Effects of enhanced UV-B radiation and epidermal UV screening in arctic and alpine plants

Abstract

Plants, as sessile organisms dependent on sunlight for their very existence, are often expected to be vulnerable to increasing UV-B radiation. During the last three decades, more than 800 articles have been published concerning UV-effects on plants (ISI database). Studies have been performed at all levels, from cellular investigations to large projects concerning the effects on entire ecosystems. Of the large number, however, less than 5 % of UVB response studies on plants have been conducted in the field, and even fewer with plants growing in their natural ecosystems (Caldwell et al. 1998). Only about ten studies have been published on the effects on plants from arctic and alpine areas. This chapter focuses on possible negative effects of increased UV-B radiation and protection against UV-B offered by absorbing pigments. The UV-absorbing compounds in higher plants are mainly located in the epidermis of leaves, where they screen damaging radiation before reaching the mesophyll cells. Experiments with mutants of higher plants have shown that the UV-B sensitivity of leaves and whole plants is strongly correlated with the concentrations of constitutive and UV-B induced screeningpigments in the epidermis (e.g. Lois and Buchanan 1994; Landry et al. 1995). UV-B screening compounds in higher plants are often phenolics, of which hydroxycinnamic acid esters (HCAs) and flavonoids are of particular importance. HCAs absorb mainly in the UV-B, while the flavonoids have a second major absorption band in the UV-A. An increased concentration of phenolic compounds in higher plants is a common response to UV-B, documented in numerous field and growth chamber studies, (for a review, see Searles et al. 2001).