A gene responsible for transporting the essential mineral nutrient potassium into plants has been identified by researchers at UC San Diego, UC Davis and Northwestern University. Their study bringsscientists a big step closer to understanding why some plants can grow in seawater, while others -- including most crop plants -- cannot. The researchers found that this particular transport system prefers taking potassium into the plant, but when sodium concentrations in the soil become very high the same life-giving transport mechanism will take sodium into the plant and kill it. The challenge for scientists is to figure out how to encourage plants to continue selecting potassium from the soil even in saltier conditions, says UC Davis botany professor William Lucas, one of the authors of the study published last month in the journal Science. Cloned from the leafy Arabidopsis thaliana plant, the KAT1 gene had been identified earlier this year as a possible potassium transporter. Testing the KAT1 gene in a different genetic system (a maturing frog egg) in the lab of UC San Diego assistant biology professor Julian Schroeder, researchers determined the gene's membrane transport function as an inward potassium channel (that is, a one-way route directing potassium into the plant cells). This gene's transport system acts like a doorman in an exclusive club, denying entry to most substances except for potassium and limited amounts of other ions, such as sodium, through the plant cell membrane.