Postharvest nitric oxide treatment induced the alternative oxidase pathway to enhance antioxidant capacity and chilling tolerance in peach fruit.

Nitric oxide (NO) is an important regulator of plant response to cold stress. In this study, NO treatment delayed the development of chilling injury (CI), inhibited the increase in H2O2 content, O2- production rate and decrease in firmness of postharvest peach fruit. Meanwhile, through RNA-seq analysis, NO treatment up-regulated gene expression of PpG-6-PDH, Pp6-PGDH and PpAOX while it down-regulated the expression of PpGPI and PpHK, suggesting that the pentose phosphate respiratory pathway and cyanide-resistant respiratory pathway were promoted and the glycolysis pathway was inhibited. Furthermore, the PpAOX expression was consistent with the trend of PpPOD1/2 expression and H2O2 content, indicating that AOX may play a role in reducing oxidative damage of peach fruit by scavenging H2O2. Thus, it was concluded that NO treatment could induce the cyanide-resistant respiration pathway to enhance antioxidant ability and chilling tolerance in post-harvest peach fruit.

Salicylic acid treatment mitigates chilling injury in peach fruit by regulation of sucrose metabolism and soluble sugar content.

Peach fruit stored in the cold are susceptible to chilling injury. A pre-storage treatment with the natural hormone salicylic acid can alleviate chilling damage, although the mechanism is unclear. We found that a treatment with 1 µmol L-1 salicylic acid for 15 min prior to storage at 4 °C delayed and reduced fruit internal browning, a symptom of chilling injury. Salicylic acid had a large effect on sugar metabolism, increasing total soluble sugars via a substantial increase in sucrose content. The transcript abundance of genes related to sucrose biosynthesis and degradation was significantly regulated by salicylic acid, consistent with the changes in sucrose content. Salicylic acid treatment also increased the expression of two DREB cold stress-related proteins, transcriptional activators that regulate cold resistance pathways. The results show that salicylic acid alleviates chilling injury in peach by multiple mechanisms, including an increased content of sucrose and activation of cold response genes.

Jasmonic acid treatment alleviates chilling injury in peach fruit by promoting sugar and ethylene metabolism.

Peach (Prunus persica L.) fruit are highly susceptible to chilling injury during cold storage, resulting in internal flesh browning and a failure to soften normally. We have examined the effect of a postharvest treatment consisting of a brief (30 s) dip in the natural plant hormone jasmonic acid, prior to storage at 4 °C. Jasmonic acid treatment reduced the severity of internal flesh browning and did not inhibit fruit softening over a 35 d storage period. Two major physiological effects of jasmonic acid on the fruit were observed, an increase in ethylene production and a prevention of the decline in soluble sugar content seen in controls. An increased soluble sugar content may have multiple benefits in resisting chilling stress, scavenging reactive oxygen species and acting to stabilize membranes. Our results show that a treatment with jasmonic acid can enhance chilling tolerance of peach fruit by regulating ethylene and sugar metabolism.

Melatonin treatment reduces ethylene production and maintains fruit quality in apple during postharvest storage.

The effects of treatment with melatonin on ripening of 'Fuji' apples during storage at 1 °C for 56 d were investigated. The apples were harvested at the commercial ripening stage and treated with 1 mmol L-1 melatonin. Compared with the control, melatonin treated apples had significant reduced ethylene production (28 d-56 d) and weight loss (14 d-56 d) during storage (p < 0.05). Also, the melatonin treatment maintained better apple skin structure throughout storage. The reduced ethylene production was regulated by the decreased expressions of MdACO1, MdACS1, MdAP2.4 and MdERF109, based on RNA-Seq analysis, which was validated using qRT-PCR analysis. Moreover, the activity of 3 enzymes, including peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), were significantly increased in melatonin treated fruit (p < 0.05). Taken together, this study highlights the inhibitory effects of melatonin in ethylene biosynthesis and factors influencing postharvest quality in apple.

