Cell Wall Calcium and Hemicellulose Have a Role in the Fruit Firmness during Storage of Blueberry (Vaccinium spp.)

Abstract

The firmness of blueberry is one of its most significant quality attributes. Modifications in the composition of the cell wall have been associated with changes in the fruit firmness. In this work, cell wall components and calcium concentration in two blueberry cultivars with contrasting firmness phenotypes were evaluated at harvest and 30 days cold storage (0 °C). High performance anion-exchange chromatography with pulse amperometric detector (HPAEC-PAD) analysis was performed using the “Emerald” (firmer) and “Jewel” (softer) blueberry cultivars, showing increased glucose in the firmer cultivar after cold storage. Moreover, the LM15 antibody, which recognizes xyloglucan domains, displayed an increased signal in the Emerald cultivar after 30 d cold storage. Additionally, the antibody 2F4, recognizing a homogalacturonan calcium-binding domain, showed a greater signal in the firmer Emerald blueberries, which correlates with a higher calcium concentration in the cell wall. These findings suggest that xyloglucan metabolism and a higher concentration of cell wall calcium influenced the firmness of the blueberry fruit. These results open new perspectives regarding the role of cell wall components as xyloglucans and calcium in blueberry firmness.

Pre-Anthesis Cytokinin Applications Increase Table Grape Berry Firmness by Modulating Cell Wall Polysaccharides

“…These findings correlate with the presence of the egg-box structure observed in the inner mesocarp cells at anthesis, suggesting that the presence of this dimerization could prevent HG degradation by HG-degrading enzymes, such as polygalacturonases and pectate lyases [53]. Furthermore, a previous study described a correlation between an increase in the calcium content of berries and higher firmness concomitant with the role of this cation in the HG egg-box structure [27]. The analysis of cell wall composition indicates that pre-anthesis CPPU applications have an impact in the mesocarp tissue, exhibiting an overall increased accumulation of sugar monomers in the cell wall and suggesting an increased amount of pectin and hemicellulose in CPPU-treated grape berries.…”

“…Regarding hemicellulose, epicarp and mesocarp tissues contain an increased amount of different XyG monosaccharides, suggesting that pre-anthesis CPPU applications could promote xyloglucan synthesis during grape berry development. Homogalacturonan is the pectinic domain of cell wall components most widely associated with firmness in different berry fruits [2,27,[50][51][52]. The analyses indicate that pre-anthesis CPPU applications induce an increased accumulation of GalA and cell wall-associated calcium than control samples in the mesocarp tissue.…”

“…To obtain a better understanding of the relation between changes in cell wall composition and phenotypic features, a characterization of the berry weight, berry width, total soluble solids, titratable acidity, and hardness of CPPU-treated and control grape berries was performed at harvest. Texture profile analysis (TPA) is composed of several parameters, with hardness being considered a suitable indicator of firmness in different berries [27,36]. The CPPU-treated and control grape berries exhibited similar weights, widths, and total soluble solids, but contrasting titratable acidity and hardness (firmness) (Figure 4D).…”

“…During later stages in development, the inner and outer mesocarp cells are differentiated in the flesh and epicarp fruit tissues, respectively. Recent studies in blueberries' epicarp and mesocarp tissues have described that the egg-box motif, formed by cross-linking between demethylesterified HG and calcium, and xyloglucan polymers are key molecules involved in fruit firmness and fruit size determination [27,44]. Thus, the increase in 2F4 labeling implies the presence of an egg-box structure in a group of cells, suggesting a stiffening of these cell layers that form the future mesocarp [4].…”

“…RG-I differs from these three pectin domains because its backbone is formed by a repeated α-D-(1,4)-GalA-α-L-(1,2)-Rha (rhamnose) disaccharide that can be substituted with side-chain structures containing both galactose (Gal) and arabinose (Ara) units [26]. Additionally, a recent study has described the implications of cell wall composition in berry fruit size and firmness, suggesting the relevance of cell wall polysaccharide architecture in this complex process and producing interesting commercial and agronomical traits [27].…”