ABSTRACT
Hippeastrum papilio (Amaryllidaceae) is a promising new source of galanthamine - an alkaloid used for the cognitive treatment of Alzheimer's disease. The biosynthesis and accumulation of alkaloids are tissue - and organ-specific. In the present study, histochemical localization of alkaloids in H. papilio's plant organs with Dragendorff's reagent, revealed their presence in all studied samples. Alkaloids were observed in vascular bundles, vacuoles, and intracellular spaces, while in other plant tissues and structures depended on the plant organ. The leaf parenchyma and the vascular bundles were indicated as alkaloid-rich structures which together with the high proportion of alkaloids in the phloem sap (49.3% of the Total Ion Current - TIC, measured by GC-MS) indicates the green tissues as a possible site of galanthamine biosynthesis. The bulbs and roots showed higher alkaloid content compared to the leaf parts. The highest alkaloid content was found in the inner bulb part. GC-MS metabolite profiling of H. papilio's root, bulb, and leaves revealed about 82 metabolites (>0.01% of TIC) in the apolar, polar, and phenolic acid fractions, including organic acids, fatty acids, sterols, sugars, amino acids, free phenolic acids, and conjugated phenolic acids. The most of organic and fatty acids were in the peak part of the root, while the outermost leaf was enriched with sterols. The outer and middle parts of the bulb had the highest amount of saccharides, while the peak part of the middle leaf had most of the amino acids, free and conjugated phenolic acids.
Subject(s)
Alkaloids , Amaryllidaceae , Galantamine , Plant Extracts , Cholinesterase Inhibitors/chemistry , Fatty Acids , SterolsABSTRACT
MAIN CONCLUSION: The polyploidization of Hippeastrum papilio influences its primary and secondary metabolism including the biosynthesis of bioactive alkaloids. Hippeastrum papilio is an ornamental plant that has advantages in comparison to the currently used plants for the extraction of galanthamine, a natural compound used for the cognitive treatment of Alzheimer's disease. In the present study, an autotetraploid line of H. papilio was induced for the first time, after treatment with 0.05% colchicine for 48 h. The chromosome number in diploids was found to be 2n = 2x = 22 and for autotetraploids 2n = 4x = 44. The flow cytometric analyses detected a DNA C-value of 14.88 ± 0.03 pg (1C) in diploids and 26.57 ± 0.12 pg in autotetraploids. The morphological, cytological, and phytochemical studies showed significant differences between diploids and autotetraploids. The length and width of stomata in autotetraploids were 22.47% and 17.94%, respectively, larger than those observed in the diploid leaves. The biomass of one-year-old autotetraploid H. papilio plants was reduced by 53.99% for plants' fresh weight, 56.53% for leaves' fresh weight, and 21.70% for bulb diameter. The GC-MS analysis of methanol extracts from one-year-old diploid and autotetraploid H. papilio plants revealed over 60 primary and secondary metabolites including alkaloids, phenolic acids, sterols, saccharides, and alcohols, among others. Principal component analysis of the metabolite profiles indicates a divergence of the metabolism between diploid and autotetraploid plants. The content of galanthamine and haemanthamine was found to be 49.73% and 80.10%, respectively, higher in the leaves of autotetraploids, compared to the diploid ones. The biosynthesis of the saccharides shows a tendency to be upregulated in tetraploid plants, while that of phenolic acids was downregulated. Polyploidization of H. papilio creates possibilities for further crop improvement aimed at high-galanthamine-producing genotypes.
