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To elucidate the physiological, biochemical and hormonal mechanisms of chilling stress mitigated by drought pretreatment, tomato seedlings (Lycopersicon esculentum cv. C.H Falat) were pretreated by 0, 10 and 20% Polyethylene glycol (PEG) for 7 days followed by subjecting to chilling stress at 3 °C for 6 days and 6 h per day. Results showed that PEG-induced drought improved growth rate of tomato seedling subjected to chilling stress and enhanced their antioxidant enzyme activity, abscisic acid (ABA), anthocyanin accumulation, potassium (K+) and proline content compared with the control (0% PEG) at the end of chilling stress period. PEG pretreatment provided significant protection against chilling stress and reduced poly phenol oxidase (PPO) activity, electrolyte leakage (EL) and H2O2 content in root and leaf of chilled seedlings. Moreover, when PEG pretreatment was applied with chilling stress, we observed an alleviation in the growth impeding and a decrease in chilling symptoms as compared to control seedlings. The highest chilling tolerance was induced by application 20% of PEG. In general, the results indicate that PEG-induced drought, by altering in some tolerant responses, could be effectively used to protect tomato’s seedling from the adverse effects of low temperatures stress.

In this study, the effects of postharvest salicylic acid, chitosan and salicyloyl chitosan treatments on chilling injury and nutritional quality of pomegranate fruits during storage at 2 °C for 5 months was investigated. Chilling injury symptoms in pomegranate fruits were manifested by external husk browning and internal segment browning. Alleviation impacts of salicyloyl chitosan treatment on pomegranate fruits chilling injury was higher than salicylic acid and chitosan treatments along, which results to delay external and internal browning and increases in electrolyte leakage. Also, pomegranate fruits treated with salicyloyl chitosan exhibited higher membrane unsaturated/saturated fatty acids (unSFA/SFA) ratio. Higher hydrophilic (H-TAA) and lipophilic (L-TAA) antioxidant capacity in pomegranate fruits treated with salicyloyl chitosan results from higher total phenols, anthocyanins and ascorbic acid accumulation. In addition to nutritional quality, pomegranate fruits treated with salicyloyl chitosan exhibited lower weight loss, respiration rate and ethylene production associated with higher firmness, total soluble solids, and titrable acidity as sensory quality. These results suggest that salicyloyl chitosan treatment can be used as promising strategy not only for alleviating chilling injury by maintaining membrane integrity results from higher unSFA/SFA ratio but also for enhancing antioxidant capacity by total phenols, anthocyanins and ascorbic acid accumulation.