Long-term control of leafy spurge with glyphosate requires multiple
applications because the plant reproduces vegetatively from abundant
underground adventitious buds, referred to as crown and root buds.
Determining the molecular mechanisms involved in controlling vegetative
reproduction in leafy spurge following foliar glyphosate treatment could
identify limiting factors or new targets for manipulation of plant growth
and development in invasive perennial species. Thus, we treated leafy spurge
plants with 0 or 2.24 kg ai ha−1 glyphosate to determine its
impact on selected molecular processes in crown buds derived from intact
plants and plants decapitated at the soil surface 7 d after glyphosate
treatment. New shoot growth from crown buds of foliar glyphosate-treated
plants was significantly reduced compared with controls after
growth-inducing decapitation, and had a stunted or bushy phenotype.
Quantification of a selected set of transcripts involved in hormone
biosynthesis and signaling pathways indicated that glyphosate had the most
significant impact on abundance of ENT-COPALYL DIPHOSPHATE
SYNTHETASE 1, which is involved in a committed step for
gibberellin biosynthesis, and auxin transporters including PINs,
PIN-LIKES, and ABC TRANSPORTERS. Foliar
glyphosate treatment also reduced the abundance of transcripts involved in
cell cycle processes, which would be consistent with altered growth patterns
observed in this study. Overall, these results suggest that interplay among
phytohormones such as auxin, ethylene, and gibberellins affect vegetative
growth patterns from crown buds of leafy spurge in response to foliar
glyphosate treatment.