Relative morpho-physiological responses of millets and oats against lead toxicity

Abstract Lead (Pb) toxicity due to accumulation in pearl millet (Pennisetum glaucum (L.) R. Br.), finger millet (Eleusine coracana (L.) Gaertn.) and oat (Avena sativa L.) was investigated. Seeds were grown on MS medium supplemented with 0–40 mg/l Pb and their response was noted after 15 days of germination. Accumulation of Pb in all the 3 species increased with increasing Pb, and maximum accumulation (91.3 ± 1.8 mg/l) was noted in roots of finger millet at 40 mg/l Pb. Toxicity effect of Pb accumulation was determined in terms of seed germination, seedling growth, chlorophyll and proline content, and antioxidative activity. Maximum decline in seed germination (78.5 %) was noted in oats. Inhibition of shoot (∼75–78.3 %) and root (∼97–98 %) elongation was maximum in pearl millet and oat, while reduction in biomass accumulation was maximum in shoot (67 %) and root (∼74 %) in oat. Chlorophyll content decreased significantly and was minimum (1.01 ± 0.03 mg/g FW) in pearl millet at 40 mg/l Pb. Higher SOD and GPX activities were noted in all the plantlets, while CAT activity decreased with increasing Pb levels in the medium. At the highest Pb concentration, proline accumulation (13.1 ± 0.17 μM/g FW), MDA content (22.1 ± 0.20 μmol/g FW), SOD activity (58.73 ± 0.69 U/mg protein) and GPX activity (1.5 ± 0.01 U/g FW) were maximum in oat roots, while CAT activity (75.03 ± 2.37 mg H2O2 destroyed/5 min/g FW) was maximum in shoots of finger millet. Finger millet was more tolerant to Pb toxicity and showed significant accumulation potential in both above and below ground parts. This study provides an overview of toxicity and tolerance mechanism of millets and oats against Pb stress. The study helps in understanding the mechanism of detoxification of lead employed by the plants and to select tolerant plant variety which could be used to bioremediate the lead contaminated soils.