Тяжелые металлы в окружающей среде
HEAVY METAL TOLERANCE IN PLANTS - NEW AND EMERGING
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- Heavy metals – effects on plant functions and development
| HEAVY METAL TOLERANCE IN PLANTS - NEW AND EMERGING
BIOTECHNOLOGICAL SOLUTIONS Bojin Bojinov Head, Department of Genetics and Plant breeding, Agricultural University of Plovdiv Keywords: heavy metals, phytotoxicity, biotechnology, hyperaccumulation. The term ―heavy metals‖ in plant science refers to a series of metals and metalloids that can be toxic even at very low concentrations. Most of them (i.e. As, Cd, Hg, Pb or Se) do not perform any known physiological function in plants. Others (such as Co, Cu, Fe, Mn, Mo, Ni and Zn) are included in different plant metabolic pathways and thus are required for normal growth and devel- opment. While their presence may be needed to the plants, an excess of these elements can easily lead to poisoning as their concentration rises above optimal. These high concentrations negatively impact the organisms and such an impact is termed ―heavy metal phytotoxicity‖. It results in major changes in the functioning of the roots and leaves that affect other developmental processes such as flowering, embryogenesis and seed formation. Heavy metals – effects on plant functions and development Reduced growth is one of the most common physiological consequences of heavy metal ex- posure in plants. Metal ion-induced changes in the structural and physiological integrity of leaves reduce the rates of photosynthesis and respiration, which has deleterious effects on energy provision and the efficiency of other metabolic processes. Transpiration and transport processes between var- ious organs are also affected. Plant roots are directly exposed to the heavy metal content of contaminated soils and are the first to be affected by that exposure. Furthermore, they have rather simple and predictable structural organization and developmental zonation, which makes them ideal model systems for studying plant adaptations to abiotic stresses. Studies show that higher concentrations of heavy metals may result in alterations of numerous physiological processes due to: (1) inactivating enzymes, (2) blocking functional groups of metabolically important molecules, (3) displacing or substituting for other essential elements and (4) disrupting membrane integrity. A rather common consequence of heavy metals‘ presence is the interference with electron transport inside cells, especially that of chloroplast membranes. It results in an enhanced production of reactive oxygen species (ROS). While ROS are important signaling molecules on the one hand, they can have adverse effects on cell membranes when present in large quantities. This is likely to trigger specific defense responses in certain places – i.e., along the root axis, they can trigger cell wall cross-linking and lignification. ROS overproduction following exposure to high Cd concentra- tions leads to lipid peroxidation and subsequent cell death. Other effects may include biological macromolecule deterioration, membrane dismantling, ion leakage, DNA-strand cleavage, etc. Alto- gether these result in a plant state generally described as ―oxidative stress‖. It is interesting to notice that there are plants that survive, grow and reproduce on natural metalliferous soils as well as on sites polluted with heavy metals as a result of anthropogenic activi- ties. The majority of species that tolerate heavy metal concentrations that are highly toxic to the other plants behave as ―excluders‖, relying on tolerance and even hypertolerance strategies helpful 58 59 strong deficit balance of Cu, Mn and Zn - important trace elements, slightly negative balance of Cr and Ni, weakly positive balance of Cd and Pb. UDC 502:574:581 жүктеу/скачать 6.49 Mb. Достарыңызбен бөлісу:
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