Plant cells must pass a K + threshold to re‐enter the cell cycle

Summary Potassium is an inevitable component of plant life, and potassium channels play a pivotal role in plant growth and development. The role of potassium and of K + channels in plant cell division and cell‐cycle progression, however, has not been determined so far. K + channel blocker studies with synchronized tobacco BY‐2 cells revealed that K + uptake is required for proper cell‐cycle progression during the transition from G 1 to S phase. Electrophysiological studies (patch‐clamp and voltage‐clamp techniques) showed a cell‐cycle dependency of K + channel activities and reduced driving force for K + uptake in dividing cells. Among the four Shaker‐like K + channel genes expressed in BY‐2 cells, NKT1 represents an inwardly rectifying K + channel that mediates K + uptake. NKT1 is transcriptionally induced during G 1 phase, while transcripts of the outward‐rectifier NTORK1 dominate S phase. Elongating BY‐2 cells appeared hyperpolarized (−101 ± 11 mV), and had elevated osmotic pressure and approximately twice the turgor pressure when compared with depolarized (−64 ± 8 mV) dividing cells. This indicates that cells have to gain a threshold K + level to re‐enter the cell cycle. Based on these findings, turgor regulation through modulation of K + channel density in plant cell division and cell‐cycle progression is discussed.