General Characteristics and Reproduction of Fungi

General Characteristics of Fungi

• Nutrition: Heterotrophic, absorbing nutrients rather than ingesting. They lack photosynthesis.
• Vegetative State: Typically a non-motile mycelium of hyphae. Motile reproductive stages can occur.
• Cell Wall: Present. Commonly made of glucans and chitin, but sometimes glucans and cellulose (oomycetes).
• Nuclear Status: Eukaryotic, the thallus can have one or multiple nuclei, and can be homo- or heterokaryotic, haploid, dikaryotic, or diploid, with exceptions in certain taxonomic groups. The diploid stage is usually short-lived.
• Life Cycle: Mostly complex, but some are simple.

Reproduction in Fungi

• Sexual Reproduction: Involves nuclear fusion and meiosis.
• Asexual Reproduction: Involves purely mitotic nuclear division. Zoospores (motile), or other types of spores. Sporangiospores, conidia, and budding are common asexual reproduction strategies.
• Propagules: Small spores produced in large numbers.
• Sporocarps: Spore-bearing structures (microscopic or macroscopic).

Beneficial Effects of Fungi

• Decomposition: Nutrient and carbon recycling.
• Biosynthetic Factories: Used in industrial production of alcohol, fats, citric, oxalic, and gluconic acids.
• Antibiotics: Important sources, such as penicillin.
• Model Organisms: Used for biochemical and genetic study, examples include Saccharomyces cerevisiae and recombinant DNA technology.
• Edible Fungi: Some are edible (mushrooms).
• Nutritional Supplements: Yeasts provide vitamins and cofactors.
• Food Flavoring: Penicillium is used to flavor cheeses (Roquefort and Camembert).
• Medical Uses: Ergot produced by Claviceps purpurea contains alkaloids for uterine contractions, blood clotting control, and migraine treatment. Other fungi can be used to control malaria.

Harmful Effects of Fungi

• Destruction: Of food, lumber, paper, and cloth.
• Diseases: Animal and human diseases (including allergies).
• Toxins: Produced by poisonous mushrooms and within food (mycetism and mycotoxicosis).
• Plant Diseases: Affecting crops and plants.
• Spoilage: Damaging agricultural produce like vegetables and cereals.
• Damage to Materials: Damage to materials like magnetic tapes, disks, glass lenses, marble statues, bones, and wax.

Classification of Fungi

• Evolutionary Relationship: Some classify fungi as having evolved from algae due to loss of chlorophyll. However, fungal evolutionary relationships are complex and don't completely align with plants. Other mycologists consider fungi to have a common ancestry with protozoa, placing them in a different kingdom from plants and animals.
• Ainsworth (1971): Treated fungi as a separate kingdom.
• Mycota: Classified into two divisions based on plasmodium and pseudoplasmodium presence: Myxomycota (slime molds) and Eumycota (true fungi). Further subdivided into classes based on sexual reproduction, spore types, etc.
• Myxomycota: Fungal-like members of the kingdom Protozoa; a plasmodium forms the body; multiple nuclei present without a defined cell wall.
• Eumycota: Comprises all fungi with cell walls, organized into classes based on sexual reproduction, spore and mycelium structure.

Mastigomycotina (Oomycetes)

• Thallus: Sac-like or branched thalli are common.
• Mycelium: Hyphae form a mycelium in many species.
• Evolution: Convergent evolution with true fungi.
• Growth: Apical growth is common.
• Specialized Structures/Form: Some examples - appressoria and haustoria
• Cell Structure: Coenocytic hyphae with multiple nuclei, no septa (cross-walls); exception in some cases, especially in old compartments or at the base of reproductive structures.

Zygomycota (Mucorales, Mucoraceae)

• Saprotrophic/Parasitic: Mucorales/Mucoraceae are saprophytic (decomposers) and parasitic fungi.
• Habitat: Found in moist and damp environments, on organic matter like vegetables, fruits, bread, jellies.
• Mycelium: Vegetative structures have branched or coenocytic hyphae.
• Reproduction: Use of sporangiospores and chlamydospores (asexual); and sexual reproduction by zygospores.
• Industrial & Medical Significance: Produce chemicals and alcoholic products. Causes plant diseases and mucormycosis.

Rhizopus

• Mycelium Structure: Three types of hyphae (stolon—aerial, rhizoids—anchoring/digestion, and sporangiophores—reproductive).
• Stolons: These hyphae are aerial, form arches, and touch the substratum to form nodal regions.
• Rhizoids: These branched hyphae anchor the mycelium to the substratum and absorb nutrients.
• Sporangiophores: Reproductive body; form sporangia terminally bearing sporangiospores.
• Asexual Reproduction: Includes the formation of sporangiospores.
• Sexual Reproduction: Zygospores are formed from the fusion of compatible hyphae with the formation of a multinucleated structure and meiosis.

Fungi Classification Summary Diagram

• Kingdom Fungi is divided into two main divisions:
• Myxomycota with 4 classes: (1.Acrasiomycetes, 2.HydroMyxomycetes, 3. Myxomycetes, and 4. Plasmodiophoromycetes)
• Eumycota with 5 subdivisions: (1.Mastigomycotina, 2. Zygomycotina, 3.Ascomycotina 4.Basidiomycotina, and 5.Deuteromycotina)

Additional Details

• Peronosporales (Albuginaceae): Parasite of flowering plants, including white blister diseases.
• Candida albicans: A fungus causing human infections, with characteristics like blastospores, chlamydospores, and pseudohyphae. Relevant diagrams illustrate detailed aspects of its structure.
• Detailed illustrations and diagrams of specific fungal structures and spores provided, with labeled sections like hyphae (septate and coenocytic), sporangiophores, sporangium, rhizoids, stolon. Diagrams also illustrate the life cycle of Rhizopus, including asexual and sexual methods. Further details on the structure/form/function of mycelium/hypha/haustoria.
• Detailed life cycles of specific fungi - important aspects such as the formation of sporangiospores and chlamydospore formations.