不同果肉质地枇杷果实发育过程中果胶代谢及相关基因表达分析

Pectin Metabolism and Related Gene Expressions during Loquat Fruit Development

【目的】研究红肉枇杷与白肉枇杷果实生长发育过程中果胶代谢和相关基因表达的动态规律,旨在探索枇杷果肉质地软化与果胶代谢的关系,为枇杷果肉品质改良、栽培选育等提供理论基础。【方法】以主栽红肉品种东湖早、早钟6号和白肉品种贵妃、白梨两类质地差异较大的果实为试材,测定不同发育时期的3种形态果胶含量以及果胶甲酯酶(Pectin methyl-esterase,PME)、多聚半乳糖醛酸酶(Polygalacturonase,PG)、果胶裂解酶(Pectate lyase,PL)、β-半乳糖苷酶(Beta-galactosidase,β-Gal)活性及其基因相对表达量。【结果】在果实发育后期,东湖早、早钟6号枇杷果实水溶性果胶(Water soluble pectin,WSP)含量显著低于贵妃、白梨,离子结合果胶(Ionic soluble pectin,ISP)及共价结合果胶(Covalent soluble pectin,CSP)含量差异不显著;PME活性随果实成熟软化先上升后下降,PG、β-Gal活性整体逐渐上升,且在果实发育后期,白肉枇杷果实PG、β-Gal活性显著高于红肉枇杷。相关基因表达量的变化趋势表现不同,白肉枇杷PL、PG、β-Gal基因相对表达量在果实成熟后期均显著高于红肉枇杷。【结论】果胶代谢参与了枇杷果实成熟软化进程,WSP含量、PG及β-Gal活性差异是导致枇杷果肉质地差异形成的生理因素;红肉枇杷和白肉枇杷果实成熟后期质地品质的差异可能是果胶降解相关基因相互协调作用的结果,其中PL、PG、β-Gal是关键基因。

【Objective】Pectin metabolism and related gene expressions during the fruit developments of red-flesh and whiteflesh loquats were studied to decipher the mechanism associated with the changes on pectin and difference on pulp texture.【Method】Loquat varieties bearing fruits with distinctive textural characteristics,namely,the red-fresh Donghuzao and Zaozhong 6 and the white-flesh Guifei and Baili,were used for the study.Contents of 3 forms of pectin,activities of related enzymes,and relative expressions of genes related to pectin methyl-esterase(PME),polygalacturonase(PG),pectate lyase(PL),andβ-galactosidase(β-Gal)in the fruits at development stages were determined.【Result】During the late stage of fruit development,the red-flesh loquats had a significantly lower water soluble pectin(WSP)content than the white-flesh fruits.But no significant difference on either ionic soluble pectin(ISP)or covalent soluble pectin(CSP)was observed.As the fruit was ripening and turning soft,the PME activity increased initially,then declined.Meanwhile,the activities of PG andβ-Gal rose continuously and were significantly higher in the white-flesh loquats than in the red-flesh fruits near the end.Approaching the final ripening process,the expressions of PL,PG,andβ-Gal in the white-flesh fruits were all significantly higher than those in the red-flesh ones.【Conclusion】The pectin metabolism directly involved in the ripening and softening process of loquat fruits.The WSP content as well as PG andβ-Gal activities physiologically governed the texture of loquat pulp.The concerted effect of the pectin degradation and the related genes determined the softening of loquat fruits.Among the genes,PL,PG,andβ-Gal might be the key genes that differentiated the texture of red-flesh and white-flesh loquats.