Regulation of Cell Wall Remodeling is an Important Factor in the Reduction of Tomato Fruit Size Immediately after Fruit Set Induced by Salinity Conditions

Tomato fruits under salt stress exhibit growth inhibition, resulting in increased fruit firmness and decreased fruit size. In angiosperms, the ovary becomes a fruit upon pollination and the fruit develops through fruit formation and maturation. Since fruit size does not change after a green fruit reaches its maximum size, it is important to analyze the early stages of fruit development. Therefore, in this study, we focused on the control and properties of cell walls during the initial fruit formation process that determines tomato (Solanum lycopersicum cv. ‘Micro-Tom’) fruit size. As a result of analyzing mechanical properties, an increase in fruit hardness under salt stress conditions (160 mM NaCl) was observed in early tomato fruits during the initial fruit formation process. Furthermore, by observing changes in the distribution of cell wall polysaccharides, we found that during early fruit development including 5 DPA, which is a time of tissue expansion, the pericarp hardens due to the accumulation of cellulose. Meanwhile, Xyloglucan endotransglucosylase/hydrolase (XTH) and expansin, which are cell wall loosening enzymes, do not increase. Our results showed that the increase in fruit hardness under salt stress conditions occurred in early tomato fruits during the initial fruit formation process, and the reduction in fruit size due to salt stress was due to changes in cell wall properties during the early fruit formation process.