Impacts of different soil zinc levels on growth and Zn accumulation in Ethiopian mustard (Brassica carinata) and Indian mustard (Brassica juncea) with emphasis on phytoremediation

The current development of industry and technology has been associated with the entry of environmental pollutants and particularly heavy metals into the soil, and accordingly it raised the safety concerns of the international community. Zinc is an essential heavy metal in plants which involves in many biological functions, but at high concentrations inhibits plants growth and development and may endanger the health of human and other organisms in case of plant consumption. It can play catalytic, cocatalytic (coactive), or structural roles in a large number of enzymes and is involved in the biosynthesis and catabolism of proteins, nucleic acids, carbohydrates and lipids. In this research the tolerance of Ethiopian and Indian mustards grown in soils contaminated with different Zn concentrations and the accumulation of this element in these plants were investigated to assess their phytoremediation potentials.
Plants were grown in greenhouse in soils contaminated with 500 and 1000 mg kg-1 of zinc. The experiment was carried out in a factorial completely randomized design. Factor one was Zn and factor two was plant species.They were harvested after 7 weeks of growth at the beginning of the reproductive phase and assayed for growth characteristics and Zn concentration and photosynthetic pigments content.
The results showed that Zn treatments had no significant effect on growth parameters of both species except decrease in root length of Ethiopian mustard under 1000 mg kg-1 Zn. Both specices indicated great stress tolerance index to zinc. As soil zinc contamination increased, the concentration of Zn increased significantly in roots and shoots of both Ethiopian and Indian mustards. The greatest bioconcentration factor in root and shoot and translocation factor in both plants were observed under 500 mg kg-1 Zn treatment. In Ethiopian mustard, 1000 mg kg-1 Zn treatment reduced chlorophyll a and the ratio of total chlorophyll to carotenoids, however, Zn treatments did not affect significantly the photosynthetic pigments in Indian mustard.
Both species are able to tolerate and accumulate Zn under different Zn contamination levels, thus in both species increased soil Zn contamination led to increased stress tolerance index. The highest bioconcentration and translocation factors in both plants occurred under 500 mg kg-1 Zn. Under 1000 mg kg-1 Zn, Indian mustard accumulated 0.05 % Zn in shoots which was greater 1.5 fold than Ethiopian mustard. Accordingly, Inadian mustard has greater competence for phytoremediation of Zn contaminated soils compared to Ethiopian mustard.