Effects of environmental factors on growth, bioactive compounds and cholinergic properties of hydroponically raised salvia and narcissus species

Abstract

The increasing interest of the pharmaceutical and food industry in exploiting natural products has initiated scientific studies on the so-called aromatic & medicinal plants. However, information regarding their cultivation is scarce, and as bioactive phytochemicals are highly susceptible to environmental regulation, optimization and full control of growth conditions are vital for a cost-effective, standardised and high-quality medicinal product. Thus, Salvia officinalis var purpurea and Narcissus "Ice Follies" were cultivated by means of the hydroponic Nutrient Film Technique (NFT), under various nutrient conditions i. e. nitrate (N-NO3), phosphorus (P) and various electrical conductivity (EC) regimes. Essential oils from S. officinalis and the alkaloid galanthamine from Narcissus sp. possess cholinergic activities relevant to the symptomatic treatment of Alzheimer's disease (AD). This study aimed to determine optimum growth conditions for enhanced plant biomass accumulation and improved yield and quality of the bioactive compounds in order to increase the efficacy of the medicinal species. In addition, anti-cholinesterase properties of S. officinalis var purpurea were investigated. At the end of each experiment plant biomass accumulation, root to shoot investment, plant height, leaf area and photosynthetic pigments were assessed together with uptake of nitrates, phosphorus, potassium and calcium. Essential oils of sage and alkaloids from Narcissus were obtained via steam distillation and organic solvent extraction method respectively. Oils were subsequently analysed by means of gas chromatography mass spectroscopy, whereas high performance liquid chromatography was employed for alkaloid analysis. Cholinesterase inhibition was tested via the colorimetric Ellman's enzyme assay. S. officinalis and Narcissus species were successfully cultivated in the NFT, for the very first time. In Salvia optimum conditions for high shoot biomass production appeared to be the 150 mg/L N-N03,12 mg/L P supply and EC 1.8 mS/cm. Nitrate level marginally affected growth or ontogeny of Narcissus, however alkaloid yield was significantly augmented by N-N03 supply (180 mg/L) and exhibited much higher values in comparison with the existing literature. In contrast, Salvia essential oils revealed weak responses to N-NO3 and P nutrition in terms of yield and quality, whereas high EC levels considerably altered oil relative composition. Essential oil content was approximately 11%w hilst a report for S. officinalis raised in Britain indicated only 0.53%. Camphor and a-caryophyllene were abundant in the oil comprising ca the 10-17% and 16-23% respectively. a-Thujone contributed for 9-10%. All other constituents like apha and beta pinene, 1.8 cineole, ledol, borneol and bornyl acetate appeared with concentrations less than 4% in the oil mixture. Anti-cholinesterase activity of the essential oils was dual and remained unchanged under all growth conditions exhibiting relatively low IC50 values; approximately 0.055 to 0.07 mg/ml for human acetylcholinesterase (AChE) and 0.07 mg/ml for butyrylcholinesterase (BuChE) enzyme from horse serum that was time-dependant. Competitive type of inhibition was revealed for AChE and non-competitive for BuChE. Finally, the ethanolic extracts of S. officinalis var purpurea preferentially inhibited BuChE with IC50 significantly lower than the oil i. e. 0.054 mg/ml. The findings of this project demonstrated that NFT is an important means for successful cultivation of Salvia and Narcissus species. N-NO3, P and EC levels significantly affected growth of Salvia and EC conditions altered essential oil composition. The yield of galanthamine in bulbs and leaves of Narcissus was significantly augmented by N-NO3 supply. Therefore, standardisation of cultivation methods for medicinal species is essential to assure biochemical consistency and quality. S. officinalis var purpurea should be considered as an alternative strategy for the treatment of mild to moderate AD.