Imhof, S. & Weber, H. Chr. (2000):
Root structures and mycorrhiza of the achlorophyllous Voyria obconica Progel (Gentianaceae).
Symbiosis 29: 201 - 211.
- The genus Voyira comprises 19 achlorophyllous, mycotrophic
species with reduced cormi. Roots of Voyria obconica are up to
1 cm long, 1 - 1.5 mm thick, succulent, brittle and radiated from the
shoot base, forming a star-shaped root system. In cross section the
central cylinder consists of up to 10 central vessels, surrounded by
some parenchymatous cells, 5 to 7 strands of phloem and a pericycle.
The cell walls of the anatomically inconspicuous endodermis are
characterised by a faint suberin lamella. The cortex is divided into an
inner cortex, with 3 to 5 layers of longitudinally elongated cells and
a multilayered outer cortex, comprising isodiametric cells. The 2-3
cell layers of the dermal tissue also show a faint suberin lamella
within their thickened cell walls. Non-parasitic, achlorophyllous
plants need symbiotic interactions with mycorrhizal fungi. In V.
obconica the exclusively intracellular hyphae of a single
mycorrhizal fungus grows after penetration of the dermal tissue
straight towards the inner cortex. Within the inner cortex the hyphae
proceed parallel to the central cylinder. Branches of these straight
inner cortex hyphae then colonize the outer cortex, where they form
coils, swell, and eventually degenerate to amorphous clumps.
Similarities and differences in root structure and mycorrhiza to the
closely related Voyria tenella are elucidated. Arguments are
given to call this association a special form of a Paris-type
arbuscular mycorrhiza. The ecological significance of the revealed
mycorrhizal compartmentation is discussed.
Key words: Voyria, Gentianaceae, root anatomy, root morphology, mycorrhiza, myco-heterotrophy.