Does the Ratio of Na+ and K+ Affect the Hydrolytic and Pumping Activity of the Plasma Membrane H+-Atpase from Maize (Zea Mays L.) Shoot?Journal: COMU Journal of Agriculture Faculty (Vol.1, No. 1)
Publication Date: 2013-08-07
Authors : Ali Sümer; Christian Zörb; Feng Yan; Sven Schubert;
Page : 43-50
Keywords : Zea mays; Na+/K+ ratio; plasma membrane; H+-ATPase; leaf growth;
Salinity limits plant growth and impairs agricultural productivity. In the first phase of salt stress, growth of plants is impaired predominantly by osmotic stress and only slightly by Na+ effects. The aim of our work was to investigate whether Na+ affects both hydrolytic and pumping activity of the plasma membrane H+ ATPase. Sodium salinity leads to a shift of the Na+/K+ ratio resulting in a displacement of K+ in the plant. It was shown that high cytoplasmatic Na+ concentrations and low K+ concentrations have an effect on the H+ ATPase activity of the plasma membrane. Reduced H+-ATPase activities caused a reduction of the acidification of the apoplast. This process limits the cell-wall extensibility and thus reduces growth after salt stress. For this reason, H+-ATPase activity, which is important for cell elongation was measured under the influence of different Na+/K+ ratios. Plasma membrane was isolated from two days old maize shoots using the aqueous polymer two-phase technique. ATPase activity was determined by measuring the release of Pi. The H+-pumping activity was revealed by absorbance quenching of acridine orange. Identical plant shoot material was used for ATPase extraction and effects of Na+ and K+ were tested in vitro. High concentration of 100 mM Na+ decreased the hydrolytic H+-ATPase activity to values of 80%, in comparison to high concentration of K+ (100 mM) without Na+. However, under comparable conditions the H+ pumping activity was decreased to 30%.
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