Ethylene Promotes Fruit Softening of ‘Nanguo’ Pear via Cell Wall Degradation

Fruit ripening is a complex physiological and metabolic process regulated by plant hormones. The ripening of climacteric fruits is accompanied by softening, especially ‘Nanguo’ pear. The importance of ethylene in fruit softening is well established; however, an understanding of its effects during the later stages of fruit development requires further investigation. In this study, ethylene was sprayed on ‘Nanguo’ pear fruits before harvest resulting in enhanced fruit quality by increasing the soluble solid and sugar contents while decreasing the stone cell content. Additionally, ethylene promoted the activities of polygalacturonase, pectin methylesterase, cellulase, and β-galactosidase enzymes that play a critical role in cell wall metabolism, by up-regulating PuPG and PuPG2 expression. This leaded to changes in the cell wall structure and breakdown of its components, a reduction of cellulose and original pectin content, and an increase in water-soluble pectin content. These results indicate that ethylene enhances fruit softening by up-regulating the expression of genes involved in cell wall metabolism to facilitate the activity of cell wall degrading enzymes.