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Keywords:

  • arbuscular mycorrhiza;
  • epidermal block;
  • grafting;
  • low nodulator;
  • pea mutant;
  • restriction of fungal entry;
  • root symbiosis;
  • shoot regulation

Summary

  •  E107 is a pleiotropic mutant of Pisumsativum (pea) characterized by a decreased ability to form nodules. Its colonization by the arbuscular mycorrhizal fungus Glomusaggregatum is reported, and the mycorrhizal phenotype compared with the nodulation phenotype.
  •  Four cleared lateral roots from 21-d-old plants were chosen randomly, and their lengths scanned for any fungal structures. Colonization success was determined by counting the numbers of extraradical hyphae, and calculating epidermal entry and cortical entry. Graft experiments were performed to establish which organ regulates mycorrhiza-formation.
  •  Two blocks to infection were obvious, at the root surface, and at the interface between the epidermis and the outermost cortical cell layer. Once the fungus breached this interface, it spread within the cortex and formed normal arbuscules. The mutant phenotype was controlled by the shoot.
  •  The E107 mycorrhizal phenotype was designated as app+, low pen, low coi. The development of the fungal infection was similar to that of rhizobial infection and under the same shoot control. The phenotype of the mutant E107 strongly supports the hypothesis that mycorrhiza formation and nodulation are regulated by the same processes.