Effects Of Exogenous Nitric Oxide(NO) On Drought Tolerance And Signal Response Of Blueberry Seedlings

Blueberry is a plant with shallow root system,with thin and underdeveloped roots,insignificant taproots and no root hairs,which cannot absorb water in deep soil.Therefore,blueberry has strict requirements on soil water and is vulnerable to drought stress.As an important foreign signaling molecule,NO is used to protect plants from biological and abiotic stress induced damage.At present,the research on NO production and signal transduction in plants has been widely concerned and developed rapidly.The effects of different concentrations of exogenous NO on the physiological characteristics of blueberry leaves and the signal transduction of NO under moderate drought stress were investigated by using two-year-old blueberry’Lanfeng’as experimental material.The experimental treatments were as follows:CK1:normal water supply（soil moisture content was 70%～80%of the maximum field water capacity）+distilled water;CK2:moderate drought stress（45%～55%of maximum soil water capacity）+distilled water;T1:moderate drought stress+100μmol·L^-1SNP;T2:moderate drought stress+200μmol·L^-1SNP;T3:moderate drought stress+300μmol·L^-1SNP;T4:moderate drought stress+400μmol·L^-1SNP;T5:Moderate drought stress+500μmol·L^-1SNP.Samples were taken at 0,3,6,9 and 12 days of drought stress treatment to determine various physiological indexes.The main results are as follows:1.Effects of different treatments on photosynthetic characteristics and chlorophyll fluorescence characteristics of blueberry leaves:Under drought stress,the photosystem was damaged,and exogenous NO could alleviate the damage to the photosystem.The results showed that the decrease of Pn under drought stress was affected by non-stomatal restriction,and the application of exogenous NO maintained high Gs by adjusting stomatal opening and closing.It can slow down the degradation of Chl,increase photosynthetic electron transfer and maintain higher photophoto II activity,and protect the photosystem photophoto II activity under drought stress.Among them,at the 9th days of drought stress,T4(moderate drought stress+400μmol·L^-1SNP),the proportion of chl,RWC,Pn,Tr,Gs,Fm andФPSII increased by 50.00%,16.74%,69.55%,85.09%,57.32%,12.86%and 44.68%;Ci,Fo and Fv/Fm decreased by14.29%,27.72%and 10.11%,respectively.2.Effects of different treatments on physiological indexes of blueberry leaves:The superoxide dismutase（SOD）activity,soluble sugar（SS）content,proline（Pro）content,peroxidase（POD）activity and soluble protein（SP）content of blueberry leaves showed a gradual increasing trend with the extension of drought stress time.While malondialdehyde（MDA）content,membrane permeability,hydrogen peroxide（H₂O₂）content and superoxide anion radical(O₂^·-)production rate decreased gradually.On the 9th day of stress,the contents of SS,SP,Pro,SOD and POD activities of exogenous NO treatment groups reached the maximum values,and the best effect of T4 treatment was significantly higher than the rest of the treatment groups,which were 1.88%,1.72 mg/g,55.40μg/g,508.10 U/g and 12.19 U/g,respectively.MDA content,EC,H₂O₂content and O₂^·-production rate all decreased to the lowest levels,which were 86.62μmol/g,33.54%,8.37μmol/g,and 0.64μmol/（g·min）,respectively.3.Principal component analysis was used to process and analyze various physiological indexes,and the sequence of drought resistance of exogenous SNP with different concentrations was 400μmol·L^-1>300μmol·L^-1>500μmol·L^-1>200μmol·L^-1>100μmol·L^-1.Exogenous NO had a significant concentration effect on the alleviation of moderate drought stress in blueberry,whereby,400μmol·L^-1of SNP was the most effective.4.Signal response of NO to moderate drought stress in blueberry leaves:Ca²⁺,ABA,c GMP,PLD and MAPK responded positively to drought stress.On the 9th day of moderate drought stress,ABA content,Ca²⁺concentration,c GMP concentration and PLD activity of CK2 in drought treatment group were increased by 0.30μg/g,0.87 mmol/gprot,17.90 nmol/L and 7.83U/m L,respectively,compared with CK1.MAPK activity decreased by 5.57 U/L.Under moderate drought stress,the signal response of NO in blueberry leaves was related to ABA,Ca²⁺,c GMP,PLD and MAPK.