Structure of Fungi | Do you really know about the structure of fungi
We are going to start from the vegetative structure of fungi and the Hyphal Structure of fungi
Vegetative Structure
Fungi show great variation in the shape and structure of thallus The thallus is usually simple consisting of either single cell or long slender filaments. Accordingly, they can be placed into the following two groups.
1. Unicellular fungi.
In lower groups of fungi, the thallus consists of only a single cell (e.g., Synchytrium). In some other non-mycelial (e.g..fungi called slime molds, the thallus is naked and multinucleated amoeboid mass of protoplasm. Such structure is called plasmodium, e.g., Plasmodiophora, Stemonites, etc.
2. Filamentous fungi.
In the majority of fungi the thallus is made of long and slender filaments called hyphae. The network of hyphae is known as mycelium. The hyphae are hyaline or coloured and may be aseptate or septate. Aseptate hyphae are long, branched and acellular with many nuclei embedded in the common protoplasm. This type of thallus is known as Coenocytic and is characteristic of Phycomycetes; e.g., Mucor.
The hyphae in Ascomycetes, Basidiomycetes And Deuteromycetes (Fungi Imperfecti) are septate. Septa in most cases possessS a central pore (perforated septa) or are non-porous.
In septate hyphae cells are either multinucleate (as in Ascomycetes) or uninucleate (as in Basidiomycetes). The uninucleate hyphae of Basidiomycetes are known as monokaryotic or homokaryotic. Sometimes monokaryotic cells of two different strains or genomes fuse and as a
result each cell of the hyphae may have two nuclei. Such a pair of nuclei is called dikaryon. These nuclei remain together without fusing and divide independently and simultaneously as new cells are formed. Such hyphae are termed as dikaryotic or heterokaryotic.
Modifications of Hyphal Structure
The hyphae of a mycelium are usually distinct. Under certain circumstances, the hyphal structures become modified into some specialized structures. Such modifications are usually adaptations to ecological or physiological factors. Some important modifications are described below.
1. Plectenchyma.
It is loosely or . compactly woven mass of fungal hyphae. Plectenchymá is of the following two types.
(a)Prosenchyma.
In this type of plectenchyma the hyphae lie parallel to one another and are easily distinguishable.
(b) Pseudoparenchyma.
The hyphae lie side by side and in a cross section look like oval or isodiametric parenchyma cells. In this type of tissue the fungal hyphae do not retain their individuality.
2. Sclerotium (plu. = sclerotia).
It is a tough and hard resting body resistant to unfavourable conditions. It may remain dormant for long periods and germinatesS under favourable conditions; e.g., Claviceps.
3. Rhizomorph.
It is a thick, dark coloured strand of somatic hyphae running parallel to each other. The hyphae lose their individuality. The growing tip of the rhizomorph looks like a root tip, hence the name. These structures are resistant to unfavourable conditions and remain dormant until favourable Conditions return. Rhizomorphs also creep under bark of trees or in the soil, thus helping in the spread of fungus, e.g. Armillaria, Agaricus, etc.
Structure of Fungi
At first we know that what is fungi mean what is the definition of fungus and here now we are going to discuss about the structure of fungi so keep reading with us and know about the full structure of fungus or fungi.
Yeast was first described by Antony von Leeuwenhoek in 1680. It is a non-mycelial unicellular fungus. The eukaryotic cells are round, oval or elliptical in shape. Occasionally, the newly
formed cells may adhere to one another in a chain forming a pseudomycelium. The cells are microscopic, generally varying from 5 30u in length and 1 5 u in width. They possess a definite thin cell wall. The cell wall is mainly composed of two polysaccharides glucan (30-40%) and mannan (30%). Besides, proteins (6-8%), lipids (8.5 – 10.5%) and chitin (2%) are also present.
Inner to the cell wall is the cell membrane which surrounds the protoplasm. The cell membrane is characterised by shallow invaginations at certain points. It is made of lipids and proteins. Tc Protoplasm is differentiated into cytoplasm and nucleus. The cytoplasm includes endoplasmic reticulum, ribosomes, mitochondria, golgi apparatus and lipid granules
The mitochondria, besides respiratory enzymes, also contains RNA and DNA. Ribosomes give a granular appearance to the cytoplasm. The centre of the cell is occupied by a large hyaline area consisting of a nucleus and vacuole. There is however, controversy whether the vacuole is a part of the cell nucleus or is a separate entity.
1. Colourless structure in the centre of the cell is the nucleus. According to Wager and Peniston (1910), the hyaline structure situated in the centre of the cell is in fact a vacuolated nucleus. A similar view has been given by Alexopolous (1958). Vacuole is filled with chromatin threads. At one end of the nucleus is present a small nucleolus. Later, Lindgren described the nucleolus as centrosome.
2. Structure situated in the centre of the cell is vacuole. According to Guilliermond (1905) the central hyaline area is a vacuole and the nucleus lies close to it. Nagel (1946) also confirmed this on the basis of staining techniques.
Agar and Douglas (1957) made electron microscopic studies of ultra thin sections of yeast cells. They confirmed that the nucleus is surrounded by a membrane of its own and is distinct from the vacuole. The nuclear envelope is composed of two unit membranes perforated by pores, whereas the vacuole is surrounded by a single unit membrane without pores. The vacuole has many hydrolytic enzymes Such as proteases, ribonucleases and esterases.
Chromosome number of a diploid yeast cell is 8.