Immediate phytochrome action in inducting α-galactosidase in lettuce seeds

Abstract

The light-induced breaking of dormancy of Grand Rapids lettuce seeds imbibed in darkness at 25°C is a classical phytochrome-controlled phenomenon1. Although it has been shown that irradiation of seeds 1–2 h after the start of imbibition produces the active form of phytochrome (Pfr) which acts rapidly after its formation2,3, the completion of germination (observed as radicle protrusion) is only evident several hours later. Clearly, then, radicle emergence is temporally removed from the rapid (and presumably primary) action of phytochrome. Very little is known about the processes set in motion by Pfr that lead to the completion of germination. Here we report that red light-induced stimulation of α-galactosidase (EC 3.2.1.22) activity occurs substantially before germination is completed, and show that the action of phytochrome in promoting an increase in the activity of this enzyme is very rapid.