The relationship between rooting of poplar shoots and ATPase activity of their crude microsomal vesicles

Poplar shoots raised in vitro were induced to root by a 7 h passage on an auxin(1-naphthaleneacetic acid) medium. The percentage of rooting was reduced from +/- 97% to +/- 47% when vanadate (200 mu M) was included in the auxin medium. Introduction of vanadate in the medium without auxin after the 7 h induction on auxin medium, did not inhibit rooting but affected only the development of the roots produced. The Mg2+-dependent ATPase activity of the microsomal vesicles of poplar shoots was increased after 7 h induction on rooting medium and corresponded to an increase in the Vmax of the enzyme. Results from experiments using some inhibitors of the polyamine metabolism suggested that this pathway was not involved in the increase of this activity. The auxin had no effect on the in vitro ATPase activity at any concentration tested except at about 2 mM where it was inhibitory, probably due to a change in the conformation of the enzyme. The transient increase of indole-3-acetic acid during rooting induction could be responsible for the increase in the level of the enzyme. The inhibition of root formation and growth by vanadate indicates strongly that the ATPase activity may be necessary for the induction and expression of rooting.