Analysis of the cuticular wax composition and ecophysiological studies in an arid plant - Ziziphus nummularia (Burm.f.) Wight & Arn.

Plants in arid regions are exposed to various abiotic stresses and the presence of the waxy cuticular layer acts as a defensive barrier, which consists mainly of long chain fatty acids, hydrocarbons and other derived compounds. Studies on the chemical composition and properties of cuticles of arid plants are scanty. The present study deals with the analysis of cuticular wax composition and effect of temperature on some ecophysiological parameters of an important arid plant Ziziphus nummularia. A total of 59 different wax compounds were detected from the leaf cuticle by capillary GC-MS. 4-Hydroxycyclohexanone, Heptacosane and 2,7-Dimethyloctane-3,5-dione were the dominant wax compounds in Z. nummularia. The variation of photosynthetic rate varied from 0.70 to 7.70 µmol CO2 m-2s-1 against the studied temperature range of 15-55 °C. The transpiration rate varies from 1.80 to 8.40 mmol H2O m-2s-1 within the temperature range of 15-55 °C. The quantum yield of photosystem II (Fv/Fm) also exhibited much variation due to the variation of temperature. The results clearly shows that Z. nummularia is highly adapted to restrict water loss and can tolerate high temperatures and can be considered as an appropriate species for vegetating the arid areas.

Physiological and biochemical responses to aluminum-induced oxidative stress in two cyanobacterial species.

Phycoremediation technologies significantly contribute to solving serious problems induced by heavy metals accumulation in the aquatic systems. Here we studied the mechanisms underlying Al stress tolerance in two diazotrophic cyanobacterial species, to identify suitable species for Al phycoremediation. Al uptake as well as the physiological and biochemical responses of Anabaena laxa and Nostoc muscorum to 7 days Al exposure at two different concentrations i.e., mild (100 µM) and high dose (200 µM), were investigated. Our results revealed that A. laxa accumulated more Al, and it could acclimatize to long-term exposure of Al stress. Al induced a dose-dependent decrease in photosynthesis and its related parameters e.g., chlorophyll content (Chl a), phosphoenolpyruvate carboxylase (PEPC) and Ribulose‒1,5‒bisphosphate carboxylase/oxygenase (RuBisCo) activities. The affect was less pronounced in A. laxa than N. muscorum. Moreover, Al stress significantly increased cellular membrane damage as indicated by induced H2O2, lipid peroxidation, protein oxidation, and NADPH oxidase activity. However, these increases were lower in A. laxa compared to N. muscorum. To mitigate the impact of Al stress, A. laxa induced its antioxidant defense system by increasing polyphenols, flavonoids, tocopherols and glutathione levels as well as peroxidase (POX), catalase (CAT), glutathione reductase (GR) and glutathione peroxidase (GPX) enzymes activities. On the other hand, the antioxidant increases in N. muscorum were only limited to ascorbate (ASC) cycle. Overall, high biosorption/uptake capacity and efficient antioxidant defense system of A. laxa recommend its feasibility in the treatment of Al contaminated waters/soils.

Identification, Bioactivity, and Productivity of Actinomycins from the Marine-Derived Streptomyces heliomycini.

In the process of profiling the secondary metabolites of actinobacteria isolated from the Saudi coastal habitats for production of antibiotics and anti-cancer drugs, the cultures of strain WH1 that was identified as Streptomyces heliomycini exhibited strong antibacterial activity against Staphylococcus aureus. By means of MS and NMR techniques, the active compounds were characterized as actinomycins X0ß, X2, and D, respectively. The research on the productivity of this strain for actinomycins revealed that the highest production of actinomycins X0ß, X2, and D was reached in the medium MII within 5% salinity and pH 8.5. In this optimized condition, the fermentation titers of actinomycins X0ß, X2, and D were 107.6 ± 4.2, 283.4 ± 75.3, and 458.0 ± 76.3 mg/L, respectively. All the three actinomycins X0ß, X2, and D showed potent cytotoxicities against the MCF-7, K562, and A549 tumor cell lines, in which actinomycin X2 was the most active against the three tumor cell lines with the IC50 values of 0.8-1.8 nM. Both actinomycins X2 and D showed potent antibacterial activities against S. aureus and the methicillin-resistant S. aureus, Bacillus subtilis, and B. cereus and the actinomycin X2 was more potent.