Responses to ultraviolet‐B radiation (280–315 nm) of pea (Pisum sativum) lines differing in leaf surface wax

Abstract

To test the hypothesis that leaf surface wax influences plant responses to UV‐B, 6 lines of cultivated pea (Pisum sativum L.), selected as having more or less wax, were grown at 0 or 6.5 kJ m‐2 day‐1 plant‐weighted UV‐B against a background of 850–950 μmol m‐2 s‐1 photosynthetically active radiation. In the 4 lines with least leaf surface wax the amount of wax on adaxial and abaxial leaf surfaces was increased following exposure to 6.5 kJ m‐2 day‐1 UV‐B, but UV‐B decreased surface wax in Scout, which had the greatest wax deposits. On the adaxial leaf surface, UV‐B radiation caused a shift in wax composition from alcohols to esters and hydrocarbons and the ratio of short to long chain length alkyl ester homologues was increased. There was no evidence of a shortening in carbon chain length of hydrocarbons, primary alcohols or fatty acids due to UV‐B and no significant correlation between wax amount and UV reflectance from leaves.UV‐B induced significant increases in UV‐absorbing compounds in the expanded leaves and buds of most lines. UV‐B reduced the growth of all lines. Foliage area (leaves plus stipules) declined by 5–30%, plant dry weight by 12–30%, and plant height by 24–38%. Reductions in growth occurred in the absence of any changes in chlorophyll fluorescence or photosynthetic rate. UV‐B also had no major effect on carbon allocation patterns. The effects of UV‐B on growth appeared to be due to changes in tissue extension and expansion. Indeed, many of the responses to UV‐B observed in this study of pea appear more consistent with indirect effects being expressed in developing tissues rather than through the direct action of UV‐B on mature tissues.There was no evidence that wax amount or biochemistry was associated with the sensitivity of the lines to UV‐B radiation. Furthermore, induction of pigments was not correlated with changes in growth. However, lines with the greatest constitutive amounts of pigments in unexpanded bud tissues were most tolerant of elevated UV‐B.