A REDUCED XYLEM PRESSURE ALTERED THE ELECTRIC AND GROWTH-RESPONSES INCUCUMBER HYPOCOTYLS

This study measured the electric and growth responses in excised cucum ber hypocotyls and compared them with those in intact seedlings, Root excision (first severing cut) eliminated most of the positive xylem pr essure (P-X) in the hypocotyl, caused a rapid, transient drop in the h ypocotyl growth rate (GR) and some small, local depolarization near th e cut site, Although accompanied by a smaller decrease in P-X, a secon d, severing cut in the basal hypocotyl caused a decrease in GR which w as no longer transient and a depolarization which was increased in bot h size and extent, These changes were not wound effects because they c ould be simulated by root incubation in mannitol, The reduced GR recov ery occurred also in the absence of electric changes after a second in crease in the mannitol concentration incubating the root of intact see dlings, Increased electric sensitivity and altered growth response the refore appear to be two independent examples of physiological changes resulting from a lowered P-X.