GENETIC CHARACTERIZATION OF INDIAN MUSTARD (Brassica juncea) GENOTYPES TOLERANT TO HEAVY METALS

Abstract

In the present research work, ethyl methanesulfonate (EMS) agent was applied to select highly tolerant Indian mustard (Brassica juncea) plants to some heavy metals (zinc, cadmium, nickel, and molybdenum). Four hyper-accumulator lines were selected, that proved to be more tolerant to the corresponding heavy metal when compared to the wild-type control, for genetic analysis in an attempt to elucidate the genetic bases of heavy metal tolerance in higher plants. Total soluble protein electrophoretic profiles indicated that metallothioneins (5-8 kDa) were expressed in Cd, Mo, Ni, and Zn hyperaccumulator lines when compared with their corresponding wild-type plants. Peroxidase and super oxide dismutase isozyme patterns were not conclusive. The expression of glutathione synthetase (GSH) gene(s) was monitored in the four genotypes lines and the wild-type control, using RT-PCR technologies. Increases ranging between 5 to 2 folds were encountered in the genotypes lines relative to the controls. According to the present findings, it seems that B. juncea hyperaccumulator genotypes have evolved a number of mechanisms to cope with heavy metal stress such as the expression of several metallothioneins and the over expression of GSH gene(s). However, the results of oxygen radical scavengers were not conclusive, and need further justifications.