ACTION-POTENTIAL - A POSSIBLE SIGNAL IN ROOT TO SHOOT COMMUNICATION CAUSED BY WATER-DEFICIT AROUND ROOTS OF SUNFLOWER SEEDLING

Exposure of sunflower roots to polyethylene glycol (PEG-6000) induced osmotic: stress caused a rapid depolarization of surface electrical po tential at the shoot apex within 25 seconds. It was found that while t he leaf water potential and the osmotic potential in control seedlings showed no variation during the entire period of experimentation, the leaf wafer potential in polyethylene glycol treated seedlings started decreasing after 2 min of treatment without any marked change in the o smotic potential. Similarly, the stomatal resistance in control seedli ngs remained constant during the course of experimentation but the pol yethylene glycol treatment affected the stomatal resistance within 30 seconds and it continued to increase 3 min after the treatment. All th ese events occur in a time scale of seconds to minutes and in a sequen ce. It is concluded that the action potential acts as a signal in root -to-shoot communication under osmotic stress.