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Plant Physiol, February 2002, Vol. 128, pp. 634-642
Diurnal and Circadian Regulation of Putative Potassium Channels
in a Leaf Moving Organ1
Menachem
Moshelion,2
Dirk
Becker,2
Katrin
Czempinski,
Bernd
Mueller-Roeber,
Bernard
Attali,
Rainer
Hedrich, and
Nava
Moran*
Department of Agricultural Biology, The Institute of Plant
Sciences, Faculty of Agricultural, Food and Environmental Quality
Sciences of the Hebrew University of Jerusalem, Rehovot 76100, Israel
(M.M., N.M.); Julius-von-Sachs-Insitute, Department of Botany I:
Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Platz 2, D97082 Wuerzburg, Germany (D.B., R.H.); University of Potsdam,
Department of Biochemistry, Karl-Liebknecht-Strasse 24-25, Haus 20, D-14476 Golm, Germany (K.C., B.M.-R.); and Department of Physiology
and Pharmacology, Sackler School of Medicine, Tel Aviv University, Tel
Aviv, Israel (B.A.)
In a search for potassium channels involved in light- and
clock-regulated leaf movements, we cloned four putative K channel genes
from the leaf-moving organs, pulvini, of the legume Samanea saman. The S. saman SPOCK1 is homologous to
KCO1, an Arabidopsis two-pore-domain K channel, the S.
saman SPORK1 is similar to SKOR and GORK, Arabidopsis
outward-rectifying Shaker-like K channels, and the
S. saman SPICK1 and SPICK2 are homologous to AKT2, a
weakly-inward-rectifying Shaker-like Arabidopsis K
channel. All four S. saman sequences possess the
universal K-channel-specific pore signature, TXXTXGYG, strongly
suggesting a role in transmembrane K+ transport. The four
S. saman genes had different expression patterns within
four leaf parts: `extensor' and `flexor' (the motor tissues), the
leaf blades (mainly mesophyll), and the vascular bundle (`rachis'). Based on northern blot analysis, their transcript level was correlated with the rhythmic leaf movements: (a) all four genes were regulated diurnally (Spick2, Spork1, and
Spock1 in extensor and flexor, Spick1 in
extensor and rachis); (b) Spork1 and
Spock1 rhythms were inverted upon the inversion of the
day-night cycle; and (c) in extensor and/or flexor, the expression of
Spork1, Spick1, and Spick2
was also under a circadian control. These findings parallel the
circadian rhythm shown to govern the resting membrane K+
permeability in extensor and flexor protoplasts and the susceptibility of this permeability to light stimulation (Kim et al., 1993). Thus,
Samanea pulvinar motor cells are the first described
system combining light and circadian regulation of K channels at the level of transcript and membrane transport.
1
This work was supported by The German-Israeli
Foundation for Scientific Research and Development, Jerusalem (research
grant no. G 193-207.02/94 to R.H. and N.M.).
2
Both authors contributed equally to this work.
*
Corresponding author; e-mail nava.moran{at}huji.ac.il; fax
972-8-946-7763.
© 2002 American Society of Plant Physiologists
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