Plants experiencing salt-induced stress often reduce cytokinin levels during the early phases of stress-response. Interestingly, we found that the cytokinin content in the apple rootstock "robusta" was maintained at a high level under salt stress. Through screening genes involved in cytokinin biosynthesis and catabolism, we found that the high expression levels of IPT5b in robusta roots were involved in maintaining the high cytokinin content. We identified a 42 bp deletion in the promoter region of IPT5b, which elevated IPT5b expression levels, and this deletion was linked to salt tolerance in robusta×M.9 segregating population. The 42 bp deletion resulted in the deletion of a Proline Response Element (ProRE), and our results suggest that ProRE negatively regulates IPT5b expression in response to proline. Under salt stress, the robusta cultivar maintains high cytokinin levels as IPT5b expression cannot be inhibited by proline due to the deletion of ProRE, leading to improve salt tolerance.
The effects of hot air flow (HAF) treatment on the postharvest storage of ‘Newhall’ navel oranges were investigated in this study. Studies were conducted with two separate sections. First of all, the effects of HAF at 37 °C for 36 h, for 48 h, and for 60 h were tested on fruit decay and weight loss. Thus, the optimal treatment was found as HAF at 37 °C for 48 h based on the fruit decay percentage and weight loss, and further studies were carried out with this treatment. The HAF-treated and control fruits were flowed at 37 °C and 20 °C with relative humidity (RH) of 85–95% for 48 h, respectively. After flowing, fruits of both treatments were individually film-packed, precooled (10–12 °C, 12 h), and stored (6 ± 0.5 °C and 85–90% relative humidity) for 120 days. Regular (0, 15, 30, 45, 60, 90, and 120 days) measurements were carried out for analyzing total soluble solid (TSS) content, titratable acid (TA) content, vitamin C (VC) content, total sugar content, respiration rate, malondialdehyde (MDA) content, and protective enzyme activities. The results indicated that HAF treatment significantly inhibited the MDA content and respiration rate of navel orange fruits after 45 d storage. The superoxide dismutase (SOD) and peroxidase (POD) enzyme activities were enhanced after 60 d storage, while polyphenol oxidase (PPO) enzyme activities were enhanced throughout the storage period. Results suggested that the SOD and POD activities are highly related with respiratory activities and could be enhanced with hot air flow. Meanwhile, HAF treatment maintained high content of TSS, total sugar, TA, and VC.
In plants, the Gretchen GH3 (GH3) protein is involved in free auxin (IAA) and amino acid conjugation, thus controlling auxin homeostasis. To date, many GH3 gene families have been identified from different plant species. However, the GH3 gene family in kiwifruit (Actinidia chinensis) has not been reported. In this study, 12 AcGH3 genes were identified, phylogenetic analysis of AtGH3 (Arabidopsis), SlGH3 (Solanum lycopersicum), and AcGH3 provided insights into various orthologous relationships among these proteins, which were categorized into three groups. Expression analysis of AcGH3 genes at different postharvest stages suggested limited or no role for most of the AcGH3 genes at the initiation of fruit ripening. AcGH3.1 was the only gene exhibiting ripening-associated expression. Further study showed that the expression of AcGH3.1 gene was induced by NAA (1-naphthylacetic acid, auxin analogue) and inhibited by 1-MCP (1-methylcyclopropene, ethylene receptor inhibitor), respectively. AcGH3.1 gene silencing inhibited gene expression and delayed fruit softening in kiwifruit. The results indicate that AcGH3.1 may play an important role in the softening process of fruits. Analysis of the AcGH3.1 promoter revealed the presence of many cis-elements related to hormones, light, and drought. The determination of GUS (β-Galactosidase) enzyme activity revealed that promoter activity increased strikingly upon abscisic acid (ABA), ethylene, or NAA treatment, and significantly decreased with salicylic acid (SA) treatment. The present study could help in the identification of GH3 genes and revelation of AcGH3.1 gene function during postharvest stages, which pave the way for further functional verification of the AcGH3.1 gene.
This work investigates the role of hydrogen sulfide (H2S) in the browning and regulating the antioxidant defensive system in fresh-cut Chinese water chestnuts. The samples were fumigated with 0, 10, and 15 μl L−1 of H2S and stored at 10°C for 8 days. The results indicated that the H2S treatment significantly inhibited the browning of fresh-cut Chinese water chestnuts, reduced superoxide anion (O2·-) production rate and H2O2 content accumulation, promoted the increase of total phenol content, and enhanced activities of catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) (P < 0.05). On the other hand, phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) activities remained at a low level in the H2S treatment (P < 0.05). This result suggested that H2S treatment might be a promising approach to inhibit browning and prolong the shelf life by enhancing oxidation resistance and inhibiting browning enzyme activity of fresh-cut Chinese water chestnuts during storage. Among them, the 15 μl L−1 H2S treatment had the best effect on fresh-cut Chinese water chestnuts.
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