Differential Uptake of Transition Elements by Mesquite Obtained from Plants Grown in Impacted and Clean Sites1

In this research, the uptake of Cu, Mo, Zn, As(III) and Cr(VI) by mesquite (Prosopis spp.) roots and shoots from two different sources was studied. The first source was seeds collected from plants grown in mine tailings in Arizona, USA (Seeds A) and the other source was seeds from a commercial vendor (Seeds B). In addition, the effects of above mentioned elements on plant growth and nutrient uptake were also investigated. Plants were grown for seven days in hydroponic media containing different concentrations of Cu, Mo, Zn, As(III) and Cr(VI) (0, 1, 5 and 10 mg L). Plants grown from Seeds A grew faster and taller at a concentration of 1 mg L of Cu, Mo, Zn, As(III) and Cr(VI) than at 0 mg L; whereas plants grown from Seeds B had opposite response. This suggests that the seeds obtained from the mesquite plants grown in mine tailings have more phytotoxic tolerance than that of the Seeds B. However, 90% of the plants from both seeds grown in 5 and 10 mg L of Cu, Mo, Zn, As(III) and Cr(VI) did not survive. This indicates that uptake of Cu, Mo, Zn, As(III) and Cr(VI) was influenced by its concentration in the growth medium. Uptake of Cu, Mo, Zn, As(III) and Cr(VI) by mesquite plants grown from Seeds A was 1.8 times greater than that of plants grown from Seeds B. At 1 mg L, the root and shoot elongation of plants grown from Seeds A was significantly greater than that of plants grown from Seeds B. Plants grown from Seeds A absorbed micro and macronutrients to a lesser extent as compared to those grown from Seeds B. Morphological (xylem and phloem) changes inside the plants grown from both seeds are currently being investigated by infrared (IR) imaging and scanning electron microscope (SEM) techniques. The significant amount of Cu, Mo, Zn, As(III) and Cr(VI) concentrated in the plants grown from Seeds A, as well as the more extensive elongation of roots and shoots than that of Seeds B, indicate that mesquite seeds obtained from plants grown in mine tailings could be better adapted seeds for plants that could be potential hyperaccumulator of Cu, Mo, Zn, As and Cr in the mine tailings. Additional