Improved measurements of Na+ fluxes in plants using calixarene-based microelectrodes
Jayakannan, M and Babourina, O and Rangel, Z, Improved measurements of Na+ fluxes in plants using calixarene-based microelectrodes, Journal of Plant Physiology, 168, (10) pp. 1045-1051. ISSN 0176-1617 (2011) [Refereed Article]
Ion-selective microelectrodes are a powerful tool in studying adaptive responses of plant cells and tissues to various abiotic stresses. However, application of this technique in Na + flux measurements was limited due to poor selectivity for Na + ions of commercially available Na + cocktails. Often, these cocktails cannot discriminate between Na + and other interfering ions such as K + and Ca 2+, leading to inaccurate measurements of Na + concentration and, consequently, inaccurate Na + flux calculations. To overcome this problem, three Na +-selective cocktail mixtures were prepared using tetramethoxyethyl ester derivative of p-t-butyl calixarene. These cocktail mixtures were compared with commercially available ETH 227-based Na + cocktail for selectivity for Na + ions over other ions (particularly K + and Ca 2+). Among the three calixarene-based Na + cocktails tested, cocktail 2 [in % w/w: Na + ionophore (4-tert-butylcalixarene-tetra acetic acid tetraethyl ester) 3.5, the plasticizer (2-nitrophenyl octyl ether) 95.9 and lipophilic anion (potassium tetrakis (4-chlorophenyl) borate) 0.6] showed the best selectivity for Na + ions over K + and Ca 2+ ions and was highly stable over time (up to 10h). Na + flux measurements under a wide range of NaCl concentrations (25-150mM) using Na + cocktail 2 established a clear dose-response relationship between severity of salt stress and magnitude of Na + influx at the distal elongation and mature zones of Arabidopsis thaliana roots. Furthermore, Na + cocktail 2 was compared with commercially available ETH 227-based Na + cocktail by measuring Na + fluxes at the two Arabidopsis root zones in response to 100mM NaCl treatment. With calixarene-based Na + cocktail 2, a large decreasing Na + influx (0-15min) followed by small Na + influx (15-45min) was measured, whereas with ETH-based Na + cocktail Na + influx was short-lived (1-3min) and was followed by Na + efflux (3-45min) that might have been due to K + and Ca 2+ efflux measured together with Na + influx. In conclusion, Na ++ flux measurements in plants.
Arabidopsis, calixarene, ion fluxes, Na +-selective electrodes, salt stress