Stress conditions during plant growth increase the anti-herpetic properties of Lilium candidum leaf extracts and fractions

When submitted to stress conditions during growth, plants modify their secondary metabolites production, which could increase therapeutic properties. Lilium candidum is a beautiful plant with potent antiviral activity, growing wild in the Middle East. We investigated the effect of biotic and abiotic stress applied on L. candidum plants during their growth, on the anti-herpetic efficiency of leaf ethanolic extracts and their fractions against herpes simplex virus (HSV) 1 in vitro. Ethanolic leaf extracts were collected from L. candidum leaves of healthy plants growing under regular conditions, or submitted to abiotic stresses in the form of drought, heat and salinity or from plants infected with the Lily symptomless virus (LSV). The highest anti-herpetic effect was recorded in extracts from virus-infected plants (biotic stress), followed by extracts from plants submitted to heat stress. Similar antiviral effect was recorded for extracts from plants grown under regular conditions and under salinity. 80% methanolic fraction from heat-shock plants, rich in flavonoid was particularly efficient against HSV-1 infection. We suggest that stress conditions during plant growth increased leaf flavonoid content, inducing anti-herpetic efficiency. The fact that biotic and abiotic stress during plant growth increases anti-herpetic efficiency should be taken into consideration when growing plants for medicinal purposes.