| Fruit softening is a significant event during ripening and has been widely accepted to be the result of the alteration of cell wall components. Studies on two peach cultivars:’Yuhuasanhao’and’Jianayan’showed differences in softening behavior. Each cultivar showed a unique relationship between softening, ethylene production and respiration rate. The changes of physiological, the cell wall ultrastructure in the flesh cells, the degradation characteristics of cell wall polysaccharides as well as correlative glycosidaes for cell wall polysaccharides degration during peach fruit ripening and softening were studied, providing some theoretical basis for further study the role of cell wall changes in stone hard fruit ripening and softening. The main results were as follows:The modification of firmness, ethylene production and the ultrastructural change in the flesh cells were determined in present study. The results preliminary showed that, respiration rate and ethylene production increased significantly in’Yuhuasanhao’accompanied by the decline of firmness, while relatively higher firmness had been remained during’Jianayan’peach fruit ripening and the firmness decreased little in the end of postharvest storage. The ethylene production in’Jianayan’peach fruit was less than1%of that in’Yuhuasanhao’peach fruit. The results of cell wall ultrastructure showed that the cell wall degradation in ’Yuhuasanhao’peach fruit launched earlier than’Jianayan’peach fruit. A significant change in ’Yuhuasanhao’cell wall was observed in the early stage of postharvest storage.The results for cell wall polysaccharides showed that the content of CDTA-1pectin polysaccharide increased while the content of Na2CO3-1, Na2CO3-2pectin polysaccharide, KOH-1and KOH-2hemicellulosic polysaccharides and CWM-residue polysaccharide decreased during peach ripening and softening. However, the rate of decline in’Yuhuasanhao’was faster than in’Jianayan’. That may contribute to the process of fruit softening, indicating that pectin experienced degradation and tightly covalently bound pectin transformed into ion bound pectin. However, the degradation rates of cell wall polysaccharides differed significantly in the two different types of peach fruit.High performance liquid chromatography was used to determine molecular weight distribution in cell wall polysaccharides. The results showed that the molecular mass distributions of CDTA, Na2CCO3and KOH fractions exhibited downshift tendency in both of two types of peach fruit, indicating that cell wall polysaccharides occurred depolymerization and high molecular weight materials changed to the low molecular weight substances during peach fruit ripening. But the molecular weight, the content and the time of depolymerization in polysaccharide components between the two cultivars showed a significant difference, indicating that the pattern of depolymerization had some influence on the peach fruit softening.Monosaccharide compositions of cell wall polysaccharides were determined by gas chromatography. The results showed that pectic polysaccharides depolymerized, the pectic main chains that riched in galacturonic acid took rupture along with the degradation of galacturonic acid residues and the loss of arabinosyl and galactosyl residues from pectic side chains. The loss of arabinosyl and galactosyl residues also showed in hemicellulosic polysaccharides. The difference between the two cultivars was the initial time of degradation which means that the melting-flesh peach fruit’Yuhuasanhao’was in the front of the ripening while the non-melting-flesh fruit’Jianayan’was in the later of the ripening. And branched-chain galactose degraded mainly in the period of pre-softening, while branched-chain arabinose degraded mainly in the period of rapid softeningChanges of correlative glycosidase for the degradation of cell wall polysaccharides were analyzed during the ripening of peach fruit. The results showed that P-galactosidase gene expression and activity had a higher level in the early stage of softening and it may contribute to softening initiation. The gene expression and activity of a-L-arabinofuranosidase were higher in the late ripening, which were closely related with fruit fast softening. The change of a-L-arabinofuranosidase slightly lagged behind the rapid changes of ethylene and ethylene synthetic enzymes, indicating that the enzyme activation was closely related with accumulation of the endogenous ethylene and had more remarkably effect on peach mid to later fast-softening. At the same time, a-L-arabinofuranosidase protein accumulation and activity as well as gene expression had a good correlation with fruit softening. This is the further evidence for the effect of a-L-arabinofuranosidase on peach fruit softening.1-MCP effectively delayed the decline of peach fruit firmness and also delayed the increase of endogenous ethylene production and respiration rate, which made the cell wall of pulp maintain its integrity for a longer time. But the time of1-MCP effect during storage differed to some extent between the two different cultivar. The inhibitory effect of1-MCP on’Yuhuasanhao’ was in the early to mid-term storage, while the effect on ’Jianayan’was in the late storage. a-L-Arabinofuranosidase translation, protein accumulation and enzyme activity were inhibited accompanied with the postpone of peach fruit softening. That further proved that the role of a-L-arabinofuranosidase on the degradation of cell wall was regulated by ethylene. |
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