Journal of Experimental Botany, Vol. 54, No. 383, pp. 657-661,
February 1, 2003
© 2003 Oxford University Press
Potassium activities in cell compartments of salt-grown barley leaves
Received 6 June 2002; Accepted 3 October 2002
1 Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK
2 Agriculture and Environment Division, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK
3 Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, Bristol BS18 9AF, UK
4 To whom correspondence should be addressed. Fax: +44 (0)1223 333953. E-mail: RL225{at}cam.ac.uk
Triple-barrelled microelectrodes measuring K+ activity (aK), pH and membrane potential were used to make quantitative measurements of vacuolar and cytosolic aK in epidermal and mesophyll cells of barley plants grown in nutrient solution with 0 or 200 mM added NaCl. Measurements of aK were assigned to the cytosol or vacuole based on the pH measured. In epidermal cells, the salt treatment decreased aK in the vacuole from 224 to 47 mM and in the cytosol from 68 to 15 mM. In contrast, the equivalent changes in the mesophyll were from 235 to 150 mM (vacuole) and 79 to 64 mM (cytosol). Thus mechanisms exist to ameliorate the effects of salt on aK in compartments of mesophyll cells, presumably to minimize any deleterious consequences for photosynthesis. Thermodynamic calculations showed that K+ is actively transported into the vacuole of both epidermal and mesophyll cells of salinized and non- salinized plants. Comparison of the values of aK in K+-replete, non-salinized leaf cells with those previously measured in root cells of plants grown under comparable conditions indicates that cytosolic aK is similar in cells of both organs, but vacuolar aK in leaf cells is approximately twice that in roots. This suggests differences in the regulation of vacuolar aK, but not cytosolic aK, in leaf and root cells.
Key words: Barley, cytosol, potassium, salinity, vacuole.
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