Internal Aluminum Block of Plant Inward K+ Channels

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Abstract
Aluminum (Al) inhibits inward K+ channels (Kin) 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 Kin inhibition, we performed patch clamp analyses on Kin in guard cells and on KAT1 channels expressed in Xenopus oocytes. Our results show that Al inhibits plant Kin by blocking the channels at the cytoplasmic side of the plasma membrane. In guard cells, single-channel recording revealed that Al inhibition of Kin 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 Kin.