Cell Turgor Changes Associated with Ripening in Tomato Pericarp Tissue

Abstract

The pressure microprobe was used to determine whether the turgor pressure in tomato (Lycopersicon esculentum Mill., variety "Castelmart") pericarp cells changed during fruit ripening. The turgor pressure of cells located 200 to 500 micrometers below the fruit epidermis was uniform within the same tissue (typically ± 0.02 megapascals), and the highest turgors observed (<0.2 megapascals) were much less than expected, based on tissue osmotic potential (-0.6 to -0.7 megapascals). These low turgor values may indicate the presence of apoplastic solutes. In both intact fruit and cultured discs of pericarp tissue, a small increase in turgor preceded the onset of ripening, and a decrease in turgor occurred during ripening. Differences in the turgor of individual intact fruit occurred 2 to 4 days before parallel differences in their ripening behavior were apparent, indicating that changes in turgor may reflect physiological changes at the cell level that precede expression of ripening at the tissue level.

A Reevaluation of the Key Factors That Influence Tomato Fruit Softening and Integrity

“…6A). The turgor values are comparable to those previously reported for other tomato cultivars (Shackel et al, 1991). The initial cellular turgor pressure and rate of linear decrease were similar in DFD fruits at the MG stage and the onset of ripening.…”

“…It has been suggested that fruit firmness, in common with the biomechanical properties of most plant tissues, is influenced by cellular turgor pressure (Shackel et al, 1991;Jackman et al, 1992;Jackman and Stanley, 1995;Mignani et al, 1995;Harker et al, 1997;Barrett et al, 1998). This idea has yet to be proven experimentally, but is supported by our data and other studies that have shown that ectopic application of wax to avocado (Persea americana) fruits can prolong their firmness (Jeong et al, 2003).…”

“…These events are accompanied by the increased expression of numerous cell wall degrading enzymes, including polysaccharide hydrolases, transglycosylases, lyases, and other wall loosening proteins, such as expansin (Harker et al, 1997;Rose et al, 2003;Brummell, 2006). Accordingly, while factors such as cellular turgor and morphology (Lin and Pitt, 1986;Shackel et al, 1991) have been suggested to contribute to aspects of texture, mechanistic models almost invariably attribute fruit softening to disassembly of polysaccharide networks in the primary wall and middle lamella (Rose et al, 2003;Brummell, 2006). For example, polygalacturonase (PG)-catalyzed depolymerization of pectin in the wall and middle lamella was long believed to be the principal process underlying fruit softening, although this was refuted through reverse genetics studies in tomato (for review, see Brummell and Harpster, 2001).…”

Elastic stresses and plastic deformations in 'Santa Clara' tomato fruits caused by package dependent compression

“…2). The flattening pressure obtained for each ripening index of 'Santa Clara' tomato fruit had a magnitude similar to the turgor observed in a pressure probe study of Shackel et al (1991) in ripening tomatoes. One possible explanation of the reduction of turgor in tomatoes during ripening is the reduction for the solute pumping from the apoplast to the simplast, which causes an increase in the concentration of solutes in the apoplast as observed by Shackel et al (1991).…”

“…5A). The existence of gluing components in the external surface of the cell walls facing intercellular volumes (Steckel et al, 1995) and the turgor reduction during ripening (Shackel et al, 1991) (Fig. 2) are the possible interdependent causes for the much smaller elastic gas volume recovery in red fruits.…”