Oligosaccharides were isolated directly from tomato fruit tissue; a series of homo-oligogalacturonides with a DP of 2-6 was identified in red-ripe and over-ripe fruit. Two glucose disaccharides, identified as gentiobiose and nigerose, were isolated from both mature green (MG) and red-ripe fruit. Gentiobiose was able to accelerate the initiation of ripening when vacuum infiltrated into MG tomato fruit, particularly when co-infiltrated with nigerose. The possible origin of these disaccharides is discussed. The potential role of organic acids (ascorbate, citrate and oxalate) in fruit softening was evaluated <i>in vitro</i> on MG tomato fruit alcohol-insoluble residue (AIR). The hydroxyl radical (<sup>•</sup>OH), produced via a Fenton reaction in which ascorbate acts as a pro-oxidant, released pectin into solution in the presence of oxygen. <sup>•</sup>OH production <i>in vivo</i> may be localised in the PCW by the positioning of metal ions such as Cu<sup>2+</sup> on pectins or glycoproteins. Probes used to detect <sup>·</sup>OH in the tomato fruit apoplast produced inconclusive results but suggested that this active oxygen species is present during ripening. The incubation of tomato fruit AIR with naturally occurring chelators such as citrate and oxalate also led to solubilisation of uronate-containing material. The alteration of the PCW during ripening is likely to be the result of a number of processes. These processes may occur throughout the PCW or may occur in specific areas but their contribution to the softening process should not be over-looked in favour of processes only involving hydrolytic enzymes, as this could lead to an over-simplified view fruit ripening.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649767 |
| Date | January 2001 |
| Creators | Dumville, Joanne |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14767 |
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