Changes In Physical Structure And Chemical Composition Of Cutin Of Pingguoli Pear And Their Effect On Alternaria Alternata Infection

Cutin of fruit, as the first barrier against pathogen infection, plays an important role inhost-pathogen recognizing and attacking host. Our previous results showed that surfacestructure of Pingguoli pear influenced the infection process of Alternatia alternata. On thebasis of our previous studies, changes in physical structure and chemical composition of cutinof Pingguoli pear will be observed or analysized systematically by scanning electronmicroscope (SEM), transmission electron microscopy (TEM) or gas chromatography–massspectrometry (GC-MS); in addition, regulatoray effect of changes in physical structure andchemical composition of cuitin on A. alternata growth and infection was also studied, andpreliminary analysis correlation coefficients of water loss rate and cutin monomer. The resultsshowed as follows:1. Cuticle physical structure presented significant change during Pingguoli developmentand storage. At30days after full bloom (DAFB), cuticle layer was thin and distribute uneven;cuticle layer became integraty gradually and preliminary form subepidermal cuticular depositat60DAFB; after80~100DAFB, the internal cuticle keratin deposition and further formkeratin plug; at the end of development period(130d), cuticle layer covered with a waxycrystals. During cold storage, the internal cuticle keratin deposition further accumulation,form clear keratin plug, at the end of storge period(200d), the waxy layer of fruit covered withlarge pieces of crystals.2. Chemical composition of cuitin also changed during Pingguoli development andstorage. Fatty acids, dual carboxyl acid,alkanes, alcohols and aldehyde were detected in cutinextrcts during development. The predorminant compound was fatty acids, with thedevelopment prolonging, its content increased, at the end of development period(130d)，thecontent was up to275ug/cm2. Carbon chain length of cutin compounds was C9～C24，andshowed even chain advantage. C16, C18, C20, C22were abundant, the highest content wasC18. With development prolonging, the content of C16、C18increased, while the content ofC22decreased. The main monomer substances are10,16-dihydroxy hexadecanoic acid、9,10,18-trihydroxy octadecanoic acid and docosadienoic acid. With development prolonging，thecontent of10,16-dihydroxy hexadecanoic acid、9,10,18-trihydroxy octadecanoic acidincreased, while the content of docosadienoic acid decreased. During Pingguoli development，the saturation of the fatty acids also changed with development prolonging，the content ofsaturated fatty acids increased，while the Content of unsaturated fatty acids decreased. Fatty acids, dual carboxyl acid and alkanes were detected during storge. The predorminantcompoud was also fatty acids, with the storge prolonging, its content increased, at the end ofstorge period (200d)，the content was up to495ug/cm-2. With the development prolonging, thecontent of the main monomer substances,10,16-dihydroxy hexadecanoic acid,9,10,18-trihydroxy octadecanoic acid,9,10-epoxy-18-hydroxyl octadecanoic acid and18-hydroxyl9-octdecenoic acid wre presented increasing trend. During storge period, chemicalcomposition of carbon chain length distribution was the same as development period.3. Cutin extracts have some inhibitory effect on mycelium growth and sporegermination of A. alternata, but there was no obvious regularity. Cutinase produced during A.alternata infection in Pingguoli pear, and the most activity of cutinase appeared at4days afterinoculation, enzyme activity was up to10u/ml at8days. chemical composition of cuticle alsoinduced cutinase.4. With the development and storge prolonging, water loss rate of Pingguoli fruitdecreased, and there were significant positive correlation between water loss rate and22:02,significant negative correlation between water loss rate and C18, Epoxy w-OH, negativecorrelation between water loss rate and16:0Di-OH,18:0Tri-OH and16:0w-OH.In summary, both composition and morphology of cuticular cutin of Pingguoli pear fruitare changed during development and storge period, thereby affecting the behavior of A.alternata infection and fruit water loss rate, however specific regulation mechanism needsfurther study.