嘎拉苹果果实质地发育软化与细胞壁降解及其基因表达的关系

Correlation of Fruit Texture Development and Softening with Cell Wall Degradation and Related Gene Expression in Gala Apples

以嘎拉苹果为试材,分析了果实发育软化过程细胞壁组分、细胞壁酶活性及其酶基因表达的变化。结果表明,发育期,细胞壁物质(CWM)及其组分均先升后降,果胶中共价结合果胶(CSP)含量最高,纤维素含量远高于半纤维素,此期CSP和纤维素含量与硬度显著相关,细胞壁酶表现不同的活性变化和基因表达,并与细胞壁组分存在一定相关性,表明细胞壁降解参与了果实发育期的相关生理过程。采后CSP含量快速降低,水溶性果胶(WSP)含量开始增加,纤维素和半纤维素含量降低,均与硬度显著或极显著相关;细胞壁酶中,β-Gal活性和基因表达量增幅最快,α-Af和PG次之,PME活性和基因表达的增加时期相对滞后,且β-Gal和α-Af活性与硬度和各细胞壁组分的相关性强于PG和PME,PG与CSP和半纤维素表现较强相关性,而在PME上的相关性最差,说明细胞壁代谢与嘎拉果实软化密切相关,β-Gal和α-Af可能对果实软化的作用更强。

Changes in cell wall composition, enzyme activity, and gene expression during development and softening of Gala apples was investigated to identify correlations. The results indicated that the content and composition of cell wall material(CWM) showed a dynamic trend during development. Covalent soluble pectin(CSP) showed the highest content among the three pectins assessed and cellulose content was always significantly higher than that of hemicellulose. Firmness correlated significantly with CSP and hemicellulose content. Additionally, changes were noted in the activity and gene expression of cell wall enzymes during this stage, showing that cell wall degradation was involved in the physiological process of fruit development. After harvest, CSP content decreased rapidly with softening, water soluble pectin(WSP) content began to increase, while cellulose and hemicellulose contents decreased, all of which, correlated significantly with firmness loss. Among the cell wall enzymes, β-galactosidase(β-Gal) activity and Md Gal gene expression increased most rapidly, followed by that of α-Arabinofuranosidase(α-Af) and PG polygalacturonase(PG), while pectin methylesterase(PME) activity and Md PME increased at a later stage. Moreover, correlation with firmness and cell wall components was stronger for β-Gal and α-Af than that for PG and PME. PG activity correlated strongly with CSP and hemicellulose content, while PME activity showed the least correlation with changes in cell wall components. This indicated that cell wall metabolism had a close relationship with texture softening of ‘Gala' apple, and both, β-Gal and α-Af may play relatively more important roles in fruit softening.