Exercise A Fungal Diversity

Fungus-like organisms occur in both the Kingdom Protista and the Kingdom Fungi. In this lab, wc will look at several groups of organisms in rhe Kingdom Fungi. The Division Zvgomycota includes a large group of fungi that have very simple structures. There are rwo characteristic reproductive structures in this group. The asexual reproductive structure is the sporangium, within which asexual spores arc produced. The sporangium (pi. sporangia) develops on a specialized hvpha called a sporangiophore (tig. 18.1 a). The sexual reproductive structure is the zygospore (tig. 18.16), which results from the fusion of compatible gamctangia. The common black bread mold, RJjizopus stolonifcr, is a member of this division. One group of fungi in the Zvgomycota produce mycorrhizae, a symbiotic association between a fungus and the roots a of plant. The mvcobiont (fungal partner in the associ-

Sporangia

Sporangiophore

Sporangiophore

Zygospore
Rhizpus Zygospores Structure

FIGURE I 8.1 RHIZOPUS. A MEMBER OF THE ZYGOMYCOTA. (A) SPORANGIA. ASEXUAL REPRODUCTIVE STRUCTURES. (B) ZYGOSPORE. A SEXUAb REPRODUCTIVE STRUCTURE.

Vesicular Arbuscular Mycorrhiza
FIGURE 18.2 VESICULAR-ARBUSCULAR (VA) MYCORRHIZAE. AN ARBUSCULE IS VISIBLE WITHIN THE PLANT CELL.

at ion) aids in mineral uptake (especially phosphorus), and the plant furnishes carbohydrates for use by the fungus. It has been estimated that 95; • of all vascular plants have mycorrhizal. Although several different types of mycor-rhizae exist, the mycorrhizal fungi in the Zygomycota arc-known as vesicular-arbuscular (VA) mycorrhizac. They produce highly branched structures called arbusculcs within the plant cell fig. 18.2). The cxchangc of nutrients occurs through these arbusculcs.

Members of the Division Ascomycota produce sexual spores called ascospores within a saclike structure called an ascus. There are 8 ascosporcs within each ascus. Some members of this division are microfungi (microscopic fungi), while others producc a large fruiting body (reproductive structure). Among those with fruiting bodies arc the morels and cup tungi (tig. 18.3/7); the depressions on these fruiting bodies arc lined with asci (tig. 18.3/;). Most yeasts belong to the Ascomycota, but they do not producc a fruiting body.

In the Division Basidiomycota, the fungi producc sexual spores that are called basidiospores. These arc produced externally on a basidium (pi., basidia). Four basidiospores are produced on each basidium. Basidia line the gills of mushrooms and the pores of brackcr tungi 1 tig 18.4). In addition to mushrooms, bracket fungi, and puflballs, the Basidiomycota includes two groups of plant pathogens—the rust fungi and the smut fungi. These pathogens, which lack fruiting bodies, cause billions of dollars of crop losses each year.

The most common fungi in the environment are a large group of asexual fungi whose sexual stage is unknown. They grow easily on most substrates and are commonly called molds. Most are believed to be members of the Ascomycota even though the sexual stage has not been identified. They form asexual spores called

Asexual Spores Ascomycota

FIGURE 18.3 MORELS ARE MEMBERS OF THE ASCOMYCOTA. (A) FRUITING BODIES. (B) ASCOSPORES WITHIN THE ASCUS.

FIGURE 18.3 MORELS ARE MEMBERS OF THE ASCOMYCOTA. (A) FRUITING BODIES. (B) ASCOSPORES WITHIN THE ASCUS.

conidia sing., conidium i on structures called conidio-phorcs (specialized hyphac that give rise ro conidia). Asexual fungi occur in the soil, on leaf surfaces, and on contaminated foods and building materials. The spores arc dispersed by wind, and they can easily be isolated from the air.

