Mycorrhizal colonization of root cortex water storage cells of epiphytic orchids

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Abstract

In contrast to terrestrial species, epiphytic orchids possess water storage elements as an adaptation to dry habitats. Tracheoidal elements are present in roots and are involved in the interaction with mycorrhizal fungi, which colonize orchid roots obligately. Lignified water storage cells are located in the cortex and perform the functional role of water storage. Among the lignified exodermis cells, thin-walled passage cells are present. These elements are essential for the exchange of water between the root and the environment. This study supports existing data indicating that passage cells are the only exodermis cells through which fungal hyphae can pass. It also presents evidence of water storage cells being colonized by mycorrhizal fungi and shows that lignified elements of cortex are less conducive to peloton formation than thin-walled cortex cells.

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About the authors

N. M. Bibikov

Faculty of Biology, Lomonosov Moscow State University

Author for correspondence.
Email: bibik0808@mail.ru
Russian Federation, Moscow

E. Yu. Voronina

Faculty of Biology, Lomonosov Moscow State University

Email: bibik0808@mail.ru
Russian Federation, Moscow

A. K. Eskov

Faculty of Biology, Lomonosov Moscow State University

Email: bibik0808@mail.ru
Russian Federation, Moscow

M. Ignatov

Faculty of Biology, Lomonosov Moscow State University; Tsitsin Main Botanical Garden of the Russian Academy of Sciences

Email: bibik0808@mail.ru
Russian Federation, Moscow; Moscow

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Supplementary files

Supplementary Files
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1. JATS XML
2. Fig. 1. Anatomy of fungal colonization in substrate roots of epiphytic orchids. A — Thrixspermum sp. root on transverse section (ab — abaxial side, ad — adaxial side, v — velamen, ex — exodermis, wc — water storage cell, arrowheads point at colonized cortex cell, double arrowheads point at colonized WSC); B — root of Epidendroideae gen. sp. 4 on transverse section (h — fungal hyphae in velamen, ex — exodermis, pc — passage cell, dp — degraded peloton); C — root of Epidendroideae gen. sp. 4 on transverse section (fp — intact peloton); D — root of Epidendroideae gen. sp. 4 from abaxial side on longitudinal section (rh — root hair, v — velamen, ex — exodermis, arrowheads point at fungal hyphae in root hair and velamen, double arrowheads point at colonized PCs). Scale bars: A — 200 μm, B — 50 μm, C — 40 μm, D — 100 μm.

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3. Fig. 2. Confocal images of colonized water storage cells in roots of studied plants. A — Epidendroideae gen. sp. 3; B — Epidendroideae gen. sp. 4; C — Epidendroideae gen. sp. 5; D — Thrixspermum sp. Arrows point at WSCs with fungal pelotons. Scale bars: A — 100 μm; B — 180 μm, C — 200 μm, D — 60 μm.

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4. Fig. 3. Shares of colonized thin-walled cortex cells from total amount of thin-walled cortex cells (orange columns) and colonized WSCs from total amount of WSCs (yellow columns).

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5. Fig. 4. Fluorescence images showing colonized PCs (arrowheads) on longitudinal sections.

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