Combined Effects of Zinc and Copper on Seed Germination and Seedling Growth of Brassica Juncea L.

The aim of present study was to determine the combined effects of the elevated concentrations of Zn and Cu on seed germination and seedling growth of Brassica juncea L. Also, the TTC reduction ability (a measure of the activity of dehydrogenases) of the excised embryos and α-amylase activity in the seeds were monitored. Seed germination and seedling growth were differentially influenced by Zn and Cu, applied individually or in combinations. Higher Zn (= 500 μM) and Cu (= 50 μM) concentrations, applied individually, did not markedly influence the seed germination whereas the lower ones were promotory at 1 d; certain Zn-Cu mixtures also proved promotory. However, the promotion was completely abolished at 3 d. In contrast, the seedling growth was suppressed by Zn and Cu, applied individually or in combinations; magnitude of inhibition of root elongation was much stronger than that of shoot. Based on the analysis of root elongation data according to response additivity, the joint effects of Zn and Cu were found to be antagonistic except in a couple of combinations i.e. 250 μM Zn + 50 μM Cu and 500 μM Zn + 100 μM Cu. The TTC reduction ability of excised embryos was strongly promoted by most of the tested binary combinations of Zn and Cu whereas the same was only marginally promoted by certain Zn or Cu concentrations applied individually. The lower Zn and Cu concentrations were promotory for α-amylase activity when applied individually as well as in combination. In contrast, the higher ones suppressed the α-amylase activity individually but not in combination. The measured metabolic parameters seem to be among the early metabolic targets of heavy metals (HMs) in influencing the seed germination and subsequent growth.