Teacher:In this task, you are given a passage which has a question and the context. You have to generate an answer to the question based on the information present in the context.
Teacher: Now, understand the problem? Solve this instance: Context: Many fruits soften during ripening, which is important commercially and in rendering the fruit attractive to seed-dispersing animals. Cell-wall polysaccharide hydrolases may contribute to softening, but sometimes appear to be absent. An alternative hypothesis is that hydroxyl radicals (()OH) non-enzymically cleave wall polysaccharides. We evaluated this hypothesis by using a new fluorescent labelling procedure to 'fingerprint' ()OH-attacked polysaccharides.", 'We tagged fruit polysaccharides with 2-(isopropylamino)-acridone (pAMAC) groups to detect (a) any mid-chain glycosulose residues formed in vivo during ()OH action and (b) the conventional reducing termini. The pAMAC-labelled pectins were digested with Driselase, and the products resolved by high-voltage electrophoresis and high-pressure liquid chromatography.', 'Strawberry, pear, mango, banana, apple, avocado, Arbutus unedo, plum and nectarine pectins all yielded several pAMAC-labelled products. GalA-pAMAC (monomeric galacturonate, labelled with pAMAC at carbon-1) was produced in all species, usually increasing during fruit softening. The six true fruits also gave pAMACUA-GalA disaccharides (where pAMACUA is an unspecified uronate, labelled at a position other than carbon-1), with yields increasing during softening. Among false fruits, apple and strawberry gave little pAMACUA-GalA; pear produced it transiently.\Question: Are pectic polysaccharides attacked by hydroxyl radicals in ripening fruit : evidence from a fluorescent fingerprinting method?
Student:
GalA-pAMAC arises from pectic reducing termini, formed by any of three proposed chain-cleaving agents (()OH, endopolygalacturonase and pectate lyase), any of which could cause its ripening-related increase. In contrast, pAMACUA-GalA conjugates are diagnostic of mid-chain oxidation of pectins by ()OH. The evidence shows that ()OH radicals do indeed attack fruit cell wall polysaccharides non-enzymically during softening in vivo. This applies much more prominently to drupes and berries (true fruits) than to false fruits (swollen receptacles). ()OH radical attack on polysaccharides is thus predominantly a feature of ovary-wall tissue.