title: Lower cell wall pectin solubilisation and galactose loss during early fruit development in apple (Malus x domestica) cultivar 'Scifresh' are associated with slower softening rate.
abstract: Substantial differences in softening behaviour can exist between fruit even within the same species. Apple cultivars 'Royal Gala' and 'Scifresh' soften at different rates despite having a similar genetic background and producing similar amounts of ethylene during ripening. An examination of cell wall metabolism from the fruitlet to the ripe stages showed that in both cultivars pectin solubilisation increased during cell expansion, declined at the mature stage and then increased again during ripening. This process was much less pronounced in the slower softening 'Scifresh' than in 'Royal Gala' at every developmental stage examined, consistent with less cell separation and softening in this cultivar. Both cultivars also exhibited a progressive loss of pectic galactan and arabinan side chains during development. The cell wall content of arabinose residues was similar in both cultivars, but the galactose residue content in 'Scifresh' remained higher than that of 'Royal Gala' at every developmental stage. The higher content of cell wall galactose residue in 'Scifresh' cell walls correlated with a lower β-galactosidase activity and more intense immunolabelling of RG-I galactan side chains in both microscopy sections and glycan microarrays. A high cell wall galactan content has been associated with reduced cell wall porosity, which may restrict access of cell wall-modifying enzymes and thus maintain better structural integrity later in development. The data suggest that the composition and structure of the cell wall at very early development stages may influence subsequent cell wall loosening, and may even predispose the wall's ensuing properties.
authors.affiliation: Food Science, School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand; The New Zealand Institute for Plant & Food Research Limited, Mount Albert Research Centre, Private Bag 92169, Auckland 1142, New Zealand. Electronic address: jovyn.ng@plantandfood.co.nz.
authors.forename: Jovyn K T
authors.initials: JK
authors.lastname: Ng
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Mount Albert Research Centre, Private Bag 92169, Auckland 1142, New Zealand. Electronic address: rosie.schroeder@plantandfood.co.nz.
authors.forename: Roswitha
authors.initials: R
authors.lastname: Schröder
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Private Bag 11600, Palmerston North 4442, New Zealand. Electronic address: david.brummell@plantandfood.co.nz.
authors.forename: David A
authors.initials: DA
authors.lastname: Brummell
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Mount Albert Research Centre, Private Bag 92169, Auckland 1142, New Zealand. Electronic address: paul.sutherland@plantandfood.co.nz.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Sutherland
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Mount Albert Research Centre, Private Bag 92169, Auckland 1142, New Zealand. Electronic address: ian.hallett@plantandfood.co.nz.
authors.forename: Ian C
authors.initials: IC
authors.lastname: Hallett
authors.affiliation: Food Science, School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand. Electronic address: bsmith.auckland@gmail.com.
authors.forename: Bronwen G
authors.initials: BG
authors.lastname: Smith
authors.affiliation: Food Science, School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand. Electronic address: l.melton@auckland.ac.nz.
authors.forename: Laurence D
authors.initials: LD
authors.lastname: Melton
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 1401, Havelock North 4157, New Zealand. Electronic address: jason.johnston@plantandfood.co.nz.
authors.forename: Jason W
authors.initials: JW
authors.lastname: Johnston
mesh_terms: D002473:Cell Wall / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005638:Fruit / Q000254:growth & development* / Q000378:metabolism*; D005685:Galactans / Q000378:metabolism; D005690:Galactose / Q000378:metabolism*; D054794:Glycomics; D027845:Malus / Q000254:growth & development* / Q000378:metabolism*; D008970:Molecular Weight; D010368:Pectins / Q000378:metabolism*; D010936:Plant Extracts / Q000737:chemistry; D012995:Solubility
chemical_list: D005685:Galactans; D010936:Plant Extracts; D010368:Pectins; D005690:Galactose
keywords: Arabinan; Cell wall; Fruit development; Fruit softening; Galactan