Planta

, Volume 211, Issue 5, pp 722-728

First online:

Root hair elongation is inhibited by hypaphorine, the indole alkaloid from the ectomycorrhizal fungus Pisolithus tinctorius, and restored by indole-3-acetic acid

  • Franck Anicet DitengouAffiliated withEquipe de Microbiologie Forestière, Centre de Recherches de Nancy, Institut National de la Recherche Agronomique, F-54280 Champenoux, France
  • , Thierry BéguiristainAffiliated withEquipe de Microbiologie Forestière, Centre de Recherches de Nancy, Institut National de la Recherche Agronomique, F-54280 Champenoux, France
  • , Frédéric LapeyrieAffiliated withEquipe de Microbiologie Forestière, Centre de Recherches de Nancy, Institut National de la Recherche Agronomique, F-54280 Champenoux, France

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Abstract.

Hypaphorine, the major indolic compound isolated from the ectomycorrhizal fungus Pisolithus tinctorius, controls the elongation rate of root hairs. At inhibitory concentrations (100 μM), hypaphorine induced a transitory swelling of root hair tips of Eucalyptus globulus Labill. ssp. bicostata. When the polar tip growth resumed, a characteristic deformation was still visible on elongating hairs. At higher hypaphorine concentrations (500 μM and greater), root hair elongation stopped, only 15 min after application. However, root hair initiation from trichoblasts was not affected by hypaphorine. Hypaphorine activity could not be mimicked by related molecules such as indole-3-acetic acid (IAA) or tryptophan. While IAA had no activity on root hair elongation, IAA was able to restore the tip growth of root hairs following inhibition by hypaphorine. These results suggest that hypaphorine and endogenous IAA counteract in controlling root hair elongation. During ectomycorrhiza development, the absence of root hairs might be due in part to fungal release of molecules, such as hypaphorine, that inhibit the elongation of root hairs.

Key words: Hypaphorine – Ectomycorrhiza (signal) – Indole-3-acetic acid – Root hair – Tryptophan betaine