Alligatorweed is well known for its potassium (K+)-accumulatingcapabilities and its strong resistance to undesired growth conditions. Theresults of this study revealed properties of K+ accumulation andits contribution to drought stress in alligatorweed. In addition, weattempted to characterize the molecular mechanisms of K+accumulation in this plant. Alligatorweed plants showed a consistentincrease in biomass in response to external K+ concentrations,ranging from micromolar levels up to 50 mmol L−1; K+was also accumulated accordingly in the plants. The stem was the most K+-accumulating organ, accumulating up to 13% of the K+. Moreover, this K+ superaccumulation causedimproved resistance to drought stress. The apparent K+ uptake bythe roots showed a typical high-affinity property, and the Michaelisconstant increased at higher rates of plant K+ in the startingmaterials. Furthermore, three putative, K+-uptake transportercomplementary DNAs (cDNAs) were isolated from alligatorweed (ApKUP1, ApKUP2, and ApKUP3, respectively) usingdegenerated primers and rapid amplification of cDNA end techniques. Theexpression of ApKUP1 and ApKUP3 waspredominately localized to the leaves, whereas ApKUP2 wasexpressed throughout the entire plant. The expression of ApKUP1 and ApKUP3 was stimulated in thestems and roots when K+ was depleted from the external medium.Moreover, ApKUP3 expression was enhanced in the stem inresponse to abscisic acid treatment and drought stress. In conclusion, ourfindings provide further insight into the mechanisms of K+accumulation linked to K+ uptake in alligatorweed.