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Studies ON THE MYCORRHIZAS OF PINUS SYLVESTRIS L. PRODUCED IN VITRO WITH THE BASIDIOMYCETE SUILLUS VARIEGATUS (Sw. ex Fr.) O. KUNTZE: II. ULTRASTRUCTURAL ASPECTS OF THE ENDODERMIS AND VASCULAR CYLINDER OF THE MYCORRHIZAL ROOTLETS

Author:
WARMBRODT, ROBERT D., ESCHRICH, WALTER
Source:
The new phytologist 1985 v.100 no.3 pp. 403-418
ISSN:
0028-646X
Subject:
Pinus sylvestris, Suillus variegatus, apical meristems, ectomycorrhizae, electron microscopy, endodermis, parenchyma, sieve elements, tracheids, transpiration
Abstract:
The structure and development of the endodermis and vascular cylinder of ectomycorrhizas of Pinus sylvestris L. formed in vitro with the basidiomycete Suillus variegatus (Sw. ex Fr.) O. Kuntze were studied by light and electron microscopy. With the exception of the sieve elements, the cells of the vascular cylinder and endodermis differentiate relatively close to the apical meristem of the slow growing mycorrhizal rootlets. The endodermis is uniseriate and delimits a vascular cylinder which in most cases is diarch. All endodermal cells develop casparian strips in their anticlinal walls and approximately 50% of them undergo no further changes. The walls of the remaining endodermal cells however, are apparently impregnated with suberin or lipid‐like substances and these cells subsequently disintegrate and collapse. The vascular cylinder of the mycorrhizal rootlets consists of a mostly uniseriate pericycle, tracheids with circular‐bordered pits, sieve cells, variable numbers of vascular parenchyma cells and peripheral phloem parenchyma cells, the so‐called precursory phloem cells. The latter are characterized by high numbers of microfilament bundles and numerous, large aggregates of plasmodesmata which occur in thickened regions of the wall. Upon maturation of the sieve cells, the peripheral phloem parenchyma cells disintegrate and may eventually collapse. Typical albuminous (Strasburger) cells were not encountered in the material examined. By consideration of the structure and distribution of plasmodesmata among the various cell types the feasibility of symplastic and apoplastic transport within the mycorrhizal rootlets is discussed.
Agid:
484048