Physiological and Molecular Mechanisms of ABA and CaCl2 Regulating Chilling Tolerance of Cucumber Seedlings

Cold stress is a limiting factor to the growth and development of cucumber in the temperate regions; hence, improving the crop’s tolerance to low temperature is highly pertinent. The regulation of low-temperature tolerance with exogenous ABA and CaCl2 was investigated in the cucumber variety Zhongnong 26. Under low-temperature conditions (day/night 12/12 h at 5 °C), seedlings were sprayed with a single application of ABA, CaCl2, or a combination of both. Our analysis included a calculated chilling injury index, malondialdehyde (MDA) content, relative electrical conductivity, antioxidant enzyme activities (SOD, CAT, and APX), leaf tissue structure, and expression of cold-related genes by transcriptome sequencing. Compared with the water control treatment, the combined ABA + CaCl2 treatment significantly improved the superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) of the seedlings by 34.47%, 59.66%, and 118.80%, respectively (p < 0.05), and significantly reduced the chilling injury index, relative electrical conductivity, and MDA content, by 89.47%, 62.17%, and 44.55%, respectively (p < 0.05). Transcriptome analysis showed that compared with the water control treatment, 3442 genes were differentially expressed for the combined treatment, 3921 for the ABA treatment, and 1333 for the CaCl2 treatment. KEGG enrichment analysis for both the ABA and combined ABA + CaCl2 treatments (as compared to the water control) showed that it mainly involves genes of the photosynthesis pathway and metabolic pathways. Differentially expressed genes following the CaCl2 treatment were mainly involved in plant hormone signal transduction, plant–pathogen interaction, MAPK signaling pathway–plant, phenylpropanoid biosynthesis, and circadian rhythm–plant. qRT-PCR analysis and RNA-seq results showed a consistent trend in variation of differential gene expression. Overall, this study demonstrated that although all three treatments provided some protection, the combined treatment of ABA (35 mg/L) with CaCl2 (500 mg/L) afforded the best results. A combined ABA + CaCl2 treatment can effectively alleviate cold-stress damage to cucumber seedlings by inducing physiological changes in photosynthesis and metabolism, and provides a theoretical basis and technical support for the application of exogenous ABA and CaCl2 for low-temperature protection of cucumber seedlings.

Effectiveness of CaCl2 treatment on quality attributes of banana fruit during storage

Banana is a delicious fruit with excellent nutrient components beneficial for human health. In postharvest, banana fruit is quickly ripe within few days at ambient temperature condition and its quality is seriously degraded afterwards. Extension of its stability during storage and distribution is very necessary to enhance its economic value. This research evaluated the effectiveness of CaCl2 treatment on the physicochemical quality attributes, phyto-chemical and antioxidant activities, and potential enzymes of banana fruit during storage. Banana fruits were dipped in 3% CaCl2 solution for 5 min before draining on racks for 30 min at ambient temperature to remove excess calcium chloride solution. Another banana group is dipped in clean water, leaved on racks for 30 min as the control. Both these fruit groups were then stored at 4±0.5oC with 85-90% relative humidity for 28 days. In 7 day-interval, each group is taken to verify quality attributes such as decay index, firmness, extractable juice recovery, ascorbic acid, carotenoid, total soluble solid, phenolic content, total flavonoid content, DPPH radical scavenging rate, H2O2 content, catalase (CAT) activity, superoxide dismutase (SOD) activity of banana fruit during storage. Our findings demonstrated that CaCl2 exerted a positive influence in limiting decay (2.24±0.11 mark); slowing down texture firmness reduction (7.25±0.10 N); enhancing the extractable juice recovery (85.49±1.12%); controlling ascorbic acid (12.79±0.13 mg/100 g), total soluble solid (16.40±0.13 oBrix), phenolic retention (161.35±1.19 mg GAE/100 g), flavonoid content (64.41±0.25 mg QE/100 g) and H2O2 accumulation (20.09±0.10 µmol/g); improving carotenoid (21.83±0.13 µg/100 g), catalase (15.28±0.12 U/g), superoxide dismutase activity (5.60±0.10 U/g), antioxidant capacity of banana fruit (46.20±0.15%) during chilling storage. CaCl2 treatment would be an effective approach to extend shelf life of banana fruit in commercial distribution.

Effects of CaCl2 Treatment Alleviates Chilling Injury of Loquat Fruit (Eribotrya japonica) by Modulating ROS Homeostasis

The effects of calcium chloride (CaCl2) treatment on chilling injury (CI), reactive oxygen species (ROS) metabolism, and ascorbate-glutathione (AsA-GSH) cycle in loquat fruit at 1 °C storage for 35 d were investigated. The results indicated that CaCl2 treatment remarkably suppressed the increase in browning index and firmness as well as the decrease in extractable juice rate. CaCl2 treatment also decreased the production of superoxide radical (O2•−), hydrogen peroxide (H2O2) content, but increased the 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical (OH•) scavenging ability, the activities of superoxide dismutase (SOD), catalase (CAT), and their gene expressions. Moreover, compared to the control loquat fruit, CaCl2-treated fruit maintained higher contents of AsA, GSH, higher levels of activities of ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR) and expressions of EjAPX, EjGR, EjMDHAR, and EjDHAR, but exhibited lower glutathione disulfide (GSSG) content. These results suggested that CaCl2 treatment alleviated CI in loquat fruit through enhancing antioxidant enzymes activities and AsA-GSH cycle system to quench ROS.

Effects of a Combination of 1-MCP, CaCl2 Treatment and Slow Cooling on Postharvest Physiology of ‘Zhonghuashoutao’ Peach during Storage

Effects of a combination of 1-MCP, CaCl2 treatment and slow cooling on postharvest physiology of ‘Zhonghuashoutao’ peach were investigated. Respiration rate, ethylene production, firmness, juice contents and percentage of good fruit were studied to evaluate the quality of peach. The results showed that 1-MCP, CaCl2 treatment reduced the amount of respiration rate and ethylene production, delayed the appearence of ethylene peak, prolonged softening, restrained the chilling injury of ‘Zhonghuashoutao’ peach after harvest. Slow cooling method had better effect and could delay the incidence of physiological disorder and maintained good quality during storage.