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 mu mol 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.