An increase in the luteolin:apigenin ratio in Marchantia polymorpha on UV-B enhancement

The effects of varying the UV-B component in ambient light pn the liverwort, Marchantia polymorpha are reported. Plants grown under conditions of ambient light, ambient light lacking UV-B, and ambient light with a 25% enhancement of incident UV-B showed, with increasing levels of UV-B, a decrease in growth rate, a decrease in the production of gemmae cups and an increase in the proportion of dead thallus. Thallus surviving after three months of summer growth under these conditions showed no statistically significant increase in flavonoid levels with increasing UV-B levels. However, HPLC monitoring of individual flavonoids (all of which are apigenin and luteolin glucuronides) revealed a strong correlation between increasing UV-B levels and an increase in the ratio of luteolin to apigenin glycosides. It is considered unlikely that this change has significantly altered the UV-B screening effectiveness of the flavonoids. Rather, an improved level of antioxidant defence, or a more effective dissipation of absorbed UV energy, are proposed as possible UV-B protectant benefits to the plant. (C) 1998 Elsevier Science Ltd. All rights reserved.