). At the cell-wall level, fruit softening is a result of changes in interactions among cell-wall polysaccharides and their breakdown ( Knee, 1975 ). These changes in cell walls result from the activities of cell-wall–modifying enzymes. Ripening
storage quality of mango fruit, suggesting that ethylene biosynthesis may be associated with the occurrence of CI ( Nair and Singh, 2003 ). CI also causes damage to the cell wall of mango fruit, which includes the loss of wall structural integrity ( Han et
The irradiation of harvested fruit is typically accompanied by excessive tissue softening, a process that is not well understood. In this study, we examined the role of specific cell wall polymers and the extent of general cell wall degradation and softening in irradiated tomato fruit. `Sunny' tomato fruit at mature-green and pink stages were subjected to X-ray radiation at 0, 83, and 156 Krad. Immediate softening was noted for both maturation classes, although some postirradiation recovery was evident in green fruit. Pectic polymers of both mature-green and pink fruit exhibited depolymerization and altered neutral sugar profiles in response to irradiation. Pectins, either as components of total ethanol-insoluble solids (EIS), purified by selective extraction, or of commercial origin were similarly affected by irradiation. Cellulose preparations were unaffected by irradiation. The data demonstrate that the effect of irradiation on the cell wall exhibits specificity, can occur nonenzymatically, and does not require initiating adducts of cytosolic origin.
radial walls of the phellogen, determined by their lability and proneness to fracture, that determines the resistance to skinning ( Lulai, 2002 ). There is no information on how cell wall enzyme activity varies in sweetpotato. Pectinases are
Cell wall changes during ripening have a major effect on fruit texture. The cell walls isolated using phenol-Tris buffer were sequentially extracted to give polysaccharide fractions that contained mainly water-soluble pectin, chelator-soluble (CDTA) pectin, hemicelluloses (0.05 M Na2CO3 followed by 1M and 4M KOH) and cellulose. The fractions were analyzed colorimetrically for uronic acid, total neutral sugar and cellulose contents. The component sugars of each fraction were determined as their alditol acetates by GC. Then was a decrease in the two pectin fractions during ripening. The pectins appear to have arabinan and galactan side chains. Pectic galactose decreases during ripening. The weight of the combined hemicellulose fractions did not change during ripening, nor did the cellulose level. At least two types of arabinan are present. Pectins were found in all cell wall fractions. Nashi cell walls contain a relatively large amount of xylan compared to other fruit.
Cell wall synthesis during development and ripening of `Rutgers', rin and nor tomato (Lycopersicon esculentum Mill.) fruit was quantified by monitoring incorporation of 14C into outer pericarp cell walls after pedicel injection of (U-14C) - sucrose. Fruit color (Hunter “a” and “b” values) and firmness (Instron) were also monitored. 14C-Incorporation continued throughout development and ripening in `Rutgers' cell walls and exhibited a transient increase from late maturegreen to the turning stage. Incorporation of 14C into cell walls of rin pericarp tissue was similar to `Rutgers' at 20 days pest-anthesls (DPA) (immature-green) but decreased to a level similar to red `Rutgers' fruit by 35 DPA. Incorporation of 14C into nor pericarp cell walls was low throughout the experimental period (20 to 75 DPA). In contrast to previous reports, rin and nor pericarp tissue exhibitad a decrease in firmness of the outer pericarp. However, the rate of softening was slower than in `Rutgers'. Pericarp tissue from rin and nor fruit at 70 and 75 DPA, respectively, resisted compression as much as pink `Rutgers' pericarp tissue.
Fruit extracts of Lycopersicon esculentum cv. Tiny Tim were found to contains α- and β-galactosidase, a- and β-glucosidase, α- and β-mannosidase, and α- and β-xylosidase activities. All of these enzymes either declined or remained constant in concentration during fruit development and ripening. Activities of β-glucosidase and α-galactosidase were found to be associated with isolated cell wall fragments. No evidence was found for an increase in concentration of the enzymes in the cell wall during ripening. The probability that these enzymes are not involved in fruit softening is discussed.
al., 2005 ; Newhouse et al., 2007 ), and small-scale field tests of transgenic elms have been established ( Merkle et al., 2007 ). Determination of the chemical attributes of plant cell walls is of great importance for evaluating both the effects of
Nectarine fruit (Prunus persica (L) Batsch) cv. Fantasia, were ripened immediately after harvest (normal ripening), or stored for 6 weeks either continuously at 0°C or were intermittently warmed (IW) for 48 h at 20C after 2 and 4 weeks, and then ripened. Fruit subjected to IW ripened normally, whereas the continuously stored fruit developed mealiness during ripening. Normal ripening was associated with solubilization and depolymerization of pectic polymers and a net loss of galactose. Only limited pectic solubilization and removal of side chains occurred during ripening of mealy fruit. Pectic polymer polymerization occurred at each IW occasion continued during ripening after storage, but was not as extensive as in normally ripened fruit. Mealy fruit had high autolytic capacity, probably as a result of insoluble pectic polymers in the cell wall that were not solubilized during ripening. The release of uronic acid suggests that cool storage temperatures do not irreversibly inhibit polygalacturonase activity.
Softening and liquefaction of `Solar Set' locules was studied by examining cell wall polysaccharides during fruit developmental stages (FDS) of immature green, mature green and breaker. Ethanol insoluble solids (EIS) were sequentially extracted by H2O, CDTA, and Na2CO3 solutions. The chromatograms of gel filtration among the same-solution extracts of EISs from three FDS were similar. Gradient DEAE also yielded similar patterns among FDS in each extraction solvent, even though the patterns of Na2CO3 extracts differed from those of H2O and CDTA extracts. The mole ratio of total polyuronides decreased for Gal, Ara, and Xyl at later FDS in both EIS and in all extracted polymers. Gal had the highest mole percentage of total neutral sugars, followed by Ara, Xyl, and Rha. While the mole percentage of neutral sugars for Gal, Rha, Ara, and Xyl were relatively similar among FDS in H2O extracts, those in CDTA and Na2CO3 extracts either increased or decreased, depending on individual neutral sugar. SDS-PAGE showed increased density in locule-tissue proteins, especially one with a molecular weight of less than 20 kDa, during later FDS. Results indicate that pectin depolymerization was limited and major neutral sugars commonly composing side chains showed a net decrease.