Cell wall metabolism and related gene expression in Malus domestica Borkh. during fruit growth and softening

Introduction. Pre-harvest fruit development of apple can have a great effect on its storable quality. However, little research has focused on fruit metabolism during growth. Our objective was to study cell wall metabolism during the various stages of fruit growth and softening to gain more insight into the nature of fruit development and ripening. Materials and methods. Apple varieties Fuji and Golden Delicious (GD) were used to investigate cell wall metabolism and related gene expression during fruit growth and softening. Results and discussion. During fruit growth, cell wall components underwent similar changes in the two cultivars although the covalent soluble pectin (CSP) content in Fuji fruit was much higher than that in GD fruit. The activities of cell wall enzymes and the related gene expression indicated that cell wall degradation was involved in fruit growth. However, these changes showed significant differences between the two cultivars during storage. The water soluble pectin (WSP) content increased more rapidly and the content of CSP and hemi-cellulose decreased more obviously, showing a more significant correlation with firmness loss in GD fruit than with Fuji. Accordingly, the activities of cell wall enzymes and the related gene expression were significantly higher in the GD fruit. Conclusion. Cell wall metabolism and the related gene expression showed significant differences between Fuji and GD fruit during growth and softening. Both acted on fruit growth and enlargement but revealed a significant cultivar-dependency with regards to fruit softening.