Introduction
The purpose of commercial storage of fruit is to lengthen shelf-time and maintain the taste of pulp. The current postharvest storage technologies mainly focus on a combined utilization of storage environment factors such as temperature, modified atmosphere and chemicals, and among them temperature control is the most widely used method for fruits and vegetables during shelf life. Although cold conditioning is a virtually irreplaceable method used to prolong the postharvest quality of horticultural products, chilling injury (CI) is triggered in tropical and subtropical fruits which are sensitive to low temperature (Teklehaimanot, 2004). CI plants have a series of cellular changes, including ethylene synthesis, membrane fluidity and cytoskeletal rearrangement, resulting in internal browning (IB), flesh breakdown, lack of juiciness, and loss of flavor, which seriously affects the commercial values of fruits (Cramer et al., 2011).
With the climatic change of global warming, high temperature stress becomes a major plant stress affecting plant cellular homeostasis, crop growth and development (Tubiello et al., 2007). Plants have evolved a series of responses to raised temperature linked with heat stress proteins (HSPs), heat stress factors (HSFs), and phytohormones such as abscisic acid (ABA), salicylic acid (SA) and ethylene (Kotak et al., 2007). Besides, the effects of high temperature have been reviewed on its inhibition of ethylene production, control of postharvest diseases and reducing CI in many fruits and vegetables (Barkaigolan and Phillips, 1991; Lurie, 1998; 2005). In kiwifruit, high temperature stress controls fruit ripening by inhibiting ethylene production and signaling sensitivity (Antunes and Sfakiotakis, 2000), similar to studies on apple (Lurie and Klein, 1990) and tomato (Lurie and Klein, 1991). However, decline of fruit firmness and increase of ethylene production were observed for banana fruit during storage at high temperature (Yan et al., 2011). Overall, numerous studies focused on how to reduce CI and on the effect of heat treatment on ethylene metabolism, all of which showed that temperature is vital to fruit storage. However, limited studies have considered the influences of high temperature for shelf life after transient cold conditioning.
Peach (Prunus persica L. Batsch) has highly perishable fruits that decay quickly at ambient temperature. Although refrigeration is used to maintain flesh quality and prolong shelf-time, peach is highly sensitive to low temperature, resulting in CI. The major symptoms of postharvest CI are internal browning, mealiness or wooliness, and flesh bleeding or internal reddening with physiological disorders (Brummell et al., 2004; Lurie and Crisosto, 2005). In previous studies, heat treatment has been applied prior to cold storage to prevent or alleviate CI by acquiring CI tolerance in response to heat shock (Saltveit, 1991; Ferguson et al., 2000; Paull and Chen, 2000; Budde et al., 2006; Wang et al., 2006; Peng et al., 2009; Zhang et al., 2011). However, information is much less about high temperature conditioning after cold treatment in peach fruits.
In this study, we performed comparative transcriptomic analysis of postharvest peach fruits between high temperature (HT: 35 °C) and common temperature (CT: 25 °C) after a pre-storage at 5 °C for 2 days, and combined the comparison results with measured physiological changes to comprehend the process of peach fruit decay. This study provided new insights into the molecular mechanisms of temperature response during fruit shelf life and offered novel clues for developing the fruit storage technologies in practice.