In vivo and in vitro swelling of cell walls during fruit ripening

Abstract

Swelling properties of the cell walls of nine temperate fruit species, selected for their dierent ripening and textural characteristics, were studied during ripening. Cell wall swelling was examined in intact fruit using microscopy techniques and in vitro, using cell wall material isolated from fruit tissue. In fruit which ripened to a soft melting texture (persimmon, avocado, blackberry, strawberry, plum), wall swelling was pronounced, particularly in vitro. In-vivo swelling was marked only in avocado and blackberry. Fruit which ripened to a crisp, fracturable texture [apple (two cultivars), nashi pear, watermelon] did not show either in-vivo or in-vitro swelling of the cell wall. There was a correlation between swelling and the degree of pectin solubilisation, suggesting that wall swelling occurred as a result of changes to the viscoelastic properties of the cell wall during pectin solubilisation. Chemical and enzymatic removal of pectin from kiwifruit cell wall material supported the idea that swelling is associated with movement of water into voids left in the cellulose-hemicellulose network by the solubilised pectin. However, the results also suggested that swelling in vivo was more complex than this, and that the physicochemical changes which led to swelling included other elements of cell wall modi®cation involving the site and mechanism of pectin solubilisation andor the cellulose-xyloglucan complex.

Manipulation of Strawberry Fruit Softening by Antisense Expression of a Pectate Lyase Gene

“…In two of them, it has been confirmed that the amount of pectate lyase protein was parallel to the transcript level. Cell wall swelling during softening is common in many fruits, including strawberry (Redgwell et al, 1997). This fact can be related to an increase of pore size due to disassembly of pectin networks induced by pectin-degrading enzymes (Redgwell, 1997;Hadfield and Bennett, 1998).…”

“…Cell wall swelling during softening is common in many fruits, including strawberry (Redgwell et al, 1997). This fact can be related to an increase of pore size due to disassembly of pectin networks induced by pectin-degrading enzymes (Redgwell, 1997;Hadfield and Bennett, 1998). As expected, inhibition of pectate lyase gene resulted in a lower degree of in vitro cell wall swelling and a lower amount of ionically bound pectins, the pectin fraction solubilized by pectin-degrading enzymes such as pectate lyase, indicating a higher integrity of cell wall structure in transgenic ripen fruit.…”

“…Histological analysis of ripe fruit showed a cell wall thinner than unripe fruit and the lost of intercellular material, the cells being with little contact and separated by considerable intercellular space (Redgwell et al, 1997). The underlying biochemical mechanism of strawberry softening is unclear.…”

“…The largest changes in the plant cell wall during ripening occur in the pectin component. The percentage of water-soluble pectins increases during ripening but total quantity of polyuronide residues (Woodward, 1972; Knee et al, 1977; Huber, 1984;Redgwell et al, 1997) and polyuronide length (Huber, 1984;Redgwell et al, 1997) are only slightly modified. This last observation is in accordance with the low poligalacturonase activity found in ripe fruit (Abeles and Takeda, 1990;Nogata et al, 1993).…”

“…The residue was filtered by glass microfiber filters (Whatman, Maidstone, UK), washed with acetone, and dried in vacuum. In vitro cell wall swelling was estimated as previously described (Redgwell et al, 1997). Chelator-soluble pectins were extracted by incubation of 3 to 5 mg of CWM in 2 mL of 50 mm CDTA for 4 h, and measured with the m-hydroxydiphenyl reagent (Blumenkrantz and AsboeHansen, 1973).…”