Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit

evidence from a fluorescent fingerprinting method

Babul Airianah Othman, Robert A M Vreeburg, Stephen C. Fry

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

BACKGROUND AND AIMS: 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.

METHODS: 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.

KEY RESULTS: 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 pAMAC·UA-GalA disaccharides (where pAMAC·UA 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 pAMAC·UA-GalA; pear produced it transiently.

CONCLUSIONS: 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, pAMAC·UA-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.

Original languageEnglish
Pages (from-to)441-455
Number of pages15
JournalAnnals of Botany
Volume117
Issue number3
DOIs
Publication statusPublished - 1 Mar 2016

Fingerprint

hydroxyl radicals
ripening
polysaccharides
fruits
pectins
methodology
pears
strawberries
carbon
apples
cell walls
fluorescent labeling
Arbutus unedo
pectate lyase
nectarines
stone fruits
disaccharides
avocados
rendering
plums

Keywords

  • cell wall
  • fingerprint compounds
  • fluorescent labelling
  • Fruit
  • hydroxyl radicals
  • non-enzymic scission
  • pectic polysaccharides
  • ripening

ASJC Scopus subject areas

  • Plant Science

Cite this

Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit : evidence from a fluorescent fingerprinting method. / Othman, Babul Airianah; Vreeburg, Robert A M; Fry, Stephen C.

In: Annals of Botany, Vol. 117, No. 3, 01.03.2016, p. 441-455.

Research output: Contribution to journalArticle

@article{a634efe5522b4675bcb0fdbd1e9b3f85,
title = "Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit: evidence from a fluorescent fingerprinting method",
abstract = "BACKGROUND AND AIMS: 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.METHODS: 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.KEY RESULTS: 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 pAMAC·UA-GalA disaccharides (where pAMAC·UA 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 pAMAC·UA-GalA; pear produced it transiently.CONCLUSIONS: 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, pAMAC·UA-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.",
keywords = "cell wall, fingerprint compounds, fluorescent labelling, Fruit, hydroxyl radicals, non-enzymic scission, pectic polysaccharides, ripening",
author = "Othman, {Babul Airianah} and Vreeburg, {Robert A M} and Fry, {Stephen C.}",
year = "2016",
month = "3",
day = "1",
doi = "10.1093/aob/mcv192",
language = "English",
volume = "117",
pages = "441--455",
journal = "Annals of Botany",
issn = "0305-7364",
publisher = "Oxford University Press",
number = "3",

}

TY - JOUR

T1 - Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit

T2 - evidence from a fluorescent fingerprinting method

AU - Othman, Babul Airianah

AU - Vreeburg, Robert A M

AU - Fry, Stephen C.

PY - 2016/3/1

Y1 - 2016/3/1

N2 - BACKGROUND AND AIMS: 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.METHODS: 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.KEY RESULTS: 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 pAMAC·UA-GalA disaccharides (where pAMAC·UA 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 pAMAC·UA-GalA; pear produced it transiently.CONCLUSIONS: 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, pAMAC·UA-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.

AB - BACKGROUND AND AIMS: 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.METHODS: 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.KEY RESULTS: 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 pAMAC·UA-GalA disaccharides (where pAMAC·UA 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 pAMAC·UA-GalA; pear produced it transiently.CONCLUSIONS: 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, pAMAC·UA-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.

KW - cell wall

KW - fingerprint compounds

KW - fluorescent labelling

KW - Fruit

KW - hydroxyl radicals

KW - non-enzymic scission

KW - pectic polysaccharides

KW - ripening

UR - http://www.scopus.com/inward/record.url?scp=85016039258&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85016039258&partnerID=8YFLogxK

U2 - 10.1093/aob/mcv192

DO - 10.1093/aob/mcv192

M3 - Article

VL - 117

SP - 441

EP - 455

JO - Annals of Botany

JF - Annals of Botany

SN - 0305-7364

IS - 3

ER -