RESPONSES TO ULTRAVIOLET-B RADIATION (280-315 NM) OF PEA (PISUM-SATIVUM) LINES DIFFERING IN LEAF SURFACE WAX

To test the hypothesis that leaf surface wax influences plant response s to UV-B, 6 lines of cultivated pea (Pisum sativum L.), selected as h aving 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) photo synthetically active radiation In the 4 lines with least leaf surface wax the amount of wax on adaxial and abaxial leaf surfaces was increas ed 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 ada xial leaf surface, UV-B radiation caused a shift in wax composition fr om alcohols to esters and hydrocarbons and the ratio of short to long chain length alkyl ester homologues was increased. There was no eviden ce of a shortening in carbon chain length of hydrocarbons, primary alc ohols or fatty acids due to UV-B and no significant correlation betwee n 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 (leave s plus stipules) declined by 5-30%, plant dry weight by 12-30%, and pl ant height by 24-38%. Reductions in growth occurred in the absence of any changes in chlorophyll fluorescence or photosynthetic rate. UV-B a lso 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 e xpansion. Indeed, many of the responses to UV-B observed in this study of pea appear more consistent with indirect effects being expressed i n 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. Fu rthermore, induction of pigments was not correlated with changes in gr owth. However, lines with the greatest constitutive amounts of pigment s in unexpanded bud tissues were most tolerant of elevated UV-B.