General Botany Lab, EKU

COMPLEX FUNGI, LICHENS AND MYCORRHIZAE

Groups you will study today include the Ascomycota (the Ascomycetes) and the Basidiomycota (Basidiomycetes). The Conidial Fungi (which are also called Deuteromycetes or imperfect fungi), are Ascomycetes that rarely reproduce sexually.

Phylum ASCOMYCOTA , the Ascomycetes or Sac Fungi

The Sac Fungi (sometimes just called the ascos) is a group of non-aquatic fungi with regularly septate hyphae. (What do we mean by septate?). This group of fungi is named for the cell where where meiosis occurs, the ascus. The spores that develop in the ascus are called ascospores. Many diseases are caused by ascomycetes, from aspergillosis (a serious lung infection) to athletes foot, to chestnut blight and Dutch elm disease. On the positive side, most of the fungi in lichens are ascos, morels and truffles are ascos, and the species of Penicillium (sources of penicillin and bleu cheese) are ascos.

HEMIASCOMYCETES

The hemiascomycetes are the yeasts. The yeasts have no specialized structures. Their vegetative cells act as gametes and asci. Budding is how yeast cells reproduce asexually. Sexual reproduction in yeast occurs only occasionally.

YEAST CELLS

Note the prepared slide on demonstration . Notice the small size of these cells. Can you find any budding cells ? How is this type of yeast used commercially?

EUASCOMYCETES

The euascomycetes (euascos) enclose their asci in a special structure called an ascoma. Ascomas are formed from n + n hyphae. (See textbook, p. 271.) There are three main kinds of ascomas: (1) the cleistothecium (plural = cleistothecia) , which is a roundish, hollow ball that has no opening to the outside; (2) urn-shaped perithecia (singular = perithecium); and (3) wide-open cup-shaped apothecia (singular = apothecium). Asexual reproduction in euascomycetes is by fragmentation and conidiospores (= same thing as conidia).

CLEISTOTHECIUM. The powdery mildews have cleistothecia

Examine powdery mildew on oak leaves under the dissecting microscope on the side counter.

Note the mycelium, and the black cleistothecia.

Examine slide #15 from slide box B. This powdery mildew species infects lilacs and other plants. Find the following: mycelium, haustorial hyphae, cleistothecium, ascus, ascospores. If you look carefully, you might also see some conidia .

Examine the section of truffle tissue (permanent slide, scope on side counter). Tuber is the generic name of this unusual asco. The truffle fungus lives on oak tree roots and its cleistothecia develop underground. People use dogs and pigs to hunt truffles. Note that the asci are enclosed in the ascoma. Truffles are extremely expensive.

Why are dogs and pigs used to hunt truffles?

How do you think truffle spores are dispersed?

PERITHECIUM. Perithecia are jug-shaped or hollow structures with a single outlet.

FRESH MATERIAL
Obtain a few perithecia from the Sordaria culture provided and do a squash mount. The squash technique will force the asci out of the ostiole (= opening) of the perithecium. Note the perithecium, asci and ascospores.

How many ascospores does an ascus of Sordaria contain?

Examine the slide of Xylaria (slide #14 , slide box B). Xylaria ascomas have many perithecia imbedded in an elongated structure. Note these structures: perithecium, ascus, ascospores, and ostiole.

What is the common name of Xylaria and how did it get its common name?

APOTHECIUM. Apothecia are ascomas with cup-like or saucer-like openings.

On slide #13 (Peziza) note ascus, ascospores, and the hymenial layer . (A hymenial layer is a layer of hundreds to thousands of asci.)

Note the other examples of ascos on display.

Morels are considered to be an edible delicacy. What are some other common names for morels?

CONIDIAL FUNGI (= asexual Ascos)

Most reproduction is by abundant conidia (also called conidiospores). Some genetic recombination does occur, but usually not with gametes. Non-gametic genetic recombination is sometimes called parasexuality.

Examine the living culture of Penicillium chrysogenum (on side counter). This species of Penicillium is one of the main ones (along with P. notatum ) that produce penicillin (note the small droplets of fluid that contain penicillin). If you are allergic to penicillin, it is safe to handle the sealed culture.

Examine slides of Penicillium and Aspergillus (slides 16 and 17 in slide box B). Note the conidiophores and conidiospores. Some species of Aspergillus produce dangerous toxins (aflatoxin), and other species are used commercially (to make tofu, for instance).

Why do you think fungi produce substances like penicillin and aflatoxin?

