Study Of CO Regulated Disease Resistance Through CGMP In Postharvest Jujube Fruits

In order to determine the role of cGMP in the induction process of disease resistance by CO,the physiological and biochemical defence reaction were analyzed in the jujube fruits by the method of postharvest pathology and biochemistry.On the basis of this,quantitative real-time PCR was used to study the expression changes of defense genes,and to reveal the relationship between CO and cGMP signal pathway at the level of molecular biology.In this experiment,the jujube fruits were averagely divided into four groups.Three groups of jujube fruits were fumigated with 10?mol/L CO for 2 h.After that,the two groups were respectively treated with 10?mol/L ODQ and 10?mol/L ODQ+5?mol/L 8-Br-cGMP.After treatment,spore suspensions?5?L,1?10⁵spore/mL?of Alternaria alternata were injected into each hole.The relative physiological and biochemical indicators and the expression of defense genes were measured regularly after inoculation.The main results of the research are as follows,?1?Compared to CO+ODQ,CO and CO+ODQ+8-Br-cGMP treatments inhibited the expansion of lesion diameter,and reduced the red index,decay incidence and weight loss of jujube fruits.In addition,CO can improve the firmness,soluble solids?TSS?and titratable acid?TA?contents of jujubes by cGMP signal in the early stage of storage,but the effect is not significant.?2?Compared to CO+ODQ,CO and CO+ODQ+8-Br-cGMP treatments induced the activities of PAL,C4H,4CL and CHS,and promoted the accumulation of total phenolic compounds,flavonoids and lignin in jujube fruits.Thus,CO can activate the phenylpropane metabolic pathway and enhance the disease resistance of the fruits by cGMP signal.?3?At the early stage of storage,CO can accelerate the production rate of O₂^·-and increase the content of H₂O₂ through cGMP signal.Meanwhile,the activities of NOX,SOD and POD were also accumulated,while the activity of CAT markedly decreased.Compared to CO+ODQ,CO and CO+ODQ+8-Br-cGMP treatments also increased the activity of APX and the contents of AsA and GSH.These results indicated that CO treatment could induce reactive oxygen metabolism in jujube fruits through cGMP signal,and inprove the disease resistance of the fruits.?4?Compared to CO+ODQ,the treatment of CO and CO+ODQ+8-Br-cGMP increased the ativities of PPO,CHT and GLU in jujube fruits inoculated with A.alternata,and reduced the occurence of postharvest diseases.?5?Through cGMP signal,CO can enhance the expression of PAL,PPO,SOD,POD,CHT and GLU genes and inhibit the expression of CAT gene in jujube fruits,which is corresponding to the changes in enzyme activities.In conclusion,CO treatment could induce the disease resistance and reduce the occurrence of postharvest diseases in jujube fruits through cGMP signal.The enhancement of disease resistance in fruits was closely related to the activation of phenylpropane metabolism,reactive oxygen metabolism,the induction of pathogenesis-related proteins and the expression of defense genes.