Influx and accumulation of Cs+ by the akt1 mutant of Arabidopsis thaliana (L.) Heynh. lacking a dominant K+ transport system

An extensive literature reports that Cs+, an environmental contaminant, ent ers plant cells through K+ transport systems. Several recently identified p lant K+ transport systems are permeable to Cs+. Permeation models indicate that most Cst uptake into plant roots under typical soil ionic conditions w ill be mediated by voltage-insensitive cation (VIC) channels in the plasma membrane and not by the inward rectifying K+ (KIR) channels implicated in p lant K nutrition. Cation fluxes through KIR channels are blocked by Cs+. Th is paper tests directly the hypothesis that the dominant KIR channel in pla nt roots (AKT1) does not contribute significantly to Cs+ uptake by comparin g Csf uptake into wild-type and the akt1 knockout mutant of Arabidopsis tha liana (L.) Heynh. Wild-type and akt1 plants were grown to comparable size a nd Kt content on agar containing 10 mM Kt. Both Cs+ influx to roots of inta ct plants and Cs+ accumulation in roots and shoots were identical in wild-t ype and akt1 plants. These data indicate that AKT1 is unlikely to contribut e significantly to Cs+ uptake by wild-type Arabidopsis from 'single-salt' s olutions. The influx of Cs+ to roots of intact wild-type and akt1 plants wa s inhibited by 1 mM Ba2+, Ca2+ and La3+, but not by 10 muM Br-cAMP. This ph armacology resembles that of VIC channels and is consistent with the hypoth esis that VIC channels mediate most Cs+ influx under 'single-salt' conditio ns.