Abstract
Cytokinins are mainly transported from root to shoot through the xylem in the form of nucleoside cytokinins. Because there is currently little information on how nucleoside cytokinins enter into and exit from the xylem, it is important to identify and characterize the transporters of nucleoside cytokinins. As an attempt, we isolated and characterized potential ENTs (equilibrative nucleoside transporters, designated OsENT1 to 4) of rice. OsENT2 complemented a Saccharomyces cerevisiae mutant that is unable to synthesize adenine. Adenosine import into yeast cells expressing OsENT2 appeared not to require a transmembrane proton gradient because protonophore did not abolish adenosine transport. In competition experiments using various nucleoside cytokinins, the transport of 3H-adenosine by OsENT2 was preferentially inhibited by isopentenyladenine riboside and kinetin riboside. The details of the transport characters and gene expressions of OsENT2 will be presented.
