DIFFERENTIAL GROWTH AND PHOTOSYNTHETIC RESPONSES AND PATTERN OF METAL ACCUMULATION IN SUNFLOWER (HELIANTHUS ANNUUS L.) CULTIVARS AT ELEVATED LEVELS OF LEAD AND MERCURY

Influence of lead and mercury levels (100 and 300 mg/Kg soil) on three sunflower cultivars (DK-4040, Hysun-33 and NK-278) was assessed by analyzing germination, various growth attributes (fresh and dry weights of root and shoot and plant height) and photosynthetic traits (leaf area, chlorophyll a, b and total) along with carotenoids. Bioaccumulation of metals in plant tissues were assessed by Atomic Absorption Spectroscopy (AAS). Both lead and mercury at a concentration of 100 mg/Kg of soil did not significantly influence the attributes studied. However, the most elevated level of metals (300 mg/Kg of soil) had caused a significant reduction of growth and pigments. Biomass production, leaf area, photosynthetic pigments and carotenoids content appeared to serve as potential indicators for metal tolerance. The results indicated distinct responses of the cultivars as well as differential effects of the tested metals. Among the cultivars, DK-4040 had consistently showed a better threshold for both metals at all levels as it excelled 11 traits for mercury and 8 for lead. Hysun-33 also showed some tolerance while, NK-278 appeared to be a sensitive cultivar for most of the attributes in the presence of lead and mercury. The elevated levels of lead appeared to be more injurious to plants as compared with mercury for Hysun-33 and NK-278. The greater toxicity of lead can be attributed to translocation of metal from the roots to the aerial tissues. The ability of DK-4040 for sustainable growth, integrity of chloroplast, existence of non enzymatic defense and restricted transfer of metal to above ground tissue seem to provide a compatible strategy for heavy metal tolerance. Based on the bioaccumulation of lead and mercury the cultivars can be placed among metal excluders.