Journal of Experimental Botany, Vol. 54, No. 390, pp. 2035-2043,
September 1, 2003
© 2003 Oxford University Press
Effects of salinity on cytosolic Na+ and K+ in root hairs of Arabidopsis thaliana: in vivo measurements using the fluorescent dyes SBFI and PBFI
Received 17 January 2003; Accepted 22 May 2003
Department of Horticulture, The Pennsylvania State University, 102 Tyson Bldg., University Park, PA 16802, USA
* To whom correspondence should be addressed. Fax: +1 814 863 6139. E-mail JPL4{at}psu.edu
Toxicity from sodium accumulation is an important aspect of salinity stress that has been well studied at the organ and tissue level. However, the effects of salinity on sodium accumulation in the cytosol, where much of the sodium toxicity is thought to occur, are poorly understood due to the difficulty of direct non-invasive measurements of ion activities in living cells. The Na+-sensing fluorescent probe sodium-binding benzofuran isophthalate (SBFI) and the K+-sensing fluorescent probe potassium-binding benzofuran isophthalate (PBFI) were used to quantify Na+ and K+ activity in living root hairs under salinity stress. The effects of exposure of Arabidopsis thaliana roots to 0, 30, 60 or 90 mM NaCl were observed during the 20 min immediately following salinization and also after 2 d of salinization, in plants supplied with 0.5, 2.0 or 5.0 mM Ca. SBFI and PBFI fluorescence was confined primarily to the cytoplasm, with very little signal from the vacuole. Sodium affected the quantification of K+ by PBFI, thus limiting the usefulness of this dye. Root hairs exposed to NaCl accumulated from 3060 mM Na+ within the first 5 min of salinization in 0.5 and 2.0 mM Ca2+, and up to 15 mM Na+ in the 5.0 mM Ca2+ treatment. Two days of salinization did not increase cytosolic Na+ concentrations beyond the values observed after 20 min of salinization. Cytosolic activities roughly corresponded with elemental analysis of combined dry matter fractions from whole plants. We conclude that SBFI and, to a lesser extent, PBFI are useful tools for quantifying the dynamics of ion activities in the cytosols of living plant cells.
Key words: Arabidopsis, cytosolic K, cytosolic Na, fluorescent dyes, root hairs, salinity.
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