Seasonal variation in alkaloid content, phenolic constituent and biological activities of some Leucojum aestivum L. populations in Turkey

Abstract

Summer snowflake (Leucojum aestivum L.), a bulbous plant in the Amaryllidaceae family, is a well-known source of two pharmaceutically significant alkaloids: galanthamine that is used to treat Alzheimer's disease and lycorine that has potent antiviral properties, especially against SARS-CoV-2 (COVID-19). Environmental factors such as temperature, light, soil, and so on, as well as harvest time and plant parameters such as genotype and plant parts, all have a quantitative and qualitative impact on secondary metabolite production such as alkaloids and phenols. This study hypothesized that different populations (genotype), growing seasons, environmental temperature and soil type can change the alkaloid (galanthamine and lycorine) and phenolic content, and biological activities (antioxidant and antibacterial) in the bulbs and leaves of this plant. Summer snowflakes were collected from 6 different locations in Turkey (Gölcük-Bolu, Yeniçağa-Bolu, Kaynarca-Sakarya, Delmece-Yalova, Uluabat-Bursa and Terkos-İstanbul) at 3 different growing periods (vegetative, reproductive and ripening). Methanol extract of the plant parts were quantitatively analyzed for their alkaloid content with HPLC-DAD, and for their antioxidant capacity and total phenol-flavonoid content with spectrophotometric determination. Besides, antibacterial activity was investigated with disc diffusion assay. The locations of Delmece-Yalova and Gölcük-Bolu provided galanthamine-rich population and optimal growing conditions for the cultivation of this species. Generally, vegetative and ripening periods were the most effective in alkaloid production. But, phenolic content accumulation was unrelated to the growing seasons. Higher temperatures in the bulbs and lower temperatures in the leaves supported the galanthamine and lycorine production. It was noticeable that alkaloid and total phenol accumulation in the bulbs showed similar tendency in that the highest temperature caused the highest alkaloid levels and phenolic content. Also, neutral to slightly alkaline soils with high organic matter content were effective in enhancing the alkaloid content and phenolic constituents. Moderate antioxidant activity and no antibacterial potential were observed with L. aestivum. The results found can be a guide for revealing the best population and environmental conditions for the cultivation of this plant, as well as showing the correct harvest time for bulbs and leaves to get the best galantamine and lycorine content.