ORIGINAL ARTICLE

Response of Heavy Metals Stress during Seed Germination and Early Seedling Growth in Oil Crop Black Sesame (Sesamum indicum L.)

During past few years, it has been globally experienced that uncontrolled urbanization and industrialization have contributed the accumulation of heavy metals in water and soil which causes physiological stress to the growing plants that finally leads to negative effects. Present study was undertaken to analyze the response of heavy metals (0.01%, 0.1%, and 1.0%) of HgCl₂ and equivalent concentrations of CoCl₂, NiCl₂,CdCl₂, ZnSO₄, and CuSO₄ (5mg/L, 10mg/L, 25mg/L, 50mg/L, and 100mg/L) during seed germination and early seedling growth in oil crop black sesame (Sesamum indicum L., cv. TMV3). Responses in terms of germination (partial and full) percentage mean were recorded after 3-days and 7-days of treatments respectively. Results reveal that even very low concentration (0.01%) of HgCl₂ treatment was seen to be significantly inhibitory leading to full seed germination (60±1.0%) after 7-days of treatments in comparison to control experiment (100±0.5%). Moreover, further higher concentration (0.1%) of HgCl₂ was proved to be completely lethal. Among solutions of chloride metals (Co, Ni, and Cd), NiCl₂ (25mg/L) was found to be the most toxic heavy metal and the rate of germination was recorded as (10±1.0%) followed by CdCl₂ (40±1.0%) and CoCl₂ (50±1.0%) after 7-days of treatments. Further, among sulfate solutions of Zn and Cu- heavy metals, CuSO₄ (100mg/L) proves to be strongly inhibitory (0±0.0%) for sesame seed germination in comparison to ZnSO₄ (30±0.5%). Significantly, very low concentration (0.01%) of HgCl₂ was also emerged as significantly toxic for seedling growth, hence, root-shoot length ratio (0.38±0.14cm/0.44±0.16cm) of seedlings were recorded after 10-days of treatments in comparison to control seedling (2.11±1.04cm/3.77±0.19cm). However, among chloride solutions of cobalt, nickel, and cadmium, NiCl₂ solution even with (10mg/L) was proved to be strongly inhibitory during early seedling growth and thus, root-shoot length ratio (0.03±0.02cm/0.33±0.22cm) was recorded. Moreover, further higher concentrations (25mg/L and above) of NiCl₂ treatments were proved to be strongly lethal and suppressed significantly both seed germination and seedling growth. Additionally, CoCl₂ and CdCl₂ treatments were also exhibited similar inhibitory responses in terms of inhibitions in root formation at high concentration (25mg/L). Furthermore, during sulfate solutions of Zn and Cu-treatments, CuSO₄ solution (100mg/L) was found to be strongly inhibitory even for seed germination while in contrast ZnSO₄ (100mg/L) solution was failed to suppress seed germination completely and seedling length (0.1±0.11cm/0.11±0.6cm) was recorded. Hence, present study reveals that among various heavy metals employed, Hg was found to be the strongest inhibitor for sesame seed germination and during early seedling growth followed by Ni, Cd, and Co while Zn was proved as very weak inhibitor in comparison to Cu heavy metal.