Introduction to the Fungi and Fungus-Like Organisms
other (dikaryotic), or numerous nuclei in each cell (polykaryotic or multinucleate). The nuclei in a given polykaryotic cell contain the same genetic material (homokaryotic) or the nuclei are genetically different (heterokaryotic). Hyphae of species of “Zygomycota” and the fungus-like Oomycota have few or no septa, contain numerous nuclei, and are called coenocytic hyphae. Some true fungi in basal groups (Chytridiomycota and others) and non-true fungi form zoospores, which are motile mostly due to flagella. The types of flagella are important characteristics by which different fungal and fungus-like groups can be recognized. We use the following terms to distinguish different types of spores (Fig. 2.3). ●●
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opisthokont—a zoospore with one posterior flagellum acrokont—a zoospore with one anterior flagellum isokont—a zoospore with two flagella of similar structure
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anisokont—a zoospore with two flagella of similar structure but of different lengths heterokont—a zoospore with two different flagella pleurokont—a zoospore with lateral insertion of one or several flagella on the cell akont—a spore without flagella. This is the case of most true fungi.
Hyphae grow vegetatively without changing the nuclear phase, producing more hyphae, asexual spores called conidia, yeast cells, or chlamydospores with thick cell walls (Fig. 2.4). The functions of conidia and sexual spores (see below) are multiplication, dispersal, and especially in the case of chlamydospores, long-term survival. Many spores are single celled, but other spores consist of several or numerous cells in different positions. In addition, spores are highly diverse in morphology, size, color, thickness of the walls, and ornamentation, i.e., structures located on the surface of the walls of the spores, like warts or
FIGURE 2.4. Different types of asexual development by a hypha.