Altered carbon delivery from roots: rapid, sustained inhibition of border cell dispersal in response to compost water extracts

Background and aims: In a previous study, a compost water extract (CWE) applied to pea seedlings resulted in >95 % protection against root infection. The protection was correlated with retention of a sheath of root border cells surrounding each root tip. A transient exposure to CWE was correlated with 80 % reduction in infection, and with retention of border cell sheaths. Early effects of CWE on border cell dispersal therefore were examined.

Materials and methods: Temporal and spatial dynamics of pea, maize, cotton, and cucumber border cell dispersal into water or CWE were measured.

Results: Border cells formed a mass surrounding root tips within seconds after exposure to water, and most cells dispersed into suspension spontaneously. In CWE, >90 % of the border cell population instead remained appressed to the root surface, even after vigorous agitation. In cotton, for example, >25,000 border cells dispersed within seconds of immersion in water, but <100 border cells dispersed after >24 h in CWE.

Conclusions: Border cells can contribute >90 % of carbon released from young roots, and a single border cell can trap hundreds of bacteria within minutes. The impact of altered border cell dispersal on soil properties, plant nutrition, and root disease development warrants further study.