26 Feb FUNGI
“Fungi”
The word “Fungi” (singular Fungus) is derived from latin word FUNGOUR means to flourish, previously used with reference to Mushroom. The fungi are aclorophyllous and heterotrophic thallophytes. They constitute a large and diverse group of plant kingdom. Their resemblance with algae in many respects and therefore, included in the group thallophyta because their plant body consists of a thallus made up of hyphae which together constitute mycelium. In usage meaning of the word has been expanded and includes thallus like, no-green plants such as molds, yeasts and other similar organisms closely related to mushrooms . Thus, the fungi are a large group of simple thallus like plants, lacking chlorophyll.
Habitat of Fungi
The fungi are most diversified in their habitat. They are found in almost all possible types of habitats in the earth, where organic material either living or dead is present . Thus they are universal or cosmopolitan in distribution. Most of the fungi are terrestrial, occurs in soil, rich in dead and decaying organic materials. The terrestrial fungi thrive best in humus soil. Some other species are aquatic found in the water and are called the aquatic fungi.
Plant Body
The plant body or vegetative phase of fungi is represented by thallus. It may be unicellular or multicellular filamentous.
Unicellular Thallus
In lower fungi especially in unicellular structure more or less spherical in shape. It performs both the phases of life within a single cell. After maturation or completion of vegetative phase it performs the sexual phase such fungi are known as holocarpic fungi, but both the phases of life cycle do not occur together in same thallus (Synchytrium). In this case mycelium is completely absent.
Contrary to this, in Plasmodiophora, a naked multinucleate, amoeboid mass of protoplast represents the vegetative phase and is termed plasmodium. The protoplast of diploid plasmodium divide to form resting spores, these spores further forms vegetative phase. Similarly Yeasts also have a unicellular thallus but sometimes cells remain attached in chains forming a pseudomycelium and thus related to filamentous forms.
Filamentous Thallus:
The plant body of most of the fungi is branched and filamentous hyphae or filamentous thallus which forms a net like structure known as mycelium except some unicellular fungi. The mycelium originates through germination of spores. Germination of spores takes place after getting suitable substratum where conditions for life are favourable. When the spore after germination produces only a short, tubular structure of limited growth it forms to a net like interwoven cottony mass of fine branched filaments. The long, fine structures or filaments are called as hyphae.
Types of Mycelium:
The fungal mycelium is a simple multinucleate structure lacking completely the internal boundaries. The hyphae may be segmented or non- segmented. The segment hyphae possess cross walls in them at regular intervals called septa. The mycelium having septa called septate while the hyphae without cross walls are known as aseptate ones . On the basis of presence or absence of internal septa, the fungal mycelium may be divided into two categories.
(i) Aseptate Mycelium:
In the lower fungi or algal fungi the Phycomycetes the plant body in the vegetative phase usually lacks internal partitions of any kind, although it bear multinucleus. Thus the hyphae are aseptate and multinucleate. It grows terminally through apical parts of the hyphae and simultaneously accompanied by increase in the number of nuclei by nuclear divisions.
(ii) Septate Mycelium:
Phycomycetes, lacks septa in their hyphae while other higher fungi i.e. Ascomycetes and Basidiomycetes, they develop internal cross walls in the mycelium called septa hence the hyphae divide into segments. These segments nay be uninucleate or multinucleate and appear at regular intervals behind the tip of hyphae. Generally the septa in a septate mycelium are transverse while oblique or longitudinal septa are rarely appeared.
ASCOMYCOTINA
Various types of morphology appear in their members, as unicellular form like yeast and multicellular profusely branched and septated mycelium. This group is distinguished from other fungi by the development of ascospores and also by conidial stage. Vegetative reproduction takes place by fission, fragmentation, and budding and it is the most common methods in unicellular form, members reproduce asexually by the non motile spores such as oidia, chlamydospores and conidia. Conidia developed in conidiophores when the spores are borne free i.e. not contained within membrane the sporophore is referred to as conidiophores.
(i) Saccharomyces (Yeast)
It produces two types of enzymes: an extracellular invertase and an intracellular zymase. The invertase hydrolyses cane sugar to dextrose or invert sugar and zymase breaks invert sugar into ethyl alcohol and carbon dioxide. They easily destroy soft cheese and similar foods, for they impart repulsive yeasty flavor.
(ii) Aspergillus
Aspergillus is a saprophytic fungus, represented by 132 species occurring over a wide range of habitats. Some species of aspergillus are found as parasites on plants, causing crown rot of groundnut and boll rot of cotton. A. flavous contaminates groundnut and other dry food stuffs. It produces some toxic substances called aflatoxins, which are carcinogenic.
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