Hydrogen Sulfide Delays Postharvest Senescence and Plays an Antioxidative Role in Fresh-cut Kiwifruit

Hydrogen sulfide (H2S) was recently recognized as an endogenous gaseous molecule involved in seed germination, root organogenesis, abiotic stress tolerance, guard cell movement, and delay of senescence in plants. In the present study, we show that H2S participates in the regulation of postharvest ripening and senescence in fresh-cut kiwifruit, Actinidia deliciosa. Fumigation of fresh-cut kiwifruit with the H2S donor sodium hydrosulfide (NaHS) solution prolonged kiwifruit storage time and alleviated senescence and tissue softening in a dose-dependent manner at an optimal concentration of 1.0 mmol·L NaHS. H2S treatment maintained higher levels of reducing sugars, soluble proteins, free amino acids, ascorbate, and chlorophyll and lowered carotenoid levels. H2S treatment also significantly decreased the contents of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide anion (O2 ) during fruit storage compared with water controls. Furthermore, the activities of guaiacol peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were increased by H2S treatment, whereas the activity of lipoxygenase (LOX) was decreased compared with untreated controls. Taken together, these results suggest that H2S is involved in prolonging postharvest shelf life and plays an antioxidative role in fresh-cut kiwifruit. H2S has been identified as a third gasotransmitter after nitric oxide (NO) and carbon monoxide (CO) in animals (Wang, 2002; Yang et al., 2008). Accumulating evidence now shows that H2S plays various physiological roles in plants, including regulating seed germination, root organogenesis, abiotic stress tolerance, photosynthesis, and guard cell movement, implying that H2S acts as an important gaseous regulator (Chen et al., 2011; Garcı́aMata and Lamattina, 2010; Hancock et al., 2011; Rausch and Wachter, 2005; Shan et al., 2012; Zhang et al., 2008, 2009). In our previous studies, we presented evidence supporting a role of H2S in delaying senescence of cut flowers and prolonging vase life in a wide spectrum of botanical species including herbaceous and woody plants, suggesting that the characteristic of H2S might be universal in plant senescence (Zhang et al., 2011). More recently, H2S was found to play an antioxidative role in prolonging postharvest shelf life of strawberry, which is a nonclimacteric fruit (Hu et al., 2012). Much less research has been carried out on the fruits of woody plants where the physiological role of H2S in prolonging shelf life of these fruits is poorly understood. Kiwifruit is classified as a climacteric fruit as a result of its high sensitivity to ethylene (Pranamornkith et al., 2012). Kiwifruit has become a product of interest as a result of its high level of ascorbate (vitamin C) as well as high concentrations of many types of mineral elements. Harvested kiwifruit undergoes a rapid rise in respiration rate after a week in storage, leading to a short shelf life under ambient conditions. Growers have therefore investigated the effectiveness of treatments that potentially extend the shelf life of kiwifruit, including application of pharmacological agents such as 1-methylcyclopropene (Jhalegar et al., 2011). It is believed that oxidative damage is one cause of the short shelf life of postharvest fruits (Hu et al., 2012). Among the naturally occurring compounds that have been shown to protect kiwifruit from oxidative damage caused by a reactive oxygen species (ROS) burst during storage is NO (Zhu et al., 2008). We have found that H2S plays an antioxidative role in delaying senescence in various species of cut flowers and nonclimacteric fruits such as strawberry (Hu et al., 2012; Zhang et al., 2011), leading us to investigate the possibility that H2S has similar effects on the senescence of postharvest climacteric fruits such as kiwifruit. We demonstrate that H2S extended the shelf life of fresh-cut kiwifruit, probably through the up-regulation of antioxidant enzymes. Materials and Methods Plant materials and treatments. Kiwifruit (Actinidia deliciosa) used in this work was supplied by a fruit market in Hefei, Anhui province, China. Fruit harvested in the same day with similar size and maturity (80%) were selected in the morning and transported to the laboratory within 2 h. Kiwifruit without physical damage and microbial and insect infections were selected for experiments. Fruit were cut into eight pieces of the same size and weight, and H2S was applied through the H2S donor NaHS (Sigma, St. Louis, MO). Aqueous NaHS solutions (150 mL) at 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, or 1.75 mmol·L were prepared in sealed containers (volume 3 L) and the eight cut pieces from eight different kiwifruit were exposed to H2S gas released from NaHS solution in the sealed containers. The storage temperature was 20 ± 0.5 C and the relative humidity was 85% to 90%. NaHS solutions were renewed daily and the kiwifruit were observed for every 24 h. The experiment was repeated for three fruit seasons and a similar phenomenon was observed. Rot classification of fruits. Eight pieces of kiwifruit were used in each treatment for rot classification. Fruits were classified in four ranks according to the percentage of rotten surface area: 1 = rot surface less than 10%; 2 = rot surface between 10% and 30%; 3 = rot surface between 30% and 50%; and 4 = rot surface more than 50%. The rot classification was recorded everyday. The experiment was repeated three times. Determination of fruit firmness. Fruit firmness was measured at the equatorial part of each fresh-cut kiwifruit pieces by a 5-mm diameter flat probe with a texture analyzer (Model TA XT plus; SMS). The penetration depth was 5 mm and the cross-head speed was 5 mm·s. Fruit firmness values were an average of 8 kiwifruit pieces ± SD. The experiment and following ones were repeated three times. Determination of malondialdehyde, hydrogen peroxide, and superoxide anion. The contents of MDA, H2O2 and O2 – were determined by the procedures described by Zhang et al. (2010a). Fruit samples (5.00 ± 0.05 g) Received for publication 28 May 2013. Accepted for publication 9 Sept. 2013. Funding for this work was provided by the National Natural Science Foundation of China (31301820, 31271803, 31300133), the Scientific Research Foundation for Returned Overseas Chinese Scholars (SRF for ROCS, SEM), the Natural Science Foundations of Anhui Province (11040606M85), and the Anhui Provincial Education Department (2012AJZR0028, ZD200910). We gratefully acknowledge the contributions of Russell L. Jones on the revision of the manuscript. These authors contributed equally to this work. To whom reprint requests should be addressed; e-mail hzhanglab@gmail.com. HORTSCIENCE VOL. 48(11) NOVEMBER 2013 1385 | POSTHARVEST BIOLOGY AND TECHNOLOGY