EXPRESSION OF A CS-RESISTANT GUARD-CELL K+ CHANNEL CONFERS CS+-RESISTANT, LIGHT-INDUCED STOMATAL OPENING IN TRANSGENIC ARABIDOPSIS()

Inward-rectifying K+ (K-in(+)) channels in the guard cell plasma membr ane have been suggested to function as a major pathway for K+ influx i nto guard cells during stomatal opening. When K-in(+) channels were bl ocked with external Cs+ in wild-type Arabidopsis guard cells, light-in duced stomatal opening was reduced, Transgenic Arabidopsis plants were generated that expressed a mutant of the guard cell K-in(+) channel, KAT1, which shows enhanced resistance to the Cs+ block. Stomata in the se transgenic lines opened in the presence of external Cs+. Patch-clam p experiments with transgenic guard cells showed that inward K-in(+) c urrents were blocked less by Cs+ than were K+ currents in controls. Th ese data provide direct evidence that KAT1 functions as a plasma membr ane K+ channel in vivo and that K-in(+) channels constitute an importa nt mechanism for light-induced stomatal opening, In addition, biophysi cal properties of K-in(+) channels in guard cells indicate that compon ents in addition to KAT1 may contribute to the formation of K-in(+) ch annels in vivo.