METALLOTHIONEIN-1 AND METALLOTHIONEIN-2 HAVE DISTINCT BUT OVERLAPPINGEXPRESSION PATTERNS IN ARABIDOPSIS

The spatial and temporal expression patterns of metallothionein (MT) i soforms MT1a and MT2a were investigated in vegetative and reproductive tissues of untreated and copper-treated Arabidopsis by in situ hybrid ization and by northern blotting. In control plants, MT1a mRNA was loc alized in leaf trichomes and in the vascular tissue in leaves, roots, flowers, and germinating embryos. In copper-treated plants, MT1a expre ssion was also observed in the lear mesophyll and in vascular tissue o f developing siliques and seeds. In contrast, MT2a was expressed prima rily in the trichomes of both untreated and copper-treated plants. In copper-treated plants, MT2a mRNA was also expressed in siliques. North ern-hybridization studies performed on developing seedlings and leaves showed temporal variations of MT1a gene expression but not of MT2a ex pression. The possible implications of these findings for the cellular roles of MTs in plants are discussed.