Expression of metallothionein type 2 and 3 genes in Prosopis glandulosa leaves treated with copper.

For a better understanding of the strategies that are used by Prosopis glandulosa in heavy metal tolerance, the present study evaluated the gene expression of three metallothioneins (MTs; PgMt2-1, PgMt2, and PgMt3) in plants exposed to sub-lethal concentrations of copper. The PgMt2-1, PgMt2, and PgMt3 sequences were homologous to the MT type 2 (isoform 1), Mt2, and Mt3 sequences of other plant species found in GenBank. A reverse transcriptase-polymerase chain reaction showed that treatment with 100 mM Cu induced a significant increase in PgMt2 and PgMt3 expression during the first 4 h of exposure compared to that of PgMt2-1. However, after 8 h of exposure, the expression levels of PgMt2 and PgMt3 were significantly lower than those of PgMt2-1. PgMt transcript levels only increased significantly during the first hour after exposure to copper, suggesting that PgMts could play a key role in the plant's detoxification mechanism. However, additional studies are required to confirm MTs as a mechanism of heavy metal tolerance and accumulation in this species.