Regulation by external K+ in a maize inward shaker channel targets transport activity in the high concentration range.
An inward Shaker K(+) channel identified in Zea mays (maize), ZmK2.1, displays strong regulation by external K(+) when expressed in Xenopus laevis (African clawed frog) oocytes or COS cells. ZmK2.1 is specifically activated by K(+) with an apparent K(m) close to 15 mM independent of the membrane hyperpolarization level. In the absence of K(+), ZmK2.1 appears to enter a nonconducting state. Thus, whatever the membrane potential, this maize channel cannot mediate K(+) influx in the submillimolar concentration range, unlike its relatives in Arabidopsis thaliana. Its expression is restricted to the shoots, the strongest signal (RT-PCR) being associated with vascular/bundle sheath strands. Based on sequence and gene structure, the closest relatives of ZmK2.1 in Arabidopsis are K(+) Arabidopsis Transporter 1 (KAT1) (expressed in guard cells) and KAT2 (expressed in guard cells and leaf phloem). Patch-clamp analyses of guard cell protoplasts reveal a higher functional diversity of K(+) channels in maize than in Arabidopsis. Channels endowed with regulation by external K(+) similar to that of ZmK2.1 (channel activity regulated by external K(+) with a K(m) close to 15 mM, regulation independent of external Ca(2+)) constitute a major component of the maize guard cell inward K(+) channel population. The presence of such channels in maize might reflect physiological traits of C4 and/or monocotyledonous plants.
Su
Yan-Hua
YH
Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, Unité Mixte de Recherche 5004 Agro-M/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/Université Montpellier II, Montpellier, France.
North
Helen
H
Grignon
Claude
C
Thibaud
Jean-Baptiste
JB
Sentenac
Hervé
H
Véry
Anne-Aliénor
AA
D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000378:metabolism; D001483:Base Sequence; D027682:Cation Transport Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D045604:Extracellular Fluid / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism; D013045:Species Specificity; D003313:Zea mays / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; C108935:KT1 protein, Arabidopsis; D010940:Plant Proteins; D015221:Potassium Channels; C417563:ZMK2 protein, Zea mays; D011188:Potassium