Light dependent gibberellin responses in hypocotyls of Lactuca sativa L.

Abstract

GA 3 promotes lettuce hypocotyl extension by overcoming inhibition by light. Both phytochrome and a blue light receptor are involved in the photocontrol of the lettuce hypocotyl. In etiolated hypocotyls far red inhibits growth through a phytochrome high irradiance reaction (HIR). This is lost during de-etiolation and is possibly replaced by a fluence-dependent inhibition by red or yellow light also mediated by phytochrome. Blue light is inhibitory at all times and gibberellic acid (GA 3) antagonises all types of light inhibition. The optimum concentration for applied GA 3 shifts from 10 −4 M to 10 −5 M during de-etiolation and this appears to be a phytochrome effect. Blue light increases the sensitivity of the hypocotyls to applied GA 3 in both etiolated and de-etiolated seedlings.