A paper out of the Hawes Lab noted that root border cells respond to or probe the surrounding soil by releasing a multitude of proteins, amino acids, sugars and secondary metabolites, and they do so even after the cells detach from the root cap. This material, called exudates, appears to alter the surrounding rhizosphere community of microorganisms. Curlango-Rivera et al., (2010) investigated the consequence of these plant exudates on the growth and production of root border cells. Exposure to pisatin, at concentrations capable of inhibiting fungal growth, stimulated production of root border cells, while exposure to a plant cell wall component, ferulic acid, inhibited growth of root border cells. Pisatin is a phytoalexin, a secondary metabolite made by the plant to limit microbial attack.
Does this indicate that plant root investment in root border cells as sensory organs occurs under the protective influence of a plant phytoalexins, but that cell wall fragments resulting from the rupture of root cap cells under microbial attack may limit plant root border cell proliferation? I am curious about experimental results if simultaneous exposure to the compounds occurred? Ferulic acid is often bound to a matrix of polymer structures found in plant cell walls. Would it take time for diffusion of these compounds into the rhizosphere to gain concentrations able to impart a biological effect?