Step by step: deciphering ion transport in the root xylem parenchyma.
Proton pumps produce electrical potential differences and differences in pH across the plasma membrane of cells which drive secondary ion transport through sym- and antiporters. We used the patch-clamp technique to characterize an H(+)-pump in the xylem parenchyma of barley roots. This cell type is of special interest with respect to xylem loading. Since it has been an ongoing debate whether xylem loading is a passive or an active process, the functional characterization of the H(+)-pump is of major interest in the context of previous work on ion channels through which passive salt efflux into the xylem vessels could occur. Cell-type specific features like its Ca(2+) dependence were determined, that are important to interpret its physiological role and eventually to model xylem loading. We conclude that the electrogenic pump in the xylem parenchyma does not participate directly in the transfer of KCl and KNO(3) to the xylem but, in combination with short-circuiting conductances, plays a crucial role in controlling xylem unloading and loading through modulation of the voltage difference across the plasma membrane. Here, our recent results on the H(+) pump are put in a larger context and open questions are highlighted.
Köhler
Barbara
B
Nature. 2002 Nov 21;420(6913):282-3
12447429
Plant Physiol. 2005 Mar;137(3):819-28
15734917
Plant J. 2002 Apr;30(2):133-42
12000450
Plant Physiol. 2004 Sep;136(1):2475-82
15375204
FEBS Lett. 2000 Jan 28;466(2-3):351-4
10682858
Plant Physiol. 1992 Aug;99(4):1509-14
16669066
Plant Mol Biol. 2003 Mar;51(5):773-87
12678562
Plant J. 2002 Mar;29(6):717-31
12148530
J Biol Chem. 2002 Nov 22;277(47):45338-46
12244056
Biochim Biophys Acta. 2000 May 1;1465(1-2):1-16
10748244
Plant Physiol. 2000 Jan;122(1):243-54
10631268
Plant Physiol. 1994 Jul;105(3):799-813
12232243
Plant J. 2002 Oct;32(2):185-94
12383084
Cell. 1998 Sep 4;94(5):647-55
9741629
Plant Physiol. 1997 Dec;115(4):1707-1719
12223889
J Exp Bot. 2000 Sep;51(350):1585-94
11006309
Proc Natl Acad Sci U S A. 2001 Jul 31;98(16):9443-7
11481499