Phylum BASIDIOMYCOTA , the Basidios or Club Fungi

Club Fungi have long-lived n + n mycelia and club-shaped sporangia called basidia. The Homobasidiomycetidae have well developed basidiomas that contain the basidia. The Heterobasidiomycetidae are parasitic rusts that lack basidiomas.

HOMOBASIDIOMYCETIDAE, the non-rust basidios (a very diverse group)

These are the mushrooms and other fleshy or woody fungi that most people recognize as fungi. They have obvious basidiomas.

LIVING MATERIAL

Examine a fresh mushroom ( Agaricus bisporus). This is the common mushroom used in salads and soups. Identify the stipe, inner veil, annulus, pileus (= cap) and lamellae (= gills). If you examine the gill surfaces carefully under high power of a dissecting microscope, you will see the basidiospores shining.

Note other fresh specimens that may be on display.

PRESERVED and/or DRIED MATERIAL

Examine the fungi specimens on the side counter. Note the variation in basidiomas. Some have pores, some have other kinds of hymenial surfaces, and some are resupinate (= lie flat on branches). Some of the specimens in jars are in the genus Amanita, a genus of very poisonous mushrooms. Species that convert most of the basidioma is converted to spores are called Gasteromycetes.

          What is the difference between a mushroom and a toadstool?

          Why would being poisonous or hallucinogenic be advantageous to a mushroom?

PERMANENT SLIDES

Examine the prepared slide (#19 , slide box B) of Coprinus. This slide is a cross section of the pileus of a small mushroom. Identify the gills, plectenchyma, hymenial layer, basidium, and basidiospores. Which structures are n+n and which structures are n? You might want to consult the life cycle diagram on p. 273 of your textbook.

WOOD ROTTING FUNGUS

On the side counter, note the following:

           Piece of firewood, showing rotted and unrotted wood.

           Permanent slide under microscope, showing secondary (n+n) mycelium in wood cells.

HETEROBASIDIOMYCETIDAE (Teliomycetes), the rusts

Rusts do not have a basidioma. They are obligate parasites, with two hosts. (The technical term for parasites with two dissimilar hosts is heteroecious = two houses.) Several of the Teliomycete rust fungi are important diseases of plants. We will consider wheat rust, Puccinia graminis, which continually threatens humanitys food supply.

Note the examples of rust disease life cycle stages. (on side counter)

WHEAT RUST (Puccinia)

Wheat rust has a complex life cycle. You probably will need to consult the life cycle diagram (p. 280-281, textbook) as you examine slides 20, 21, and 22.

          On slide #20 , you should be able to identify and understand the functions of the following-- spermogonium, spermatia, receptive hyphae, aecium, aeciospores.

          On slide #21 , you should note the following: uredinium, urediniospores .

          On slide #22 , you should note telium and teliospores.

You should be able to distinguish each of stages and their spores from each other.

Note the stages of wheat rust on display (dissecting microscope, side counter)

          On barberry leaves - spermagonia, aecia

          On wheat stems - uredinia, telia

Which structures in the life history of wheat rust are n, which are n + n, and which are 2n?

What role do each of the following play in the life cycle of wheat rust? -- basidiospore, aeciospore, urediniospore, teliospore, spermogonium.

When a parasite has two hosts, which is the definitive host and which is the alternate host?

MYCORRHIZAE

Examine the prepared slide on demonstration under a microscope on the side counter.  Can you see where the fungal hyphae are distributed? (Are they outside the root, inside the cortex, inside the cells, neither, or all of these?

What are the functions of mycorrhizae?

What is the probable evolutionary significance of the fungus-root relationship?

LICHENS

A lichen is a dual organism formed by a fungus and and one (or rarely more than one) species of algae. The fungus is usually an asco (rarely a basidio) and the alga is either a cyanobacterium or a green alga. Lichens containing cyanobacteria can and do fix nitrogen. Also, lichens are important pioneer soil-formers and are the basis of some arctic food chains.

LIVING LICHENS

When dry, lichens can exist indefinitely and become active again when they become wet.

Examine some samples of the three main kinds of lichens: crustose lichens, foliose lichens, and fruticose lichens. (side counter)

PREPARED SLIDE

Examine slide #18 , which is a section cut through a lichen, Physcia. Note the following: cortex, medulla, algal cells, rhizines, apothecium, hymenium, asci, ascospores, paraphyses. What are soredia? Can you see any soredia?

What was this lichen growing on? How do you know?