Botany Blog Plants of the Northeastern U.S.

February 28, 2010

Dark Septate Endophytes

Filed under: Mycorrhizae — admin @ 02:49

Dark septate endophytes (DSE) are a heterogenous group of conidial or sterile fungi (thought to be ascomycetes) with darkly-pigmented, septate hyphae that commonly colonize plant roots. Most DSE also produce intracellular structures called microsclerotia. It has been suggested that these microsclerotia may serve as dispersal structures (Currah et al., 1993), although the actual purpose appears to be unknown. Perhaps they serve a storage function for the fungi as do the vesicles of AM fungi?

The following images show septate hyphae of a DSE growing in and around a root of Eurybia divaricata. The first image shows net-like strands formed by the hyphae of a DSE:

DSE covering a root of White Wood Aster

 The next image depicts several hyphae ending in microsclerotia, which appear as grape-like clusters.

Dark septate hyphae and miscrosclerotia

Another  morphotype can be seen with a root of Maianthemum racemosum in the following image:

Microsclerotia in a root of False Solomon’s Seal

The taxonomy of this group is poorly understood and little is known of the role that DSE play in natural ecosystems (see review by Jumpponen and Trappe 1998). DSE are difficult to identify from field samples so many may not yet be known. A few of the species identified to date (mostly from bioassays) include Chloridium paucisporum, Leptodontidium orchidicola, Phialocephala dimorphosphora, Phialocephala fortinii, and Phialophora finlandia. Of these, Phialocephala fortinii appears to be the best studied. Unlike AM fungi, the DSE that have been studied to date do not require a plant host and many can be grown as pure cultures.

Available evidence suggests that DSE range from strongly pathogenic to non-pathogenic to mycorrhizal for plants. Some strains of DSE may be involved in host plant nutrient acquisition and it has been proposed that this may be a mutualistic, mycorrhiza-like relationship (Jumpponen and Trappe 1998). These relationships do not appear to be host specific (Jumpponen and Trappe 1998), with some strains forming ectendomycorrhizas but also associating with other hosts in ways not completely understood (Jumpponen 2001).

Although their mycorrhizal status is uncertain (Jumpponen and Trappe 1998), DSE are commonly associated with the roots of herbaceous and woody plants from alpine, boreal and northern temperate ecosystems (Haselwandter and Read 1980, Holdenrieder and Sieber 1992; O’Dell et al. 1993; Ahlich and Sieber 1996). To date, carbohydrate flow from a host plant to a DSE has not yet been demonstrated as it has for AMF (Jumpponen 2001). Despite their ubiquity in terrestrial ecosystems, the role of DSE in plant nutrient acquisition and plant community assemblage remains largely unknown. Given the ubiquity of DSE in many terrestrial ecosystems and their possible mycorrhiza-like relationships with plants, studying this group of fungi could increase our understanding of plant community assemblage.

Literature Cited:

Ahlich, K. and T.N. Sieber. 1996. The profusion of dark septate endophytic fungi in non-ectomycorrhizal fine roots of forest trees and shrubs. New Phytologist 132:259-270.

Currah, R.S., Tsuneda, A., and Murakami, S. 1993. Morphology and ecology of Phialocephala fortinii in roots of Rhododendron brachycarpum. Canadian Journal of Botany 71:1639-1644.

Haselwandter, K. and D.J. Read. 1980. Fungal associations of roots of dominant and sub-dominant plants in high-alpine vegetation systems with special reference to mycorrhiza. Oecologia 4:557-62.

Holdenrieder, O. and T.N. Sieber. 1992. Fungal associations of serially washed healthy non-mycorrhizal roots of Picea abies. Mycological Research 96:151-156.

Jumpponen, A. and J.M. Trappe. 1998. Dark septate endophytes: a review of facultative biotrophic root-colonizing fungi. New Phytologist 140:295-310.

Jumpponon, A. 2001. Dark septate endophytes – are they mycorrhizal? Mycorrhiza 11:207-211.

O’Dell, T.E., H.B. Massicotte and J.M. Trappe. 1993. Root colonization of Lupinus latifolius Agardh. and Pinus contorta Dougl. By Phialocephala fortinii Wang & Wilcox. New Phytologist 124:93-100.

February 24, 2010


Filed under: Uncategorized — admin @ 02:04

Plant cells rely on internal hydrostatic pressure to maintain their shape. This pressure is maintained by a relatively high solute concentration inside the vacuole, which results in the absorption of water from outside the cell via osmosis (Raven et al., 2007). As the vacuole swells with water, the protoplast increases in size and the plasma membrane pushes up against the inside of the cell wall, resulting in turgor pressure. The turgor pressure is counteracted by the call wall and these opposing forces help maintain the shape of the cell and ultimately support herbaceous plant tissues.

The image below show cells in a leaf of Elodea canadensis that was placed in a solution of distilled water. The small green structures are the chloroplasts inside the cells and notice that they are distributed near the cell wall.

 Normal Plant Cell

Elodea cell in a solution of distilled water

If a plant does not receive sufficient water or is placed in environment that is hypertonic (one that has a higher solution concentration than the plant cells, e.g. a salty environment), than the cells will lose water and the plants will wilt. This is because water will be drawn out of the vacuole through osmosis, the protoplast will shrink, and the plasma membrane will actually pull away from the cell wall (plasmolysis), resulting in a loss of turgor pressure.

The following image shows an Elodea leaf that was placed in a 20% sucrose (sugar) solution. Note how the inside of the cell is shrinking and the gap between the plasma membrane and the cell wall (the cell wall does not shrink because it is somewhat rigid due to the presence of cellulose microfibrils).

Plasmolysed plant cell

 Elodea cell in a solution of 20% sucrose

Literature Cited

Raven, P.H., Evert, R.F., and S.E. Eichhorn. 2007. Biology of Plants, 7th ed. Worth Publishers, Inc., NY.

February 8, 2010

Eastern Comma

Filed under: Plant-Insect Interactions — admin @ 22:25

Spring semester is in full swing so it has been difficult to find time to write of late. I shot this image of an Eastern Comma (Polygonia comma) last summer as it was resting on a bench along the boardwalk that leads into a poor fen here in central NY.

Eastern Comma

This butterfly occurs throughout most of the eastern half of the United States and has two broods a year. The larvae will feed on a variety of host plants including False Nettle (Boehmeria cylindrica), Wood Nettle (Laportea canadensis), American Elm (Ulmus americana) and Stinging Nettle (Urtica dioica). Adults feed on the sap of trees (Layberry et al. 1998).

Literature cited:

Layberry, R.A., Hall, P.W., and Lafontaine, J.D. 1998. The Butterflies of Canada. University of Toronto Press.

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