Cell wall metabolism during the growth of peach fruit: Association of hardness with cell wall pectins

•The hardness of peach fruit firstly increased and then decreased during growth.•Increased hardness resulted from thickening cell wall and high density middle lamella.•The molecular composition of WPP, CPP, and APP were explored during growth.•The Mw, GalA content and DE of CPP were closely related to fruit hardness. In this study, molecular composition of cell wall polysaccharides of peach during growth was investigated to elucidate influencing mechanism of hardness which regulated fruit quality. Results revealed that as fruit grew stage I to V (almost 36 to 103 day after flowering), hardness firstly increased and then decreased, reaching its peak in stage II. Microstructure indicated an increase in cell wall thickness and a transition from compact to loose adhesion between cell walls from stage Ⅰ to Ⅱ. Moreover, molecular weight (Mw), monosaccharide composition and fourier transform infrared spectra (FTIR) of peach polysaccharides extracted by water (WPP), chelating agent (CPP) and alkali (APP) indicated Mw of WPP and APP showed a downward trend and reaching the highest in stage II for CPP. Similar tendency appeared in the galacturonic acid (GalA) content. Content of galactose and arabinose in all polysaccharide decreased. Degree of esterificationa (DE) of CPP was the lowest in stage II. An increasing trend appeared in WPP. Finally, β-Galactosidase, α-l-arabinofuranosidase, pectin methyl esterase, polygalacturonase and their associated genes were analyzed to be evidence of the change of molecular composition. Above results implied Mw, GalA content and DE of CPP related with hardness during growth.