ASEXUAL REPRODUCTION IN THE ZYGOMYCETES
DECEMBER 4, 2003
I. Purpose: To observe variation in sporangium morphology in the Zygomycetes. Since many of the zygomycetes reproduce asexually more readily than sexually, asexual reproductive structures are used to delimit orders and families. Recent phylogenetic analyses of molecular and morphological data do not support the traditional taxonomic delimitations based on sporangial morphology. To identify species, however, one must be able to recognize the range of sporangial morphological variation. Today you are going on a scavenger hunt for representatives of various sporangia types. You will be given a set of numbered cultures of species of zygomycetes. Using the handout with illustrations of sporangial types for various families you must match each of the cultures with appropriate sporangium morphology. When you think you have identified a sporangial type, provide evidence of your identification to your TA who will check your identifications and give you names of the cultures.
II. Materials: Numbered cultures, 95% ETOH, 2% KOH, 1% aqueous phloxine.
III. Methods: Tough mycelium and easily dislodged and hydrophobic sporangiospores combine to make microscopic observation of these fungi extremely difficult. Always examine plates with the dissecting microscope first, so you can see the overall morphology and habit of sporangia. DO NOT REMOVE THE LIDS FROM PETRI DISHES. OPEN THE LID A SMALL AMOUNT FROM ONE SIDE AND INSERT A STERILE TRANSFER NEEDLE TO REMOVE MATERIAL. Remove small bits of hyphae with sporangia to a glass slide; flood with a drop of 95% ETOH; blot; add equal drops of 2% KOH and 1% aqueous phloxine; blot; add a drop of 2% KOH; add a cover glass. DO NOT DO THIS PROCESS WITH YOUR SLIDE ON THE MICROSCOPE -- IT COULD DAMAGE THE LENSES.
IV. Results: Complete your sporangial worksheet and turn it in to your TA.
SPORANGIAL TYPES
Mucor-type. Multispored sporangium with a well-defined columella. Sporangial wall is frequently short-lived and spores are dispersed by wind. Sporangioles are generally absent.
Mortierella-type. Multispored sporangium with a flat basal septum and no columella. Sporangial wall breaks down to expose spores for wind dispersal.
Pilobolus -type Multispored sporangium with small columella. The sporangium wall remains intact and spores are dispersed as a unit. The sporangium has a basal pad of gelatinous material so the sporangium will stick to plant material and be eaten by herbivores.
Thamnidium – type. Monosporous or multispored sporangiola are borne at the tips of delicate and sometimes intricately branched sporangiophores. In addition, some species also produce large terminal, columellate, and multispored sporangia.
Radiomyces-type Primary sporangiophore terminates in a vesicle from which secondary stalked vesicles arise radially . Unisporous or multisporous sporangioles arise on the secondary vesicles.
Syncephalastrum-type. Multispored merosporangia are produced on the surface of vesicles formed at the tips of simple or branched sporangiophores.
Cunninghamella-type. Monosporous spornagiola are produced on globose vesicles formed at the tips of branched or unbranched sporangiophores.