Electrophysiological characterization of pathways for K(+) uptake into growing and non-growing leaf cells of barley.
Potassium is a major osmolyte used by plant cells. The accumulation rates of K(+) in cells may limit the rate of expansion. In the present study, we investigated the involvement of ion channels in K(+) uptake using patch clamp technique. Ion currents were quantified in protoplasts of the elongation and emerged blade zone of the developing leaf 3 of barley (Hordeum vulgare L.). A time-dependent inward-rectifying K(+)-selective current was observed almost exclusively in elongation zone protoplasts. The current showed characteristics typical of Shaker-type channels. Instantaneous inward current was highest in the epidermis of the emerged blade and selective for Na(+) over K(+). Selectivity disappeared, and currents decreased or remained the same, depending on tissue, in response to salt treatment. Net accumulation rates of K(+) in cells calculated from patch clamp current-voltage curves exceeded rates calculated from membrane potential and K(+) concentrations of cells measured in planta by factor 2.5-2.7 at physiological apoplastic K(+) concentrations (10-100 mm). It is concluded that under these conditions, K(+) accumulation in growing barley leaf cells is not limited by transport properties of cells. Under saline conditions, down-regulation of voltage-independent channels may reduce the capacity for growth-related K(+) accumulation.
Volkov
Vadim
V
Division of Biological Sciences, University of Paisley, Paisley PA1 2BE, UK.
Boscari
Alexandre
A
Clément
Mathilde
M
Miller
Anthony J
AJ
Amtmann
Anna
A
Fricke
Wieland
W
D001467:Hordeum / Q000254:growth & development* / Q000378:metabolism; D017136:Ion Transport; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism; D051637:Shaker Superfamily of Potassium Channels / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism
D051637:Shaker Superfamily of Potassium Channels; D012964:Sodium; D011188:Potassium