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Plant Physiol, September 2000, Vol. 124, pp. 223-230
Distinct Abscisic Acid Signaling Pathways for Modulation of
Guard Cell versus Mesophyll Cell Potassium Channels Revealed by
Expression Studies in Xenopus laevis
Oocytes1
Fedora
Sutton,*
Sunil S.
Paul,2
Xi-Qing
Wang, and
Sarah M.
Assmann
Plant Science Department, South Dakota State University, Box 2108, Brookings, South Dakota 57007 (F.S., S.S.P.); and Biology
Department, Pennsylvania State University, 208 Mueller Laboratory,
University Park, Pennsylvania 16802 (X.-Q.W., S.M.A.)
Regulation of guard cell ion transport by abscisic acid (ABA) and
in particular ABA inhibition of a guard cell inward K+
current (IKin) is well documented. However,
little is known concerning ABA effects on ion transport in other plant
cell types. Here we applied patch clamp techniques to mesophyll cell
protoplasts of fava bean (Vicia faba cv Long Pod) plants
and demonstrated ABA inhibition of an outward K+ current
(IKout). When mesophyll cell protoplast mRNA
(mesophyll mRNA) was expressed in Xenopus laevis
oocytes, IKout was generated that displayed
similar properties to IKout observed from
direct analysis of mesophyll cell protoplasts.
IKout expressed by mesophyll mRNA-injected
oocytes was inhibited by ABA, indicating that the ABA signal
transduction pathway observed in mesophyll cells was preserved in the
frog oocytes. Co-injection of oocytes with guard cell protoplast mRNA
and cRNA for KAT1, an inward K+ channel expressed in guard
cells, resulted in IKin that was similarly inhibited by ABA. However, oocytes co-injected with mesophyll mRNA and
KAT1 cRNA produced IKin that was not
inhibited by ABA. These results demonstrate that the mesophyll-encoded
signaling mechanism could not substitute for the guard cell pathway.
These findings indicate that mesophyll cells and guard cells use
distinct and different receptor types and/or signal transduction
pathways in ABA regulation of K+ channels.
1
This work was supported by the National Science
Foundation (grant nos. IBN-9421856 to F.S. and MCB 94-16039 to
S.M.A.) under the auspices of the National Aeronautics and Space
Administration/National Science Foundation Network for the Study of
Plant Sensory Systems. South Dakota State University experiment station
funds provided a portion of the graduate research assistantship (to
S.S.P.).
2
Present address: 4710 Sam Peck Road, #2138, Little Rock,
AR 72223.
*
Corresponding author; e-mail fedora_sutton{at}sdstate.edu; fax
605-688-4024.
© 2000 American Society of Plant Physiologists
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