Physiological, biochemical and transcriptional analysis of onion bulbs during storage

Physiological and biochemical changes occur in onion (Allium cepa L.) bulbs during the transition from dormancy to sprout suppression and subsequent sprout growth. These include changes in the concentrations of flavor compounds, carbohydrates, mineral elements and plant growth regulators (PGRs). Detailed analyses of these changes and the impact of different post-harvest techniques, designed to prolong storage life, have not been undertaken. We developed the first onion oligonucleotide microarray to determine differential gene expression in onion during curing and storage, with transcriptional changes supporting biochemical and physiological analyses. Samples of RNA were prepared from onions of two cultivars, ‘Wellington’ (brown, long-storing) and ‘Sherpa’ (brown, average-storing), grown according to normal commercial practice at various physiological ages, viz, freshly harvested, cured, pre-sprouting and sprouting. Three biological replicates for each time (harvest, cured, before sprouting, sprouting), curing temperature (20, 28°C) and cultivar (Wellington, Sherpa) combination (n = 42).