Arabinogalactan protein is a molecular and cytological marker of particular stages of the tomato fruit ripening process

Abstract

Arabinogalactan proteins (AGPs) are constituents of the plant cell walls, which are increasingly being considered as essential molecules in the formation of the extracellular matrix. Given their molecular structure and the advantage of the carbohydrate moiety, the glycosylation level and its modification is assumed as a cause of the functional diversity of AGPs. The aim of current work was to evaluate the molecular features of AGP as a potential molecule involved in the ripening process. For this purpose, tomato fruits were analyzed at specific five stages of ripening using microscopic and molecular tools. The experiment showed that the high content and the occurrence of the AGP molecule with molecular weight around 120 kDa are related to cell wall conditions and the intensity of ongoing glycosylation. At the breaker and/or turning stage, the processes of modification of the sugar moiety and depolymerization begin to prevail. At the red ripe/pink stage, the synthesis process is replaced by the degradation process, which is associated with the disappearance of AGPs with high molecular weights and the appearance of only single sugar residues with very low molecular weights. The occurrence of AGPs with low molecular weight (∼30 kDa) may be used as a marker of the finalization of the ripening process in tomato fruits. All anatomical and morphological alterations in the cell wall confirm the presence of dependencies and connections between components of the cell wall network. We may presume that selected antibodies (JIM13, LM2, LM14) indicate very specific features of the fruit tissue at different stages of ripening; thus, AGP is a molecular and cytological marker of particular stages of the fruit ripening process.