Materials Needed for Exercise A

Compound and dissecting microscopes

Cultures of Rhizopus, Pttiicillium, and Aspergillus (do nor open the lid)

Cup fungi and morels

Far of corn infected with Ustilago vtnydis

Prepared slide of 9 mushroom gill

Prepared slide of Pcziza asci

Basidiospores Microscope Slide
"2* 22

FIGURE 18.4 MUSHROOMS ARE MEMBERS OF THE BASIDIOMYCOTA. (A) FRUITING BODIES. (B) BASIDIA WITH BASIDIOSPORES LINING THE GILLS OF MUSHROOMS.

Prepared slide of Pucciniagraminis, uredial stage on wheat

Prepared slides of Pcnicillium and Aspergillus conidio-phores and eonidia

Prepared slides of Rhizopns reproductive structures

Samples of fresh or dried mushrooms, brackct fungi.

puffballs, and stinkhorns

Stained roots containing mycorrhizac

Stalks of wheat infected with Puccinia grawinis

Yeast culture in liquid medium

Procedure for Exercise A

1. Rbizoptts eulture and prepared slides. Using the dissecting microscope, examine the culture of Rhi-zopus. Do not open the lid of the pctri dish. You should be able to sec the sporangiophores, with the spherical sporangia at the tip (sec fig. 18.1). With the compound microscope, examine a prepared slide showing the sporangia and zygospores. You should be able to distinguish these structures as well as the hyphac that make up the colony.

Vcsicular-arbuscular mycorrhizae. Obtain a prc-stained root and place it on a microscope slide. Cover with a drop of the storage fluid and add a coverslip. Examine first under low power and the high power. Look for arbusculcs within the root cells. Draw one of these in the following space.

  1. Yeast culture. Placc a drop of the yeast eulture on a slide. Add a coverslip and examine the slide under the microscope. Find yeast cells that arc budding.
  2. Asomycetc specimens and Peziza prepared slide.

Examine the fruiting bodies that belong to the Division Ascomycota. Your instructor may have several different cup fungi and morels available for you to examine. Each cup, or depression, in the morel is lined with asci. Now examine the prepared slide of Peziza. This is a widely distributed genus that produces a cup-shaped fruiting body. You should be able to find the asci lining the cup, and you should also be able to see 8 ascosporcs within each asens. Why arc there 8 spores? You may need to refer to your textbook to find the answer.

5. Basidiomvcctc specimens. Examine the representatives of the Basidiomvcota that vour instructor has

available in lab. There should be mushrooms, bracket fungi, pullballs. and maybe other types as well.

  1. Infcctcd corn and wheat, and Puccinia prepared slide. Examine the infcctcd plant material. The stalks of wheat are infected with Puccinia grans in is, which causes stem rust of wheat. The corn is infected with Usrilago maydis, which causes corn smut. Roth fungi are also members of the Division Basidiomvcota. Now examine the prepared slide of Pucciniagraminis showing the uredial stage on wheat. Can you distinguish the fungal spore cluster (oillcd a uredium or uredial stage from the host tissue?
  2. Aspergillus and Pénicillium cultures and prepared slides. Aspergillus and Pénicillium arc very common asexual fungi. Although mycologists know that these fungi are members of the Ascomycota, the asexual stage is so common (and the sexual stage is so rare) that we can still consider them asexual fungi. Using the dissccting microscope, examine the cul-turcs of these fungi. Can you see the asexual reproductive structures? Examine the prepared slides of these genera. Can you find the conidiophorcs of these fungi? Draw a conidiophore and several conidia of cach genus in the following space.

Pénicillium

Aspergillus

EXERCISE B: Airborne Fungi

Fungi reproduce by spores, and die majority of fungal spores are dispersed by wind. Fungal spores are therefore a natural component of the atmosphere. In some climates, fungal spores arc present year-round, although thev tend to be most abundant in late summer and fall.

Many people are allergic to ftingal spores both in the atmosphere and indoors. Spore concentrations in the atmosphere can reach levels of up to 200,000 spores per cubic meter of air although this is extreme, and more typical levels from the spring through the tall range between 5,000 and 25,000 spores per cubic meter of air. There arc thousands of different types of spores in the atmosphere. In this exercise, you will perform an experiment to sec how many colonics develop on culture plates exposed at various indoor and outdoor locations.

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