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Plant Physiology 124 (1): 223-230

Copyright © 2000 by the American Society of Plant Physiologists.

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}; fax 605-688-4024.

© 2000 American Society of Plant Physiologists

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