TY - JOUR

T1 - A patch clamp study of Na+ transport in maize roots

AU - Roberts, Stephen K.

AU - Tester, Mark

PY - 1997/3

Y1 - 1997/3

N2 - The mechanisms mediating Na+ transport in higher plant roots were investigated by applying the patch clamp technique to protoplasts isolated from the cortex and stele of maize roots. In the cortex, permeation of Na+ through a time-dependent K+-selective inward rectifier was negligible. Instead, Na+ influx into maize roots probably occurs via an instantaneously-activating current. This current was partially inhibited by extracellular Ca2+, but was insensitive to extracellular TEA(+), Cs+ and TTX. In outside-out patches, a plasma membrane ion channel was found which mediated an inward Na+ current which, at least in part, underlies the whole-cell instantaneously-activating current, the unitary conductance of this channel was 15 pS in 102:121 mM Na+ (outside:cytosol). Channel gating was voltage-independent and distinct from that observed for the inwardly rectifying Kf-selective channel in the same cell type. Increasing extracellular Ca2+ from 0.1 to 1 mM reduced the open probability and unitary conductance of this channel. In 102 mM a(+):123 mM K+ (outside:cytosol) a P-Na: P-K of 2.1 was calculated. It is suggested that the plasma membrane Na+-permeable channel identified in the cortex of maize roots represents a pathway for low affinity Na+ uptake by intact maize roots. In the stele, permeation of Na+ through outwardly rectifying K+ channels was found to be negligible and the channels are thus unlikely to be involved in the transport of Na+ from the root symplasm.

AB - The mechanisms mediating Na+ transport in higher plant roots were investigated by applying the patch clamp technique to protoplasts isolated from the cortex and stele of maize roots. In the cortex, permeation of Na+ through a time-dependent K+-selective inward rectifier was negligible. Instead, Na+ influx into maize roots probably occurs via an instantaneously-activating current. This current was partially inhibited by extracellular Ca2+, but was insensitive to extracellular TEA(+), Cs+ and TTX. In outside-out patches, a plasma membrane ion channel was found which mediated an inward Na+ current which, at least in part, underlies the whole-cell instantaneously-activating current, the unitary conductance of this channel was 15 pS in 102:121 mM Na+ (outside:cytosol). Channel gating was voltage-independent and distinct from that observed for the inwardly rectifying Kf-selective channel in the same cell type. Increasing extracellular Ca2+ from 0.1 to 1 mM reduced the open probability and unitary conductance of this channel. In 102 mM a(+):123 mM K+ (outside:cytosol) a P-Na: P-K of 2.1 was calculated. It is suggested that the plasma membrane Na+-permeable channel identified in the cortex of maize roots represents a pathway for low affinity Na+ uptake by intact maize roots. In the stele, permeation of Na+ through outwardly rectifying K+ channels was found to be negligible and the channels are thus unlikely to be involved in the transport of Na+ from the root symplasm.

KW - maize root protoplasts

KW - Na+-permeable channel

KW - PLASMA-MEMBRANE

KW - SALT TOLERANCE

KW - ION CHANNELS

KW - CORN ROOTS

KW - CATION CHANNEL

KW - K+ CHANNELS

KW - RYE ROOTS

KW - SODIUM

KW - WHEAT

KW - CELLS

U2 - 10.1093/jxb/48.Special_Issue.431

DO - 10.1093/jxb/48.Special_Issue.431

M3 - Journal article

VL - 48

SP - 431

EP - 440

JO - Journal of Experimental Botany

JF - Journal of Experimental Botany

SN - 0022-0957

T2 - Annual Meeting of the Society-for-Experimental-Biology

Y2 - 24 March 1996 through 29 March 1996

ER -