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Internal Aluminum Block of Plant Inward K⁺ Channels

Department of Plant and Microbial Biology, University of California, Berkeley, California 94720

¹ To whom correspondence should be addressed. E-mail sluan{at}nature.berkeley.edu; fax 510-642-4995

Aluminum (Al) inhibits inward K⁺ channels (K_in) in both root hair and guard cells, which accounts for at least part of the Al toxicity in plants. To understand the mechanism of Al-induced K_in inhibition, we performed patch clamp analyses on K_in in guard cells and on KAT1 channels expressed in Xenopus oocytes. Our results show that Al inhibits plant K_in by blocking the channels at the cytoplasmic side of the plasma membrane. In guard cells, single-channel recording revealed that Al inhibition of K_in occurred only upon internal exposure. Using both "giant patch" recording and single-channel analyses, we found that Al reduced KAT1 open probability and changed its activation kinetics through an internal membrane-delimited mechanism. We also provide evidence that a Ca²+ channel–like pathway that is sensitive to antagonists verapamil and La³+ mediates Al entry across the plasma membrane. We conclude that Al enters plant cells through a Ca²+ channel–like pathway and inhibits K⁺ uptake by internally blocking K_in.

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