Search

Salinity is one of the most important abiotic stresses that significantly decreases the productivity of agricultural crops. Melatonin (MT) acts as an antioxidant and plays a vital role in overcoming oxidative damage. However, previous literature has not provided a clear understanding of the impact of MT on lettuce plants under salinity stress. So, we investigated the effect of exogenous MT at 0 μM, 50 μM, 100 μM and 150 μM on lettuce plants grown under salinity stress (0 mM NaCl, 50 mM NaCl and 100 mM NaCl) with respect to vegetative growth, photosynthetic pigments, relative water content (RWC), electrolyte leakage (EL), malondialdehyde (MDA), H2O2, O2•- and antioxidants enzymes. Results showed that NaCl stress significantly decreased vegetative growth, RWC and photosynthetic pigments and in contrast enhanced dry matter, EL, MDA, H2O2, O2•-, Na+, Cl-, peroxidase (POD), superoxide dismutase (SOD) and glutathione reductase (GR) of lettuce plants compared to non-salinized control. The results demonstrated that under salinity conditions, foliar applications of MT significantly alleviated the harmful effects of salinity and increased number of leaves, leaf area, fresh weight, chlorophyll (a), chlorophyll (b), total chlorophyll, carotenoids and RWC in comparison to untreated plants (control). Meanwhile, dry matter, MDA, H2O2, O2•-, Na+, Cl-, POD, SOD and GR were significantly decreased compared to untreated lettuce plants. In this respect, spraying MT at 150 μM ranked the first, then 100 μM, compared to the lower concentration (50 μM). In conclusion, MT application can be used to alleviate harmful effects of salinity stress.

The reduction in shelf-life and nutritional value of cauliflower florets are the most vital problems during cold storage. This research was performed to explore the impact of the pre-harvest foliar implementation of proline (PR), methionine (MT), and melatonin (ML), at a rate of 25 mg.L-1, on shelf-life and active composites of cauliflower florets (cv. 'Arasya') stored at 10 °C for 14 d. The obtained results exhibited that florets from treated plants with PR, MT, and ML were lower in water loss, electrolyte leakage, browning index, and titratable acidity (TA) compared with untreated plants, at the end of storage. Furthermore, these pre-harvest treatments significantly slow down the loss of total sugar content, reducing sugar, total soluble solid (TSS), glucosinolates concentration (Gly), total phenols (TP), vitamin C (VC), and antioxidant activity (DPPH) than control samples. After 14 days of storage, the application of PR, MT, and ML significantly improved the activity levels of phenylalanine ammonia-lyase (PAL), and catalase (CAT) as well as declined the polyphenol oxidase (PPO), peroxidase (POD) activates in the florets during the cold storage. Therefore, the pre-harvest application of PR, MT, and ML might be promising substances to keep the nutritional quality of cauliflower forests and reduce the browning index during cold storage. [ABSTRACT FROM AUTHOR]