Expression of genes encoding cell wall modifying enzymes is induced by cold storage and reflects changes in pear fruit texture

Abstract

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), beta-galactosidase (PcbetaGAL) and beta-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, PcbetaGAL, and PcXYL expression is likely to be related to cell wall disassembly and loosening.

Respiration rate and ethylene metabolism of ‘Jonagold’ apple and ‘Conference’ pear under regular air and controlled atmosphere

“…in 'Barttlet' pear with yellowing, softening and induction of internal disorders and superficial scald (Bower et al 2003) as also in 'Conference' (De Wild et al 1999) and 'Rocha' pears (Fonseca et al 2005). Normally apples are more sensitive to ethylene than pears.…”

“…Fruit are harvested at a mature pre-climacteric stage and stored for several months at low temperature. Mainly in pear, cooling induces, after rewarming, a uniform ripening process with the development of satisfactory aroma and fruit texture via ethylene biosynthesis (Fonseca et al 2005).…”

Indução do amadurecimento de peras 'Rocha' submetidas à baixa temperatura e à aplicação de etileno

“…A aplicação de 100 ppm de C 2 H 4 por 1 ou 2 dias não produziu efeito sobre a taxa de produção de etileno e proporcionou taxa de produção similar à do tratamento controle durante todo o período de avaliação. Fonseca et al (2005) observaram que a atividade da ACC oxidase de peras aumentou com a exposição a 100 ppm de C 2 H 4 , mas que esse aumento foi menos pronunciado em relação a frutos que foram submetidos ao frio por 60 dias a 0ºC.…”

“…Para peras 'Packham's Triumph', colhidas com firmeza de polpa de 72 N, o tempo mínimo é de 20 dias, em condições de frio a -1ºC, para induzir o amadurecimento (Seibert et al, 2000). De acordo com Fonseca et al (2005), após 60 dias de armazenamento a 0ºC, peras 'Rocha' produzidas no Oeste de Portugal apresentaram amadurecimento normal e uniforme, produziram aroma característico e desenvolveram textura adequada para o consumo.…”

“…Em 'd'Anjou', 'Bartlett' e 'Conference', a aplicação de etileno após a colheita ativa o amadurecimento, proporcionando frutos com textura amanteigada e aroma característico (Chiriboga et al, 2011). Em peras 'Rocha', Fonseca et al (2005) observaram que a aplicação de 100 ppm de C 2 H 4 induziu o amadurecimento dos frutos e conferiu textura adequada para o consumo, após exposição à temperatura ambiente. Contudo, a eficiência da indução do amadurecimento também irá depender do período de exposição dos frutos ao etileno (Sugar & Basile, 2013).…”