Light dependent promotion and inhibition of adventitious root formation by gibberellic acid.

Cuttings from plants of Pisum sativum L. cv. "Alaska" which had been grown at an irradiance of 16 W m(-2) formed a higher number of roots than cuttings from plants grown at 38 W m(-2). (Irradiance during the rooting period always 16 W m(-2).) High concentrations of gibberellic acid (GA3) inhibited rooting in cuttings from both types of stock plants. Low concentrations (10(-9)-10(-6) M) of GA3 were without effect in cuttings from plants irradiated with 38 W m(-2), but promoted rooting when the stock plants had been grown at 16 W m(-2).