JXB Advance Access originally published online on June 13, 2005
Journal of Experimental Botany 2005 56(418):2029-2036; doi:10.1093/jxb/eri201
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RESEARCH PAPER |
Expression of genes encoding cell wall modifying enzymes is induced by cold storage and reflects changes in pear fruit texture
1Laboratory of Plant Molecular Biology and Biotechnology, ICAT (Institute for Applied Science and Technology), Ed. ICAT, Campo Grande, 1749-016 Lisboa, Portugal
2Department of Bacteriology, INSA (National Institute of Health), Av. Padre Cruz, 1649-016 Lisboa, Portugal
3Department of Plant Physiology, Agronomic National Station, Quinta do Marquês, 2784-505 Oeiras, Portugal
* To whom correspondence should be addressed. Fax: +351 21 7500163. E-mail: fonseca.sandra{at}gmail.com
Preclimacteric ‘Rocha’ pears stored under chilling conditions, had a larger increase of ACO (1-aminocyclopropane-1-carboxylate oxidase) activity and softened faster than those treated with ethylene. Non-treated fruit did not ripen or soften, acquired a rubbery texture, and showed barely detectable levels of ACO activity. The transcript accumulation of seven genes encoding cell wall modifying enzymes was followed during fruit growth, ripening, and senescence, and in fruit that failed to ripen, by quantitative real-time PCR. Transcripts from ‘Rocha’ pear polygalacturonase1 and 2 (PcPG1, PcPG2), ß-galactosidase (PcßGAL) and ß-xylosidase (PcXYL) genes accumulated up to 1000-fold at the climacteric onset, while low transcript levels were detected in growing fruit. In fruit that did not ripen, this transcript accumulation was lower compared with fruits that ripened normally. Transcripts for expansin1 and 2 (PcEXPA1, PcEXPA2) accumulated in growing fruit, but about 10-fold more in fruit after rewarming. Xyloglucan endotransglucosylase/hydrolase (PcXTH) had the highest basal expression levels in all samples, showing only a small increase during fruit growth and ripening. PcEXPA2 and PcXTH transcripts accumulated in untreated fruit, 21 d after harvest, to levels similar to those of fruit that ripened normally. Since in untreated fruit ACO activity was barely detectable, it is likely that the activation of these genes might occur at very low ethylene levels. Results suggest that PcXTH and PcEXPA2 gene induction might be associated with cell wall maintenance during ‘Rocha’ pear development and ripening, while PcEXPA1, PcPG1, PcPG2, PcßGAL, and PcXYL expression is likely to be related to cell wall disassembly and loosening.
Key words: Cell wall, cold storage, fruit ripening, gene expression, pear, softening
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