Involvement of Potassium Transporter KUP9 in Potassium Distribution in Arabidopsis

Potassium is the most abundant cation in plant cells, crucial for many cellular processes such as turgor regulation and activation of enzymes. It was shown that cation channels and KT/HAK/KUP transporters participate in potassium uptake. Moreover KT/HAK/KUP transporters also participate in the regulation of cell size and in the auxin transport in roots.

In this study we examined the function of putative potassium transporter KUP9 (At4g19960). Kup9 mutant plants deprived of potassium showed obvious phenotype of short lateral roots while the main root was not affected. The cessation of lateral roots growth in kup9 mutants was correlated with thinning and shortening of their meristematic zone. These results suggest gradual termination of apical meristem activity in these roots.

Kup9 mutants contained significantly less potassium in roots then wild type plants after one-week potassium deprivation in hydroponic cultivation. In contrast, shoot potassium content was similar or even higher in kup9 plants.

Transcriptional and translational fuses of KUP9 showed that this transporter is expressed in vascular tissue. Taken together these results show that KUP9 probably participates in phloem recirculation of potassium. When this process is abolished by mutation of KUP9 potassium supply in the roots is insufficient and the cessation of growth occurs.