Investigations of changes in the arabinogalactan proteins (AGPs) structure, size and composition during the fruit...

Arabinogalactan proteins (AGPs) are ubiquitous cell wall and plasma membrane components and are characterised by extensive glycosylation and heterogeneity of their carbohydrate and protein units. The aim of the study was to evaluate the structural features of AGPs present in apple fruits at different stages of the ripening process. AGPs were extracted using the Yariv reagent and examined using SDS-PAGE, immunoblotting, FT-IR, and AFM. In situ analysis, immunofluorescence (CLSM) and immunogold-labelling (TEM), were performed. We demonstrated that AGPs were indeed present in apple fruits at the different stages of the ripening process. The changes in the amount (1.52-2.08 mg g^-1), diameter (152.73-75.05 nm), molecular mass (50-250 kDa), and distribution in the cell of AGPs demonstrate their variable presence and changeable structure during the ripening process. We propose specific wavenumbers, i.e. 1265 cm^-1, 1117 cm^-1, and 960 cm^-1, which could be assigned to AGPs. The immunofluorescence and immunogold-labelling results indicate that the JIM13 antibody is the most characteristic for AGPs in apple fruits. This study quantitatively demonstrated for the first time that AGP accumulation occurs in ripe fruits, which is supported by the highest AGPs content, the highest molecular mass, and the appearance of a specific distribution pattern at the cellular level.