Tolerance potential and physiological responses of Helianthus annuus L. exposed to varying doses of hexavalent chromium

The present investigation assesses the physiological and biochemical response of sunflower plants (helianthus annuus l.) to increased doses of hexavalent chromium (cr6++ ) at different growth periods (15,30 and 45 days) under in vivo condition. treatment with 500 mg cr6++/kg dry soil showed 80% inhibition in seed germination. the seedlings after 30 and 45 days of cr6++ treatment (100 mg/kg dry soil) showed negligible difference in their shoot length values,but it was significantly decreased using 200 mg cr6++/kg dry soil treatment. notable increase in root length was observed at 50 mg cr6++/kg soil treatment after 45 days of plant growth. plant biomass,chlorophyll and carotenoid contents of 45 days treated seedlings were significantly reduced at 200 mg cr6++/kg soil. the increase in total free amino acid accumulation was noted up to 30 days using different concentrations of cr6++ with maximum at 200 mg cr6++/kg dry soil but on 45 days it showed a decline value with some minor deviations using different concentrations of cr6++. the higher level of chromium accumulation in shoot in comparison to roots indicates the tolerance potential of h. annuus towards application of toxic doses of hexavalent chromium even through the survival capacity of the plants reduced with increasing cr6++ supply. this leads to evolved phytoremediation techniques using in situ application of the plant as a green tool.