Alterations in Enzyme Activities in Leaves after Exposure of Plectranthus Sp. Plants to 900 mhz elec
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ELECTROMAGNETICFIELDSandELF
| Results and Discussion
The citric acid cycle (tricarboxylic acid cycle, Krebs cycle), is a series of enzyme-catalysed chemical reactions of central importance in all living cells that use oxygen as part of cellular respiration. In eukaryotes, the citric acid cycle occurs in the matrix of the mitochondrion. It is part of a metabolic pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy. Nicotinamide adenine nucleotide (NADH)-dependent malate dehydrogenase (MDH, EC 1.1.1.37) is an enzyme in the citric acid cycle that catalyzes the conversion of malate into oxaloacetate (utilizing the NAD/NADH cofactor system) and vice versa (reaction is reversible): (S)-malate + NAD + ↔ oxaloacetate + NADH + H + . The enzyme exists in all aerobics organisms. There are two MDH isozymes in eukaryotic cells: one which is located in the mitochondrial matrix and the other in the cytoplasm. In the plant’s chloroplast there is an additional NADP-dependent form of MDH (EC 1.1.1.82). Exposure of Plectranthus plants to 900 MHz for 1 hour EMF leads to decrease of MDH activity immediately after the end of treatment, as well as 2 hours later. MDH activity highly increases at 24 th hour after exposure (Fig. 1). Fig. 1. Alterations in NADH-MDH activity in Plectranthus leaves after 1 hour exposure to 900 MHz radiation. Isocitrate dehydrogenase (ICDH) is also an enzyme in the citric acid cycle. In eukaryotes, ICDH exists in two forms: an NAD + -linked enzyme (EC 1.1.1.41) found only in mitochondria and a NADP + -linked enzyme (EC 1.1.1.42) that is found in both mitochondria and cytoplasm. The ICDH step is one of the irreversible reactions in the citric acid cycle and therefore must be carefully regulated to avoid unnecessary depletion of isocitrate (and therefore an accumulation of alpha-ketoglutarate (α-KG)). In higher plants, α-KG provides the primary carbon skeleton for the assimilation of reduced inorganic nitrogen into amino acids through the glutamine synthetase/glutamate synthase cycle, and thus represents a key point in the linking of carbon and nitrogen metabolism. Plant NADP-ICDH is predominantly localized in the cytosol. Cytosolic NADP-ICDH is the major catalyst for the production of α - KG required for nitrogen assimilation. It is the predominant form in leaf extracts. NADPH is an essential electron donor in numerous biosynthetic and detoxification reactions. In animal, yeast and bacteria, the NADP-ICDH, which catalyzes the production of NADPH, is being recognized as an essential component of the antioxidative defence mechanisms. In plant cells, there is little information on the antioxidant properties of NADP- ICDH. The data obtained from Leterrier et al. indicate that in pea plants the cytosolic NADP-ICDH shows a differential response, at mRNA and activity level, depending on the type of abiotic stress and suggests that this dehydrogenase could have a protective antioxidant role against certain environmental stresses in plants (10). Exposure of Plectranthus plants to 900 MHz EMF for 1 hour decreases NADP-ICDH activity for one hour after the treatment (Fig. 2). Two hours later ICDH activity increases and remains increased up to 24 th hour after exposure tải về 0.92 Mb. Chia sẻ với bạn bè của bạn:
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