  This work is a study of the inter-relationship between parameters that
principally affect metal up-take in the plant. The relationships between the
concentration of metal in the growth medium, Cs, the concentration of metal
absorbed by the plant, Cp, and the total biomass achieved, M, all of which are
factors relevant to the efficiency of phytoremediation of the plant, have been
investigated via the macro-physiological response of Brassica juncea seedlings
to Ni(II) stress. The factorial growth experiments treated the Ni(II)
concentration in the agar gel and the diurnal light quanta (DLQ) as
independently variable parameters. Observations included the evidence of light
enhancement of Ni toxicity at the root as well as at the whole plant level, the
shoot mass index as a possible indicator of shoot metal sequestration in B.
juncea, the logarithmic variation of Cp with Cs and the power-law dependence of
M on Cp. The sum total of these observations indicate that for the metal
accumulator B. juncea with regard to its capacity to accumulate Ni, the overall
metabolic nature of the plant is important; neither rapid biomass increase nor
a high metal concentration capability favor the removal of high metal mass from
the medium, but rather the plant with the moderate photosynthetically driven
biomass growth and moderate metal concentrations demonstrated the ability to
remove the maximum mass of metal from the medium. The implications of these
observations in the context of the perceived need in phytoremediation
engineering to maximize Cp and M simultaneously in the same plant, are
discussed.
