Expression of a metallothionein A1 gene of Pisum sativum in white poplar enhances tolerance and accumulation of zinc and copper.

Metallothioneins (MT) play an important role in heavy metal detoxification and homeostasis of intracellular metal ions in plant. In this study, two transgenic lines expressing MT type 2 gene (PsMT(A1)) from Pisum sativum, a regenerated non transformed line NT and clone AL22, selected as heavy metal tolerant, were characterized in presence of the heavy metals for the ability to accumulate zinc and copper and to activate antioxidative enzyme defences: superoxide dismutase, catalase, ascorbate peroxidase. The levels of expression of MT type 2 gene assessed by RT-qPCR confirmed the gene over-expression in transgenic lines and evidenced in NT and AL22 the up-regulation of gene transcription by zinc and copper. Transgenic poplar lines during heavy metal stress displayed increased ability to translocate and accumulate zinc and copper compared with NT and AL22. The antioxidant enzyme defence was differently activated in response to metals in the transgenic lines without a significant increase of ROS. These results suggested that PsMT(A1) could play a role in ROS scavenging leading to enhanced metal tolerance and increased zinc and copper sequestration in root and leaf.