteristics and antioxidant enzyme system of maize?Zea mays L.?under drought stress,the hydroponic experiment was conducted in a growth chamber with the Zhuyu 309 as the material and researched the effects of exogenous NO on the chloroplast ultrastructure,photosynthetic characteristics,photosynthetic gene expression and activity of antioxidant enzymes and the influence of the isozyme expression of maize seedling leaves under drought stress,the main results were as follows: 1.Effects of exogenous NO on the leaf photosynthesis and the ultrastructure of chloroplasts in the leaves of maize seedlings under drought stressThe ultrastructure of chloroplast in the leaf became round and separated from the plasma membrane with the thylakoid lumen expansion,stacked pile of loose,granular osmiophilic increased clearly under drought stress.In addition,compared with control results,photosynthetic rate?Pn?,stomatal conductance?Gs?decreased significantly.The grana lamella gradually clear and granular osmiophilic decreased obviously with the treatment of exogenous NO.At the same time,PSII maximum photochemical efficiency?Fv/Fm?and PSII potential activity?Fv/Fo?were decreased under drought stress,however,the Fv/Fm and Fv/Fo were improved with the treatment of exogenous NO.The results suggested that the treatment of exogenous NO can relieve the inhibition the activity of PSII reaction center and maintain high PSII photochemical efficiency,indicating that NO plays a protective role to stabilize the structure and function of PSII reaction center.2.Effects of exogenous NO on the antioxidant enzymes and its isoenzymes in the leaves of maize seedlings under drought stressUnder drought stress,the CAT,POD of maize seedlings activity began to decline,but the SOD activity was increased,and the O₂^-and H₂O₂ content also were significantly raised compared with control results.However,with the treatment of NO and then drought stress,the enzyme activity and its isozymes had increased in varying degrees.Moreover,compared with the drought,O2-and H2O2 was reduced by 27.4% and 27.4%,respectively.The results show that the treatment of exogenous NO increased the antioxidant enzymes activity of maize seedling and reduced the accumulation of reactive oxygen species under drought stress.3.Effects of exogenous NO on the photosynthesis gene and Rubisco,RCA enzyme activity in the leaves of maize seedlings under drought stressThe genes of psb A,rbc L,rca and the enzyme activity of Rubisco and RCA from the maize seeding leaves were reduced significantly in the gene transcription level under drought stress.After exogenous NO pretreatment,the genes relative expression of psb A,rbc L,rca greatly were improved and the enzyme activity of Rubisco and RCA with exogenous NO treatment increased by 32.7% and 14.67%,respectively.However,the rbc S gene showed a significant increase in drought stress,with the treatment of NO and then drought stress rbc S gene increased 1.86 times.This results illustrated that the exogenous NO promoted the expression of photosynthetic gene and improved the enzyme activity of Rubisco and RCA.The findings of this study suggest that exogenous NO increased maize seedlings chloroplasts structure stability,improved the gene expression of psb A,rbc L,rbc S,rca and the enzyme activity of Rubisco and RCA that reduced the extent of the damage PSII reaction centers under drought stress,which help the maize seedling increased carbon assimilation capacity to maintain high photosynthetic rate and decreased the drought inhibition of photosynthesis of maize seedling.Exogenous NO improved the SOD,POD,CAT and its isozymes activities of maize seedling to enhance the ROS removal ability under drought stress,reduced the generation of active oxygen and other harmful substances for improving the drought resistance of maize.