dc.contributor.advisor |
Marsh, K |
en |
dc.contributor.advisor |
Nicolau, L |
en |
dc.contributor.author |
Guenther, Catrin |
en |
dc.date.accessioned |
2011-06-20T21:25:31Z |
en |
dc.date.issued |
2010 |
en |
dc.identifier.uri |
http://hdl.handle.net/2292/6833 |
en |
dc.description.abstract |
Innovation in kiwifruit flavour is desired. This can be achieved by affecting secondary metabolites. Here the biosynthesis of flavour-related methylsulfanyl (MeS)- volatiles in Actinidia chinensis, their genetic background and regulation by ethylene were investigated. Initially, headspace solid-phase microextraction (HS-SPME) and dynamic headspace sampling (DHS) parameters were systematically optimised to ensure highest extraction yields of MeS-volatiles from kiwifruit tissue using GC-MS. However, the qualitative and quantitative MeS-volatile profiles were improved using DHS compared with HS-SPME, making this the more sensitive and preferred method. MeS-volatile levels were then quantified during ripening and storage (1.5⁰C) of A. chinensis 'Hort16A'. The majority of MeS-compounds were specific for eating-ripe fruit and their concentrations increased in parallel with the climacteric rise in ethylene. No ethylene production was observed after long-term storage (4-6 months) and the levels of all MeS-volatiles, except methional, declined by 98-100% during that period. Transcript accumulation (RT-PCR) of six putative alcohol acyltransferase (AAT) was ripeningspecific and these levels decreased after prolonged cold storage concomitantly with (MeS)alkanoate ester production of fruit and cell-free extracts. However, ester production and gene expression was recovered by ethylene treatment after five months at 1.5⁰C, indicating that the biosynthesis of (MeS)alkanoate esters was likely to be ethyleneregulated in 'Hort16A'. The limiting steps of ethylene-dependent (MeS)alkanoate ester biosynthesis were then further investigated using closely related A. chinensis genotypes. Quantification of MeScompounds revealed little variation in their volatile composition but remarkable differences in the magnitude of their fruit volatile levels. Enzyme kinetic studies using cell-free extracts were performed to test whether this was caused by the catalytic properties of genotypespecific AATs. The substrate preferences were similar for most genotypes, thus suggesting substrate availability as the limiting factor for (MeS)alkanoate ester biosynthesis in A. chinensis. A link between precursor formation and ethylene biosynthesis in kiwifruit is proposed. Finally, ripening-specific AATs from Actinidia were characterised after recombinant expression. Striking differences in substrate preferences were found for two phylogenetically distinct AATs either exhibiting benzoyl-CoA: alcohol O-acyltransferase or acetyl-CoA: alcohol O-acyltransferase activity. An increased preference for benzoyl-CoA was associated with increased specificity for (MeS)alkanoyl-CoAs, thus suggesting a role of three likely orthologues in their production. |
en |
dc.publisher |
ResearchSpace@Auckland |
en |
dc.relation.ispartof |
PhD Thesis - University of Auckland |
en |
dc.relation.isreferencedby |
UoA99215803314002091 |
en |
dc.rights |
Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. |
en |
dc.rights.uri |
https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm |
en |
dc.title |
Investigation of flavour-related sulphur metabolism in Actinidia chinensis genotypes |
en |
dc.type |
Thesis |
en |
thesis.degree.discipline |
Chemistry |
en |
thesis.degree.grantor |
The University of Auckland |
en |
thesis.degree.level |
Doctoral |
en |
thesis.degree.name |
PhD |
en |
dc.rights.holder |
Copyright: The author |
en |
pubs.peer-review |
false |
en |
pubs.elements-id |
211930 |
en |
pubs.record-created-at-source-date |
2011-06-21 |
en |
dc.identifier.wikidata |
Q112883400 |
|