Comparative study of catalase, pyruvate kinase, oxaloacetate decarboxylase, NAD-malate dehydrogenase activities in leaves and activity of H+ pumps ın roots of common bean plants exposed to salt stress

N. R. Guliyeva, E. S. Jafarov, H. G. Babayev
2020 Advanced Studies in Biology  
Activities of NAD-malate dehydrogenase (NAD-MDH, EC, oxaloacetate decarboxylase (OAD, EC, pyruvate kinase (PK, EC, catalase (CAT, EC involved in the metabolism of dicarbon acids such as malate and oxaloacetate (OA) in leaves of common bean (Phaseolus vulgaris L.) plants exposed to salt stress and activity of H+ pumps related to the mineral nutrition in the root cell system have been studied comparatively. It has been established that these enzymes acting
more » ... se enzymes acting in concert play an important role in maintaining the constant energy balance and creating stress tolerance of the organism by the regulation of the metabolic processes at various concentrations of NaCl. Introductıon About 1/15 of the Earth is known to be saline soils. Excessive absorption of salts in the soil causes osmotic shock in plant cells, resulting in disturbance of water balance, reduction in turgor pressure, stomatal closure, reduced intensity of photosynthesis, and destruction of the cell membrane system, which eventually leads to cell death [1] . High salt concentrations that increase the amounts of reactive oxygen species (ROS), such as singlet oxygen-1 O2, superoxide anion radical -O2 ·-, hydrogen peroxide H2O2, and hydroxyl radical -OH· cause oxidative stress [2] . ROS oxidizing the cell structure, proteins, and DNA can cause "damage" to a various degree [3] . It is known that only at high concentrations of H2O2, the enzyme catalase (CAT) catalyzes its decomposition to water and oxygen [4] . Ashraf and Harris observed a higher synthesis rate of low-molecular (25-33 kDa) weight, specific proteins, involved in the regulation of osmotic and turgor pressure, in salt-tolerant varieties exposed to salt stress [5] . Pyruvate is a final product of the anaerobic oxidation ensuring the energy balance of the organism. Being a universal substrate it plays an important role in a number of vital processes. Therefore, the study of biosynthesis and conversion reactions of pyruvate under salt stress is considered to be relevant. The enzymes OAD, NAD-MDH, NADP-MDH, NADP-ME, CA, PEPC, RBPC, etc. localized in the chloroplasts of C3 plants are directly or indirectly involved in pyruvate metabolism. NADP-MDH and MAD-ME are localized in the stroma, whereas PEPC, OAD, and CA in the membranes of chloroplasts and the similarity of the functions of these enzymes in many cases suggests that there is a strong biochemical environment around pyruvate. According to He and Hou, OA transported to chloroplasts causes not only malate reduction, but it is also decarboxylated resulting in the pyruvate synthesis and RBP-carboxylase (RBPC) reduces ribulose-1,5-bisphosphate (RBP) to triose phosphate at the expense of the final product of the reaction -CO2. Calvin cycle of photosynthetic CO2 assimilation starting with the involvement of RBPC as a catalyst provides the cell with intermediate metabolites and plastic substances [6] . The main part of pyruvate is synthesized in the conversion of PEP in the reaction catalyzed by pyruvate kinase (PK), which generates adenosine triphosphate (ATP). Ivanishev observed an increase in the activities of OAD and NAD-MDH enzymes in cotton plants exposed to drought [7] , which is in accordance with the intensifying metabolism of C4-dicarbon acids and biosynthesis of amino acids [8] . According to Hatch, an increase in the OA concentration up to 50-100 µM is one of the main reasons for high pyruvate concentrations in cell organoids [9] . Camp et al. revealed pyruvate dehydrogenase complex implementing pyruvate metabolism in C3 plant chloroplasts [10] . The main purpose of the presented paper was a comparative study of the effects of various NaCl concentrations on the activity of energetic enzymes of the synthesis and metabolism of pyruvate, playing a key role of a substrate in
doi:10.12988/asb.2020.91212 fatcat:xyzk27v3wzgwvarmi4w6ewepii