Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 4, 1998
Publication Date: N/A
Interpretive Summary: This paper examines how the loss of various plant parts effects the growth of root buds of the noxious perennial weed, leafy spurge. Also, this paper looks at the effects of the plant hormone auxin and inhibitors of auxin transport since previous reports suggest it plays a role in root bud growth. The findings of this work are that there appear to be two separate sources of signals which control root bud growth. One signal is generated by the loss of the leaves, and the other appears to be generated by the loss of actively growing meristems. Both leaves and meristems must be removed in order to get maximal root bud growth. Also, it was determined that auxin could inhibit root bud growth, but that auxin transport inhibitors had little effect on the root buds. This indicates that if auxin is one of the signals controlling root bud growth, it is not transported down the plant via the classic polar auxin transport system.
Localization of the source of the signal(s) controlling correlative inhibition of leafy spurge root buds was studied by sequential removal of various plant organs. It was determined that maximal release of root buds from correlative inhibition was achieved when plants had lost all aerial tissue, or had lost all aerial tissue except the stem and crown. Loss of only the apical meristem or loss of all growing and quiescent meristems (including stem and crown buds) did not result in a release of the root buds from correlative inhibition. Removal of the apical meristem and leaf tissue did result in growth of some root buds provided the root buds were exposed above soil level. These data indicate that the primary signal acting to maintain correlative inhibition of the root buds can be overcome by other environmental conditions (exposure to light and/or air) if the plants have first lost their leaves. Studies with naphthalene acetic acid (NAA), a synthetic auxin, indicated that applied auxin would maintain correlative inhibition of the root buds provided it was applied directly to the roots. When applied to the crown, NAA did not prevent root bud growth. These data are consistent with the possibility that auxin plays a role in maintenance of correlative inhibition of root bud growth in leafy spurge, but that free auxin transport is limited. Application of the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) around the base of the crown had no effect on root bud dormancy. The results of the auxin transport inhibitor studies suggest that correlative inhibition of root bud growth does not rely on the classic polar auxin transport system.