The Effect of Auxin on Suckering in Black Locust

Abstract

Experiments were conducted on black locust (Robinia pseudoacacia L.) to determine the effect of auxin distribution and degradation on the formation of root suckers. Stump sprouting and root suckering occurred when black locust seedlings were decapitated, and the presence of stump sprouts prevented root suckering. The influence of stump sprouts could be replaced by applying IAA in lanolin paste to the cut surfaces of root stubs. These results provide additional support for an apical dominance theory of suckering. When IAA-2-C14 in lanolin was applied to the cut surfaces of root stubs, auto radiographs showed that Cl4 activity was concentrated where the majority of root suckers normally would develop. Apparently, IAA accumulated in this region and inhibited root suckering. When the IAA-lanolin paste was removed from the root stubs after inhibiting suckering for a month, vigorous root suckering took place. This indicated the possibility that black locust roots contain an IAA oxidase system. The existence of such a system was demonstrated by dialyzed enzyme preparations extracted from black locust roots which oxidized IAA in a Warburg apparatus.