Soybean root growth inhibition and lignification induced by p-coumaric acid
2009
Zanardo, Daniele Iara Lucca | Lima, Rogério Barbosa | Ferrarese, Maria de Lourdes Lucio | Bubna, Gisele Adriana | Ferrarese-Filho, Osvaldo
The effects of 0.25-2mM p-coumaric acid, a phenylpropanoid metabolite with recognized allelopathic properties, were tested on root growth, cell viability, phenylalanine ammonia-lyase (PAL) activities, soluble and cell wall-bound peroxidase (POD) activities, hydrogen peroxide (H₂O₂) level and lignin content and its monomeric composition in soybean (Glycine max (L.) Merr.) roots. At >=0.25mM, exogenously supplied p-coumaric acid induced premature cessation of root growth, increased POD activity and lignin content and decreased the H₂O₂ content. At >=0.5mM, the allelochemical decreased the cell viability and PAL activity. When applied jointly with PIP (an inhibitor of the cinnamate 4-hydroxylase, C4H), 1mM p-coumaric acid increased lignin content. In contrast, the application of MDCA (an inhibitor of the 4-coumarate:CoA ligase, 4CL) with p-coumaric acid did not increase lignin content. The lignin monomeric composition of p-coumaric acid-exposed roots revealed a significant increase of p-hydroxyphenyl (H) and guaiacyl (G) units. Taken together, these results suggest that p-coumaric acid's mode of action is entry via the phenylpropanoid pathway, resulting in an increase of H and G lignin monomers that solidify the cell wall and restrict soybean root growth.
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