Photosystem II and Hypoxic Quiescence in Alligatorweed

Abstract

Stem cuttings of alligatorweed lAlternanthera philo.xeroides (Mart.) Griseb.l were subjected to various light and chemical inhibitor treatments to obtain information about the physiological nature of the hypoxic quiescence induced by dark submergence. White or red light at 40 fiE m~^ s^' stimulated growth from submerged stem cuttings but far-red at 5 //E m~^ s ' did not. Photo system II inhibitors, such as 3-(3,4-dichlorophenyl) 1,1-dimethylurea (DCMU) at 1.4 X 10"' M or 2-chloro-4,6-bis(ethylamino)-striazine (simazine) at 10~' Af, completely inhibited the growth that normally occurs in a submerged state under continuous white light at 40 ftE s '. These concentrations of DCMU or simazine did not reduce nonphotosynthetic growth from underwater nodes of emersed stem cuttings partially exposed to air in the light for 1 week. Hydrogen peroxide at 50 mg/1 added every other day partially relieved the simazine-induced inhibition of growth from submerged, illuminated cuttings. These data indicated that sprouting and early growth of submerged, illuminated alligatorweed depended on the oxygen produced by photosystem II to support respiration and to overcome hypoxic quiescence.