Fungi are eukaryotic, spore bearing, achlorophyllous, heterotrophic organisms that generally reproduce sexually and asexually and whose filamentous, branched somatic structures are typically surrounded by cell walls containing chitin or cellulose or both with many organic molecules and exhibiting absorptive nutrition.
Structure of Fungi
Fungal Thallus / Soma
It is a vegetative or fungal body. Thalli is the plural of the thallus. The Fungal thallus have no chlorophyl at all, and not differentiation into stem, roots, and leaves also lacking the vascular system which differentiates it from plants.
Hypha
The hypha is a thin, transparent, tubular filament filled with protoplasm. It is the unit of a filamentous thallus and grows by apical elongation. Hypha means the web.
Mycelium
Mycelium is a network of hyphae. This network constituting the filamentous thallus of a fungus. Its color depends upon the presence of the pigments in the cell wall. If there is no pigment then it may be colorless. The mycelium may be ectophytic or endophytic.
Types of Fungal Thalli
- Plasmodium
- Unicellular thallus
- Filamentous or multicellular thallus
Plasmodium
Plasmodium is the mass of multi nucleated protoplasm, which is naked and feeding in amoeboid fashion. Eg. Plasmodiophora brassicae.
Unicellular Thallus
As the name suggest, it is consist of the single celll. Eg.Chytrids, Synchytrium
Filamentous or Multicellular thallus
Majority of fungi i.e., true fungi are filamentous, consisting of a number of branches, a thread like filaments called hyphae. Eg. Many fungi, Alternaria.
Fungi based on reproductive structures:
Holocarpic (holos=whole+karpos=fruit): In this whole thallus is converted into 1 or more reproductive structures, that thallus is called holocarpic thallus. Synchytrium
Eucarpic (Eu=good+karpos=fruit): If the thallus is differentiated into two parts in which one part a vegetative part absorbs nutrients and a reproductive part forms reproductive structures, such a thallus is called Eucarpic thallus. Pythium
Ectophytic fungus: If the thallus is present on the body surface of the host then it is called ectophytic. Eg. Oidium.
Endophytic fungus: If the fungus not present on the body surface but, penetrates into the body of host cell then it is called endophytic. Eg. Puccinia Endophytic fungus may be inter cellular (hypha grows in between the cells), or intra cellular (hypha penetrates into the host cell).Eg.Ustilago, or vascular (xylem vessels) Eg. Fusarium oxysporum.
In the inter cellular fungus penetrate the host cell with the help of a special organs called Haustoria. Haustoria are absent in the intracellular. Endophytic intra cellular mycelium absorbs food directly from protoplasm with out any specialized structures.
In ectophytic mycelium, haustoria are produced in epidermal cells.
Septation in Fungi
Fungal hyphae having partitions. Fungus is divided into a number of compartments. These walls are called septa. A hypha with septate is called septate hypha or coenocytic hypha. A hypha without septa is called aseptate or non-septate or coenocytic hypha. the nuclei are embedded in the cytoplasm. Eg. lower fungi like Oomycetes and Zygomycetes.
General types of septa
Types of Septa based on their formation
Primary septa: Primary septa are formed in direct association with nuclear division (mitotic or meiotic) and are laid down between daughter nuclei separating the nuclei /cells. Eg. Higher fungi like Ascomycotina and Basidiomycotina.
Adventitious septa: The Adventitious are formed independent of nuclear division and these are produced to delimit the reproductive structures. Eg. lower fungi like Oomycetes and Zygomycetes in which septa are produced below gametangia (sex organs) which separate them from rest of the cells.
Types of Septa Based on construction:
a) Simple septa: As the name suggests, it is the most common type of septa, it is a plate like, with or without perforation.
b) Complex septa: This this type a barrel shaped swelling of septal wall surrounded the septum and covered on both sides by a perforated membrane termed the septal pore cap or parenthesome. Eg. Dolipore septum in Basidiomycotina.
Types of Septa Based on perforation:
a) Complete septa: In this type of A Septum is a solid plate with not a pore or perforations.
Eg. Adventitious septa in lower fungi.
b) Incomplete septa: In this, A septum contains a central pore.