A comparison of lead accumulation and growth factors of metallicolous and non- metallicolous populations of Marrubium cuneatum in hydroponic conditions

The present study was devoted to investigate the concentration of lead (Pb) in the tailings of Tang-e Douzan lead–zinc mine then determine the growth factors and the lead accumulation in metallicolous and non-metallicolous populations of Marrubium cuneatum in 2018 at the university of Isfahan. The both plant populations were transferred to hydroponic mediums and after proper vegetative growth, they were exposed different treatments of lead for 14 days. The results showed the highest Pb concentration in the tailings of mine (1968 mg/kg) was more than 72-fold the global average and by increasing lead concentration, the growth factors  decreased, but this reduction in growth was always greater in the non-metallicolous population, so that at the 200 mg/L treatment of lead, relative water content and shoot weight loss of the metallicolous population was 66.8 and 32.2%, respectively but they were 58.9 and 84.9% in non-metallicolous population in comparison with their control. With increasing the concentration of Pb in the medium, the accumulation of Pb in the roots and shoots of both populations are enhanced and lead accumulation was constantly more in the metallicolous population. The highest concentration levels of Pb were in the roots and shoots of the metallicolous population (15.2 and 0.9 mg per plant) which were 3.1- and 3.6-fold accumulation Pb in the non metallicolous population. The accumulation of lead in the roots was 15-folds more than the one in the shoots in both populations. The metallicolous population had an efficient antioxidant system which can grow with more accumulation of Pb and enhance the ratio of shoot to root, therefore, it can be used for phytoremediation.