Journal Article

Physiological, biochemical and transcriptional analysis of onion bulbs during storage

Gemma A. Chope, Katherine Cools, John P. Hammond, Andrew J. Thompson and Leon A. Terry

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 109, issue 4, pages 819-831
Published in print March 2012 | ISSN: 0305-7364
Published online January 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcr318
Physiological, biochemical and transcriptional analysis of onion bulbs during storage

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

During the transition from endo-dormancy to eco-dormancy and subsequent growth, the onion bulb undergoes the transition from sink organ to source, to sustain cell division in the meristematic tissue. The mechanisms controlling these processes are not fully understood. Here, a detailed analysis of whole onion bulb physiological, biochemical and transcriptional changes in response to sprouting is reported, enabling a better knowledge of the mechanisms regulating post-harvest onion sprout development.

Methods

Biochemical and physiological analyses were conducted on different cultivars (‘Wellington’, ‘Sherpa’ and ‘Red Baron’) grown at different sites over 3 years, cured at different temperatures (20, 24 and 28 °C) and stored under different regimes (1, 3, 6 and 6 → 1 °C). In addition, the first onion oligonucleotide microarray was developed to determine differential gene expression in onion during curing and storage, so that transcriptional changes could support biochemical and physiological analyses.

Key Results

There were greater transcriptional differences between samples at harvest and before sprouting than between the samples taken before and after sprouting, with some significant changes occurring during the relatively short curing period. These changes are likely to represent the transition from endo-dormancy to sprout suppression, and suggest that endo-dormancy is a relatively short period ending just after curing. Principal component analysis of biochemical and physiological data identified the ratio of monosaccharides (fructose and glucose) to disaccharide (sucrose), along with the concentration of zeatin riboside, as important factors in discriminating between sprouting and pre-sprouting bulbs.

Conclusions

These detailed analyses provide novel insights into key regulatory triggers for sprout dormancy release in onion bulbs and provide the potential for the development of biochemical or transcriptional markers for sprout initiation. Evidence presented herein also suggests there is no detrimental effect on bulb storage life and quality caused by curing at 20 °C, producing a considerable saving in energy and costs.

Keywords: Allium cepa; onion; dormancy; eco-dormancy; endo-dormancy; microarray; non-structural carbohydrates; phytohormones; sprout suppression; post-harvest storage

Journal Article.  10372 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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