Abstract
Lead is among the most contaminant metals in ecosystem and has different effects on anatomical and morphological characters of different plant species. Matricaria chamomilla is an important medicinal plant which contains 120 chemical compositions. In this research, the effects of lead on production of apigenin as a significant medicinal substance were studied. Furthermore, structural changes of M. chamomilla were studied in different stages of development by electron and optic microscopes. So the plants in first stage of development, were transplanted to hydroponic culture with five-treatment design of 0, 60, 120, 180, 240 µM Pb. The plants under treatment were harvested in first stage of development, as well as in shooting and flowering stages for measurement of Pb absorption. According to this study, morphological changes were not visually observed during the treatment process in different stages; nevertheless, reduction in total biomass was detected in different stages compared to control plants. The results of SEM study of leaf indicated structural changes in stomata and epicuticular waxes in different stages. Also in anatomical studies we noticed several changes in cross section of leaf, stem and root. The obtained results indicated that in different stages, Pb accumulation in roots and shoots has increased under Pb stress during various stage of development. Moreover, Pb stress has no effect on apigenin content. Therefore, M. chamomilla is an excluder species which is tolerant to Pb stress.
Highlights
Increase in heavy metal content of the environment has become one of the serious ecological problems, which threatens ecosystems and human health [15, 11]
We studied response of M. chamomilla to Pb toxicity in different stages of development in order to determine the growth stage at which the highest content of Pb can be restored from environment
Ninety-day-old Matricaria chamomilla L. plants were transplanted to 1⁄2 slightly modified Hoagland solution routinely with continual aeration used in our laboratory [25]
Summary
Increase in heavy metal content of the environment has become one of the serious ecological problems, which threatens ecosystems and human health [15, 11]. Pb pollution of the environment has resulted from mining and smelting activities, Pb-containing paints, gasoline and municipal sewage sludge enriched in Pb [23]. Such a pollution induces negative effects on plant anatomical, morphological and physiological characters such as a significant reduction in biomass production, growth inhibition, induction of leaf chlorosis, reduction in photosynthesis, repression on seed germination, inhibition and activation of enzymatic activities, and a decrease or increase in secondary metabolites content [24,18]. Because of the mentioned adverse effects, techniques have been developed in order to remediate contaminated soils, including solidification, soil washing and permeable barriers These technologies are expensive and cause further disturbance to the environment. Bio-concentration factor (BCF): the ratio of metal concentration in plant to soil, and translocation factor (TF): the ratio of metal concentration in shoots to roots, are greater than 1.0 in this type
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