TOWARDS AN UNDERSTANDING OF THE MOLECULAR-BASIS OF PLANTS K- CHARACTERIZATION OF CLONED K+ TRANSPORT CDNAS( TRANSPORT )

Recently, two K+-transport cDNAs, KAT1 and AKT1, were cloned in Arabid opsis thaliana. These cDNAs had structural similarities to K+ channel genes in animals, and also conferred the ability for growth on micromo lar levels of K+ when expressed in K+ transport-defective yeast mutant s. In this study, we examined the possibility that KAT1 encodes the hi gh-affinity K+ transport system that has been previously characterized in plant roots, by studying the concentration-dependent kinetics of K + transport for KAT1 expressed in Xenopus oocytes and Saccharomyces ce revisiae. In both organisms, the K+ transport system encoded by KAT1 y ielded Michaelis-Menten kinetics with a high K-m for K+ (35 mM in oocy tes, 0.6 mM in yeast cells). Furthermore, Northern analysis indicated that KAT1 is expressed primarily in the Arabidopsis shoot. These resul ts strongly suggest that the system encoded by KAT1 is not a root high -affinity K+ transporter.