Accumulation of a porin-like mRNA and a metallothionein-like mRNA in various clones of Norway spruce upon long-term treatment with ozone

In a long-term study six Norway spruce (Picea abies) clones from two different provenance regions were exposed to 150 mu g/m(3) and 300 mu g/m(3) ozone in open top chambers. Differential screening of subtractive cDNA libraries made from mRNA of ozone-treated trees identified several cDNA clones of ozone-responsive genes, two of which were studied in more detail. One cDNA clone corresponded to a porin-like mRNA, the other to a metallothionein-like mRNA. Under moderate ozone exposure the accumulation of these two mRNAs was already detectable before damage symptoms became visible. The spruce clones varied in the level of accumulation for the mRNAs. This is discussed under the aspect of ozone-induced early senescence rather than a defense reaction suppressing symptoms, because the two phenotypically most ozone-'tolerant' spruce clones showed the lowest levels of accumulation for both mRNAs.