7.4 Classification of fungi
Classification of fungi is based on types of reproduction (either sexual or asexual), and types of hyphae. They are classified as Ascomycota and Basidiomycota. Three major groups i.e., Zygomycota,
7.4.1 Zygomycota (Conjugating Fungi)
Phylum Zygomycota includes fungi in which diploid zygospores are formed examples; are Rhizopus (black bread mold) and Mucor. These are saprobes that generally grow amin complex on remains of plants, bakery products, fruits, and real scale.
It is also utilized vegetables, some are parasites of land protists. In medicine as a source hyphae are aseptate, and possess branching mycelium. The enzyme hyphae are of three types, rhizoid hyphae, stolon hyphae, and sporangiophore hyphae. Asexual reproduction: It takes place by conidia or spores.
Sexual reproduction:
In zygomycetes, it takes place by conjugation. The haploid (n) cells from hyphae of different mating types fuse sexually to produce a zygote, which develops into a zygospore. The plus (+) and minus (-) strains of hyphae produce hormones that stimulate the tip of hyphae to come together forming gametes producing a structure called gametangia.
The plus and minus nuclei fuse to form a diploid nucleus which is the zygote. The zygote develops into a zygospore. The zygospore is thick-walled and resistant to unfavorable conditions.
Germination:
At the return of favorable conditions, the zygospore divides by meiosis. The wall of the zygospore splits and lichen sac originat tonizers of new terrestrial environment hyphae grow upward. The tip of the hyphae develops into a sporangium which has many nuclei. The wall of the sporangium bursts and the spores are released.
Each spore grows into a new plus and minus strain of mycelium."Due to the presence of conjugation and zygospore formation, they are called conjugating Fungi or Zygomycota".
7.4.2 Ascomycota (Sac Fungi)
The name Ascomycota or Sac fungi is given Now most peologit because their spores are produced within sacs called asci (ascus means sac). Ascomycota is the largest group of fungi, containing about 30,000 species. Some examples are with the format.
morels, truffles, yeasts and neurospora. Their hyphae are usually septate. The septa are porous so that cytoplasm can move between compartments. The sac fungi may be unicellular (Yeast) or multicellular (Truffles).
Reproduction:
Ascomycetes reproduce both asexually and sexually. Asexual reproduction:
It takes place either by conidia or budding. The conidium; (Gk: dust) may be unicellular or multicellular, vary in shape and size, and develop on the tips of erected modified hyphae called conidiophores.
There are no sporangia in sac fungi. The colors of conidia vary in different species and they give characteristic brown, blue, pink, or another tint to many of these fungi. Bud is an outgrowth, separates from the parent body, and grows as independent fungi e.g. unicellular yeast (yeast also reproduces asexually by fission).
Sexual reproduction in Ascomycota:
Sexual reproduction occurs by ascospores in both multicellular and unicellular sac fungi.
In sac fungi sexual activities begin when plus and minus strains produce multinucleated sexual bodies. The sexual bodies meet forming a connecting bridge. The nuclei migrate from one body to the next but do not fuse, forming a new dikaryotic hyphae.
The haploid plus and minus nuclei hyphae form a fruiting body known as ascocarp, which develops ascus where spores are produced and released.
In ascus, the dikaryotic hyphae fuse and form a diploid (2n) nucleus, i.e., karyogamy takes place, and the (2n) zygote undergoes meiosis to forms four haploid (n) nuclei, each nucleus then followed by one mitotic division, resulting in eight haploid nuclei later become ascospores. The asci after maturation become swollen, then release the ascospores.
The ascospores are dispersed by wind and if they fall into a suitable location (host), germinate to form new mycelium. e.g., in Neurospora and Saccharomyces (yeast). Morels, Truffles and Penicillium.
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