The most prevalent beneficial organisms associated with plants are soil-inhabiting fungi. "Mycorrhiza" is the general term used to describe various categories of mutualistic root-fungal partnerships that occur in the underground environment. This CD presents a detailed visual description of all mycorrhiza categories and is designed so that images can be uploaded into PowerPoint presentations for teaching and seminars. Most of the images are from our own research and many have been published in our book, Mycorrhizas: Anatomy and Cell Biology. This CD and book together represent the result of a long collaboration among Larry Peterson, Hugues Massicotte and Lewis Melville, and reflects our shared interest in exploring the structural diversity of mycorrhizas. The CD could not have been produced without the computer and design skills of Forrest Phillips. We thank Linda Tackaberry and Erin Zimmerman for editing the text.

Copyright

© 2006 National Research Council Of Canada
All rights reserved. No part of this publication may be reproduced in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada.

Cover Printed in Canada on acid-free paper.
ISBN 0-660-19404-X
NRC No. 46854

Library and Archives Canada Cataloguing in Publication
Mycorrhizas: anatomy and cell biology [electronic resource] / R. Larry
Peterson … [et al.].

Issued by National Research Council Canada.
CD-ROM format.
Originally issued 2004 in printed form as:
Peterson, R. Larry. Mycorrhizas: anatomy and cell biology.
Includes bibliographical references.
Includes index.
ISBN 0-660-19404-X
1. Mycorrhizas. 2. Mycorrhizal fungi. 3. Roots (Botany). I. Peterson, R. Larry II. Peterson, R. Larry Mycorrhizas: anatomy and cell biology. II. National Research Council Canada.

QK604.2.M92M92 2006                         79.5'17852                              C2006-980208-4 

The CD is organized by mycorrhiza category. Host plants and fungal symbionts involved in the association are given first, followed by general morphological and anatomical characteristics of the mycorrhiza. Detailed structural information obtained by light microscopy, scanning electron microscopy, transmission electron microscopy, and (or) laser scanning confocal microscopy is included. The CD is intended as a supplementary resource of images which can augment any course of study that deals with various aspects of mycorrhizas. For more in-depth coverage of the extensive literature on the structure and function of mycorrhizas, a list of references is provided below.

Mycorrhizal Categories

A brief definition of each mycorrhiza category is given here. More detailed descriptions are given for each category in the specific sub-directory along with the images.

Ectomycorrhizas are characterized by the formation, to varying degrees, of a fungal mantle on the root surface and Hartig net hyphae between root epidermal and cortical cells. These mycorrhizas predominantly occur on the roots of tree species. Numerous species of Basidiomycete fungi and fewer Ascomycete fungi are able to form ectomycorrhizas. As well, a few species in the genus Endogone (Zygomycetes) are known to form ectomycorrhizas.

Ectendomycorrhizas resemble ectomycorrhizas in that they possess a fungal mantle and Hartig net but differ in that, after Hartig net formation, intracellular hyphae develop in epidermal and cortical cells. They are confined to the conifer genera Pinus and Larix and are formed by a small group of Ascomycete fungi.

Arbuscular mycorrhizas (AMs) (formerly referred to as vesicular-arbuscular mycorrhizas; VAMs) are by far the most prevalent of all mycorrhizas and are estimated to include more than 85% of all plant species; the association involves a few fungal genera in the Phylum Glomeromycota. The most diagnostic feature of this mycorrhiza is the development of intercellular hyphae, intracellular hyphae, and arbuscules (hyphae with branching structures) in root cortical cells (some species also develop vesicles or swollen hyphal structures, within and between root cells). Spores may be produced on intraradical and extraradical hyphae, and certain genera may develop auxiliary cells (spore-like structures) in the extraradical mycelium.

Ericoid mycorrhizas are mainly found in the families Ericaceae and Epacridaceae of the angiosperm order Ericales. These mycorrhizas are extremely important in heathland ecosystems where soil nitrogen is bound in various organic compounds. The nitrogen in these compounds is accessed by the plant, primarily via the mycorrhizal fungi associated with fine roots. Epidermal cells of these "hair roots" are colonized by fungal hyphae which form intracellular hyphal complexes. The few identified fungal species belong mostly to the Ascomycota.

Monotropoid and Arbutoid/Pyroloid mycorrhizas are also found in several plant members of the Ericales; these specialized mycorrhizas differ from ericoid mycorrhizas in that they have a mantle and Hartig net, like ectomycorrhizas. Arbutoid/Pyroloid mycorrhizas also have intracellular hyphae restricted to the epidermis. In Monotropoid mycorrhizas, each epidermal cell is invaded by a single hypha forming a "peg" around which the host cell elaborates a wall and plasma membrane. The fungal partners include both Basidiomycete and Ascomycete fungi. Monotropoid mycorrhizas, however, may be restricted to the Basidiomycetes and some of the plant species appear to be highly specialized in terms of their fungal partners.

Cistoid mycorrhizas are a distinct group of mycorrhizas that, depending on the conditions under which plants are grown, share many of the attributes of ectomycorrhizas or arbutoid mycorrhizas. The Hartig net and intracellular hyphae, when present, colonize many cortical cell layers in addition to the epidermal cells. Cistoid mycorrhizas involve angiosperm genera (e.g., Cistus, Helianthemum, Hudsonia) in the family Cistaceae (order Malvales). The fungal associates include Basidiomycetes and Ascomycetes.

