Accumulation of a Metallothionein-like mRNA in Norway Spruce Under Environmental Stress

Differential screening of a Norway spruce (Picea abies L., Karst) cDNA library with probes from damaged and symptomless trees identified a cDNA clone of a 650 nt metallothionein-like (MTL) mRNA as damage-related. Northern blot analysis revealed an about six-fold increase of the MTL mRNA in damaged trees in 1 year and a two-fold increase in the consecutive year. In the N-terminal domain this MTL mRNA comprises typical CysXCys motifs of a subgroup of class II MTL proteins found in kiwi and a few other plant species. In the C-terminal domain, however, the Norway spruce MTL protein is different to the kiwi subgroup and also distinct from a novel Douglas fir metallothionein-related protein, respectively. Hence, the cDNA identified during this study may represent a new type of MTL protein in plants. The accumulation of this MTL mRNA in needles of trees growing in an area of high ozone, sulphur dioxide and nitrogen oxide input and showing clear symptoms of forest decline may be a senescence effect or may play a role in the metal-mediated regulation of the intracellular activated oxygen concentration.