Abstract
Fruit ripening is one of the developmental processes accompanying seed development. The tomato is a well-known model for studying fruit ripening and development, and the disassembly of primary cell walls and the middle lamella, such as through pectin de-methylesterified by pectin methylesterase (PE) and depolymerization by polygalacturonase (PG), is generally accepted to be one of the major changes that occur during ripening. Although many reports of the changes in pectin during tomato fruit ripening are focused on the relation to softening of the pericarp or the Blossom-end rot by calcium (Ca2+) deficiency disorder, the changes in pectin structure and localization in each tissues during tomato fruit ripening is not well known. In this study, to elucidate the tissue-specific role of pectin during fruit development and ripening, we examined gene expression, the enzymatic activities involved in pectin synthesis and depolymerisation in fruit using biochemical and immunohistochemical analyses, and uronic acids and calcium (Ca)-bound pectin were determined by secondary ion-microprobe mass spectrometry. These results show that changes in pectin properties during fruit development and ripening have tissue-specific patterns. In particular, differential control of pectin methyl-esterification occurs in each tissue. Variations in the cell walls of the pericarp are quite different from that of locular tissues. The Ca-binding pectin and hairy pectin in skin cell layers are important for intercellular and tissue–tissue adhesion. Maintenance of the globular form and softening of tomato fruit may be regulated by the arrangement of pectin structures in each tissue.
Highlights
Fruit ripening is a developmental process accompanying seed development
Small effects on fruit softening can be achieved by individual gene knockdowns [9,14], substantial changes in fruit texture are likely to require the simultaneous modulation of multiple pectin degradation-related genes
To elucidate the tissue-specific role of pectin during fruit development and ripening, we examined the expression of pectin biosynthesis/depolymerization genes, targeting glycosyltransferase-1-like gene (GAUT1-like), pectin esterase (PE2) and polygaracturonase 2 (PG2)
Summary
Fruit ripening is a developmental process accompanying seed development. In fleshy fruits, this involves many physiological processes, including the production of nutrients and aromatic compounds, changes in colour and softening of the pericarp, which evolved to attract animals and promote seed dispersal [1]. A decrease in fruit firmness occurs due to dissolution of the primary cell wall and middle lamella, resulting in a reduction in intercellular adhesion, depolymerization and solubilisation of hemicellulosic and pectic cell wall polysaccharides [9] These events are accompanied by increased expression of various cell wall-degradation enzymes. Pectin depolymerization is well known to be a characteristic change in tomato fruit ripening, it does not directly affect fruit softening and firmness. Recently, it was suggested pectin de-methlesterification by PE effects to BER in tomato fruit. We tried immunohistochemical analyses of uronic acids and calcium (Ca)-bound pectin localization in whole tomato fruit
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