Study On The Response Mechanism Of Pear Fruit Callus To Infection Of Scab

Infected by pathogens,plants will develop a series of responses to protect themselves against pathogens.The responses contain changes in plant tissue structure,resistant substances and generation of signal substances.The plants' own disease prevention and defense mechanism would be investigated through these changes and the relationship between each other.Pear scab is one of the main diseases in the production of pear trees,which is common in the pear area of north and south China.The research on scab has been carried out for many years,but this research on its own disease prevention and defense response after infection was not enough actually.In this study,the callus induced by resistant cultivar 'Huangguan' pear,moderately susceptible cultivar'Suli'pear and susceptible cultivar 'Xuehua' pear was used as experimental material.It revealed the mechanism of interaction between pear callus and pathogens from different perspectives through studying these changes of morphological structure,disease resistance substances and signal transduction after infection.The experiment laid the foundation for the study of the defense mechanism of host on pathogens.The main results of this study were as follows:1.The fruits of 'Huangguan' pear,'Suli' pear and 'Xuehua' pear were used as explants.The suitable medium was selected to induce callus and the callus was used as experiment material after subculture.The susceptibility and susceptibility index of different varieties of pear fruit callus were compared with those of different cultivars,and it behaved same.The results showed that it is feasible to investigate the defense mechanism with the pear callus as the material.2.Observing the pear callus's organizing feature infected by scab,we found the cell wall was degraded in the susceptible cultivar 'Xuehua' pear,and the conidia was completely inside the callus.Finally,there were little complete cells in sight.The superficial cells were destroyed and the contents of the cells were lost in the moderately susceptible cultivar 'suli' pear,while the cells inside the callus were relatively complete.Scab can only grew on the surface of'Huangguan' pear.The conidia cannot go into the tissue,so the cell wall was complete.3.The activity of POD,SOD and CAT began to increase when the callus was infected by scab.They changed collaboratively to scavenge active oxygen in the plants.At the early stage of infection,the activity and elevation of POD and CAT in the resistant cultivar were higher than those of the susceptible cultivar,and the activity of SOD was slightly lower than that of the susceptible cultivar.The three protective enzyme activities of resistant cultivars had been in a high level in the experiment,significantly higher than susceptible varieties.The activity of PPO in the resistant cultivar was significantly higher than that of the susceptible in the whole process of infection.The rising speed of PAL activity was faster and the activity was higher than that of the susceptible cultivar.The activity of protective enzymes and defensive enzymes in the callus of resistant cultivar was consistent with the ability of anti-scab.The isozymes of the resistant cultivar were highly expressed and produced new types.It indicated that the protective and defense enzymes play an important role in the resistance to the infection of scab.4.The pear callus was used as material to separate and purify protoplasts through enzymatic hydrolysis and suspension methods.We found that the effect of 2%cellulase + 0.5%pectinase was better and the removal rate of the wall was higher.Meanwhile,we found the number and activity of protoplasts were higher using 1.5mol/L sucrose solution and 100×g centrifugal speed to separate and collect them.5.The concentration of Ca2+ in cytoplasm increased rapidly and peaked at 30 min after infection,and the concentration of the resistant cultivar was significantly higher than the susceptible cultivar.Then the concentration began to decrease.The descent speed of the susceptible cultivar was slower than that of the resistant cultivar.