Structure of root nodules in <i>Laburnum anagyroides</i> Medik.

Abstract

The structure of the <i>Laburnum anagyroides</i> root nodules was studied by means of classical light and transmission electron microscopy methods. The ability of cross-inoculation and effective nodulation by rhizobial microsymbionts, effective in other genistean species, was not confirmed in <i>L. anagyroides</i>. However, the seedlings were successfully albeit ineffectively nodulated by non-identified rhizobia from soil sampled under established <i>L. anagyroides</i> trees. The microscopic (ultra)structure of these nodules met the basic criteria of genistoid nodules: their meristem was apically positioned and contained two domains (infected and non-infected one), non-bacteroidal rhizobia persisted in apoplast enclaves, and intra-nodule rhizobial infection was passed from cell to cell by host cell division and not by infection threads. The developmental disturbances detected in the nodules (primarily, formation of multi-bacteroid sacs instead of typical single-bacteroid symbiosomes and proliferation apoplast enclaves with accompanying cell wall discontinuities) suggested that the host plant incorrectly recognized the microsymbiont used in the present study.