Orchid mycorrhizas are restricted to the large angiosperm family Orchidaceae and are unique in that symbiotic fungal associations occur with embryo cells of germinating seeds as well as with root cells of both seedlings and mature plants. In all situations, various fungal species belonging to the Basidiomycota form intracellular coils called "pelotons".

Mycorrhiza-like associations in "Bryophytes" are extremely diverse. In the liverworts (Hepatophyta), the gametophyte (the dominant photosynthetic phase), occurs in two morphological forms - thallose and leafy. Most of the thallose species are associated with Glomalean fungi; intracellular structures including hyphae, arbuscules and vesicles usually form. However, four genera of thallose liverworts are associated with Basidiomycetes. In these, intracellular hyphal structures similar to those occurring in orchids are formed.

Leafy liverworts are associated with either Ascomycetes or Basidiomycetes. In the former, rhizoid tips are swollen, and these are occupied by hyphal coils. In species associated with Basidiomycetes, intracellular fungal coils develop in some stem cells while adjacent uncolonized cells develop pegs of host wall material encasing fungal hyphae.

Dark septate fungal endophytes, while not considered to be mycorrhizas, have been included because these fungi associate with many plant roots and are highly prevalent in various ecosystems. It has been demonstrated that some may form mutualistic relationships with some plant species. A long list of plants (including dicotyledonous and monocotyledonous angiosperms, gymnosperms, ferns, and other seedless vascular plants) appear to be involved. Identifying the fungal species has been problematic because of their often sterile condition in culture; three Phialocephala species as well as Chloridium paucisporum and Leptodontidium orchidicola have been identified. Dark and (or) hyaline hyphae enter roots, proliferate between or within cells, and sometimes form microsclerotia within epidermal and cortical cells.

Recent specialized books on mycorrhizas

Allen, M.F. (ed). 1992. Mycorrhizal Functioning, An Integrative Plant Fungal Process. Chapman & Hall, New York, USA.

Brundrett, M., Bougher, N., Dell, B., Grove, T., and Malajczuk, N. 1996. Working with Mycorrhizas in Forestry and Agriculture. The Australian Centre for International Agricultural Research (ACIAR) Monograph 32. Canberra, Australia.

Brundrett, M., Melville, L., and Peterson, L. (eds). 1994. Practical Methods in Mycorrhiza Research. Mycologue Publications, Waterloo, Canada.

Cairney, J.W.G., and Chambers, S.M. (eds). 1999. Ectomycorrhizal Fungi, Key Genera in Profile. Springer-Verlag, Berlin, Germany.

Fortin, J.A., Charest, C., and Piché, Y. 1995. La symbiose mycorhizienne, État des connaissances. Orbis Publishing.

Kapulnik, Y., and Douds, D.D. Jr. (eds). 2000. Arbuscular Mycorrhizas: Physiology and Function. Kluwer Academic Publishers, Dordrecht, The Netherlands.

Norris, J.R., Read, D.J., and Varma, A.K. (eds). 1991. Methods in Microbiology, Vol. 23. Techniques for the Study of Mycorrhiza. Academic Press, London, UK.

Peterson, R.L., Massicotte, H.B., and Melville, L.H. 2004. Mycorrhizas: Anatomy and Cell Biology. NRC Research Press. Ottawa, Canada.

Pfleger, F.L., and Linderman, R.G. (eds). 1994. Mycorrhizae and Plant Health. APS Press, St.Paul, USA.

Podila, G.K., and Douds, D.D. Jr. (eds). 2000. Current Advances in Mycorrhizae Research. APS Press, St. Paul, USA.

Rasmussen, H.N. 1995. Terrestrial Orchids from Seed to Mycotrophic Plant. Cambridge University Press, Cambridge, UK.

Read, D.J., Lewis, D.H., Fitter, A.H., and Alexander, I.J. (eds). 1992. Mycorrhizas in Ecosystems. C.A.B. International, Wallingford, UK.

Robson, A.D., Abbott, L.K., and Malajczuk, N. (eds). 1994. Management of Mycorrhizas in Agriculture, Horticulture and Forestry. Kluwer Academic Publishers. Dordrecht, The Netherlands.

Sharma, A.K., and Johri, B.N. (eds). 2002. Arbuscular Mycorrhizae. Interactions in Plants, Rhizosphere and Soils. Science Publishers, Inc. Enfield, N.H. USA.

Smith, S.E., and Read, D.J. 1997. Mycorrhizal Symbiosis. Second Edition. Academic Press. San Diego, USA.

Smith, S.E., and Smith, F.A. (eds). 2002. Diversity and Integration in Mycorrhizas. Kluwer Academic Publishers, Dordrecht, The Netherlands.

Varma, A. (ed). 1998. Mycorrhiza Manual. Springer-Verlag, Berlin, Germany.

Varma, A., and Hock, B. (eds). 1998. Mycorrhiza Structure, Function, Molecular Biology. Springer-Verlag, Berlin, Germany.