Effect of UV-B dose on biosynthesis of epicuticular waxes in blue spruce (Picea pungens Engelmann.) primary needles: Preliminary investigation

Blue spruce [Picea pungens Engelmann.] seedlings were reared from seed for 8 weeks under one of seven UV-B doses ranging from 0.0 to 9.2 kJ m(-2) d(-1 ). Emerging primary needles were chopped and incubated 48 h (22 degrees C; 750 mu mol m(-2) s(-1) PAR) with [1-C-14] CH3COONa. Radioactivity incorpora ted into epicuticular waxes was measured using radio thin-layer chromatogra phy. Biosynthesis of nonacosan-10-ol, the dominant constituent, was affecte d by the UV-B dose. The results suggest that, if no other factors are limit ing, the optimum UV-B dose for wax biosynthesis in emerging primary needles of blue spruce is 6-7 kJ m(-2) d(-1). This dose is below that routinely me asured in some northern temperate forests and well within the range of pred icted values under stratospheric ozone depletion scenarios. UV-B dose level s above this threshold may cause changes to the wax composition that may pr edispose the tree to damage from other environmental stresses.