Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 1999
Publication Date: N/A
Interpretive Summary: Leafy spurge is a perennial weed that maintains a prodigious number of underground axillary buds on its extensive root system. Either leaves or growing axillary buds on the stems of leafy spurge can prevent growth of underground adventitious shoot buds (often referred to as root buds). As few as three leaves left on an otherwise naked stem can significantly reduce root bud growth. However, although leaves seem to prevent or reduce growth of the root buds, they have little effect on the number of root buds that grow. Both light and CO2 are required for the leaves to inhibit root bud growth. This means that photosynthesis is likely to be directly or indirectly involved in production of the leaf derived signal. The plant hormone gibberellic acid increases root bud growth on all plants treated with this compound, but it has a significantly greater effect on plants with leaves, but which lack growing axillary buds. This means that leaves might act by inhibiting the production of gibberellic acid in the root buds.
Earlier studies on the source of signals controlling correlative inhibition of root buds (underground adventitious shoot buds located on the lateral roots) in leafy spurge (Euphorbia esula L.) indicated that either growing meristems (apical or axillary buds) or leaves could prevent root buds from breaking quiescence. As few as three leaves remaining on budless stems will greatly reduce the growth of (but not the number of growing) root buds. Also, light and CO2 fixation are necessary for the leaf effects on root bud growth, but not necessary for correlative inhibition imposed by growing axillary buds. Treatment of plants with atrazine induces root bud growth on budless plants but not on plants with intact axillary buds. The polar auxin transport inhibitor NPA prevents transmission of the signal from growing axillary buds, but has only a minor effect on the transmission of the leaf-derived signal. Treatment of plants with gibberellic acid (GA) induces growth of root buds under otherwise non-inducing conditions to some extent in all plants. However, GA has its greatest effects on plants with intact leaves (budless and meristemless). GA has no significant effect on root bud quiescence under conditions which induced root bud growth.