Role Of Phenols And Enzymes In Phenylpropanoid Pathway In Apple Fruit Resistance To Botrytis Cinerea

Apple fruits are rich in phenolic compounds that may enhance resistance to grey mould disease caused by Botrytis cinerea.Using apple?Malus domestica Borkh.?cultivars Fuji and Qinguan,we analyzed the contents of total phenols,total flavonoids,eight individual phenolic compounds in the flesh and ten individual phenols in the peel as well as H₂O₂,O₂·^-and the activities of key enzymes in the phenylpropanoid pathway in the flesh of control and B.cinerea-inoculated fruits.This research may be useful for characterizing the mechanism?s?underlying plant resistance to B.cinerea,with potential implications for the screening of grey mould disease-resistant apple varieties in breeding programmes.The main results are as follows:1.Chlorogenic acid,ferulic aicd,gallic acid,quercetin,phlorizin,catechin and epicatechin all can be determined in‘Qinguan'and‘Fuji'apple flesh.Chlorogenic acid content in‘Qinguan'apple flesh is significantly higher than in‘Fuji',while the content of catechin and epicatechin are significant higher in‘Fuji'than in‘Qinguan'.Apple peels also rich in phenols.Quercetin-3-galactoside is the most important phenol in the peel of‘Fuji'apple,whereas chlorogenic acid is the most important phenol in the peel of‘Qinguan'apple.Moreover,flavanols and scabiolide-3-galactoside are also the primary phenols in apple peel of both cultivars.The contents of all individual phenols except gallic acid tested in the present study in apple peel are significantly different between‘Qinguan'and‘Fuji'.2.After infected by B.cinerea,phenols in apple flesh of‘Qinguan'and‘Fuji'changed significantly,especially chlorogenic acid and ferulic acid.The content of chlorogenic acid decreased significantly in‘Fuji',while significant increase of chlorogenic acid content was observed in‘Qinguan'.Moreover,ferulic acid content in‘Qinguan'increased significantly,whereas the content of ferulic acid showed no difference.And the other phenols tested in the present study showed no significant changes.3.After infected by B.cinerea,phenols in apple peel of‘Qinguan'and‘Fuji'changed significantly.Chlorogenic acid increased significantly in the peel of Qinguan apple,but decreased in the peel of‘Fuji'apple.Flavanols including catechin,epicatechin,proanthocyanidin were induced in both‘Fuji'and‘Qinguan'cultivars after infection.Significant decreases of flavanols contents were observed in Fuji fruit,while there is no significant changes in Qinguan fruit.4.PAL,C4H,4CL and CAD in Phenylpropanoid pathway changed significantly in the defense reactions of apple fruits to grey mould.The activities of PAL and 4CL were significantly induced in both cultivars,however,the changes of PAL and 4CL in‘Qinguan'apple were much obvious than‘Fuji'.C4H and CAD activities in‘Qinguan'also increased significantly while in‘Fuji'decreased significantly.‘Qinguan'fruit synthesized more phenols after infection which slows down the development of grey mould disease.5.Content of ROS changed significantly in both apple cultivars after infection.Peak of H₂O₂ content was observed in both cultivars,while the peak in Fuji apple is much smaller.And a peak of O₂·^-content was observed in both cultivar,whereas high level of O₂·^-content was maintained for a long time,which may cause damage to the host cell.