Combined transcriptomic and proteomic analysis of cold stress induced sugar accumulation and heat shock proteins expression during postharvest potato tuber storage.

Plant species differ greatly in their ability to acclimatise to and survive, cold stress. Normally, potato tubers are stored at low temperatures (below 10 °C) to delay sprouting. In this research, combined transcriptomic and proteomic analysis was conducted on potato tubers stored at 15 °C, 4 °C and 0 °C to investigate the mechanism of cold responses during postharvest storage. Results showed that soluble sugars were accumulated under low temperatures, regulating by granule-bound starch synthase 1, beta-amylase, invertase inhibitor and fructokinase. In addition, fifteen heat shock proteins (Hsps), including three Hsp70s, two Hsp80s, one Hsp90, one Hsp100 and eight small Hsps, were induced by low temperatures, which may act individually or synergistically to prevent physiological or cellular damage from cold stress in postharvest potato tubers. This research provided general information of sugar accumulation and defense response in potato tuber under cold storage.

UV-C treatment promotes quality of early ripening apple fruit by regulating malate metabolizing genes during postharvest storage.

Early ripening apples are usually used for fresh marketing because of short storage life, although they are with high acid and low sugar contents. Understanding the malate metabolism in fleshy fruit and underpinning process during ripening is crucial for particular crop improvement where acidity is a concern for direct consumption or further processing. In this research, a traditional Chinese apple cultivar 'Hongyu', which belongs to early ripening apple cultivar, were freshly harvested at commercial maturity stage (120 Days after full bloom) and used for different storage temperature (4°C, 20°C) and UV-C treatment (following storage at 20°C after treatment). Simple sugars (glucose, sucrose, and fructose) and organic acids (malic, and oxalic) were assessed after 14 d of storage. Compared to fruits stored at 20°C, the malate content in fruits stored at 4°C significantly higher, while it was decreased significantly in UV-C treated fruits stored at 20°C after 14 d of storage. The sugar content was almost similar throughout the UV-C-treated fruits and fruits stored at different temperature. The higher ratios of total sugars to total organic acids in UV-C treated fruits after 14 d suggest that UV-C treatment has the potential to improve the taste of early ripening apple cultivars. Considering the significant difference in malate the samples at 14 d of storage were subjected for RNA-seq analysis. Transcriptome analysis revealed that the phenomena underlying this change were governed by metabolism of malate by the regulation of NADP-malic enzyme (NADP-ME) and phosphoenolpyruvate carboxylase kinase (PEPCK) in apple during postharvest storage. This transcriptome profiling results have specified the transcript regulation of malate metabolism and lead to possible taste improvement without affecting the other fruit quality attributes.

Effects of (S)-Carvone and Gibberellin on Sugar Accumulation in Potatoes during Low Temperature Storage.

Potato tubers (Solanum tuberosum L.) are usually stored at low temperature, which can suppress sprouting and control the occurrence of diseases. However, low temperatures lead potatoes to easily suffer from cold-induced sweetening (CIS), which has a negative effect on food processing. The aim of this research was to investigate potential treatments on controlling CIS in potatoes during postharvest storage. "Atlantic" potatoes were treated with gibberellin and (S)-carvone, respectively, and stored at 4 °C for 90 days. The results showed that gibberellin can significantly accelerate sprouting and sugar accumulation by regulating expressions of ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase (GBSS), ß-amylase (BAM1/2), UDP-glucose pyrophosphorylase (UGPase) and invertase inhibitor (INH1/2) genes. The opposite effects were found in the (S)-carvone treatment group, where CIS was inhibited by modulation of the expressions of GBSS and INH1/2 genes. In summary, gibberellin treatment can promote sugar accumulation while (S)-carvone treatment has some effects on alleviating sugar accumulation. Thus, (S)-carvone can be considered as a potential inhibitor of some of the sugars which are vital in controlling CIS in potatoes. However, the chemical concentration, treatment time, and also the treatment method needs to be optimized before industrial application.