fungal spores 2010

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Assignment on Classification and importance of fungal sporesSubmitted to Dr. Abhishek Submitted by Ajay Rai (4929)

DIVISION OF BACTERIOLOGY AND MYCOLOGY INDIAN VETERINARY RESEARCH INSTITUTE IZATNAGAR 243 122.

OUTLINE Introduction Classification of spore Classification of Asexual spore Classification of Sexual spore Importance

INTRODUCTION Spore formation is one of method of reproduction in fungi. Spores are generally more environmental conditions. resistant to adverse

Spores represent microscopic dispersal (sporangiospores and conidia) or dormant (oospores and Zygospore) survival propagules produced by most species of fungi.

Fungal spores may be unicellular or multicellular e.g. conidia produced by Alternaria species are multicellular. Some spores possess a textured or ornamented surface e.g. uredospores of Melampsora epita.

CLASSIFICATIONThere are two types of spore formed in fungi(1)Asexual spore (2)Sexual spore (1)Asexual spore Sporangiospores Conidia (2)Sexual spore Ascospore Basidiospore Zygospore Oospore

Asexual sporesAsexual spores may be divided into two broad categories(1) Sporangiospore (2) Conidia (1) (2) Sporangiospore zoospores (motile) & Aplanospore (non-motile) Conidia Thallic conidia Blastic conidia

(1) Sporangiospores: If the spores develop within a sac (sporangium, Pl. sporangia) at a hyphal tip, they are called sporangiospores. A sporangium is a sac-like structure whose entire contents are converted through cleavage into one or more, usually many spores. Endogenously formed Formed as a result of the cleavage of protoplasm around nuclei.

Followed in some cases by formation of a wall around each nucleate portion of protoplasm. Characteristic of fungi belonging to the chytridiomycota, oomycota and hyphochytridiomycota. Two main types ZOOSPORES (motile) and APLANOSPORES (non-motile)

(i) Aplanospore : Nacked, thin walled, single celled uni or multinucleate, nonmotile spores It can be of different shape and size.

(ii) Zoospores: Zoospores are motile sporangiospores and the sporangia in which they form are called zoosporangia. The protoplasm of zoospores is not surrounded by a wall that's why in some aspects they resemble flagellate protozoa. Because zoospores are motile, the fungi that produce them will require water at some stage during their life cycle.

Zoospores may be uniflagellate or biflagellate(a) Uniflagellate zoospore -flagellum are mostly posteriorly placed except in few where it is at anterior end. (b) Biflagellate zoospore posterior. one flagellum anterior and other

--Usually anterior placed flagellum has fine haires and is called Tinsel flagellum . Fine haires are called Flimmer or Mastigonems .

-- Posterior flagellum consist of long, relatively thick rod which narrows abruptly at its tip to a delicate prolongation of variable length known as whiplash flagellum

Three different types of zoospore distinguish Chytridiomycota, Hyphochytridiomycota and Oomycota.

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(2) Conidia If spores are not enclosed in a sac but produced at tips or sides of hyphae they are termed conidia (sing. Conidium). Exogenous - often formed at the tip of supporting hyphae called a Conidiophores . Develop in a variety of ways. Characteristic of MITOSPORIC FUNGI and fungi belonging to the ASCOMYCOTA and BASIDIOMYCOTA.

Two main types - Thallic and Blastic conidia

(I) Thallic Conidia develop by septation and fragmentation of a hypha. may develop at the tip of a hypha or in an intercalary (central) position. in both cases, all layers of the hyphal wall are involved in spore formation.

(a) Arthrospores (Oidia) : Formed by septation and fragmentation of an existing hypha. Elements of the hypha (incl. all wall layers) become converted into conidia. Each fragment is rounded off and liberated in succession. Separation of the conidia from one another is due to breakdown of the middle region of each septum.

(b) Chlamydospores : A type of resting or survival spore. Found in several groups of fungi (e.g. Zygomycota and mitosporic fungi). An intercalary (see diagram) or apical hyphal cell or compartment enlarges, rounds up and develops a thickened, often pigmented wall.

Contain dense cytoplasm and nutrient storage compounds. Thick-walled (All wall layers are involved in their formation). Become isolated from adjacent hyphal compartment(s) by the sealing of septal pores (if present). Usually develop under conditions of stress that are unfavourable for normal somatic growth.

(ii) Blastic Conidia Develop by a BUDDING or SWELLING PROCESS. May develop as SINGLE SPORES or in succession to form a CHAIN OF SPORES. (a) Blastospores: Formed by budding of a hypha or yeast cell. Both wall layers are involved. The spore may remain attached and bud further blastospores giving rise to a branched chain of spores.

(b) Porospores: The developing spore emerges through a distinct 'pore' in the hyphal wall. Only the inner layer of the hyphal wall is involved in spore development. The new spore then develops its own new inner wall layer. The outer spore wall is often thickened and pigmented. A scar is usually obvious at the point of detachment from the hypha (conidiospore).

(c) Aleuriospores : Develop as single, terminal spore. Conidiophore apex inflates and becomes separated by a septum at an early stage in spore development. Both wall layers are involved in spore formation . The spore possesses a wide, truncate scar. Normally no further development of spores occurs at the point of detachment. So the next spore usually has to develop by production of a branch below the scar on the conidiophore.

(d) Annellospores : In some species that form conidia in a manner similar to that described for aleuriospores (before) a new growing point does develop at the scar. A chain of spores may develop. The conidiophore gets a little longer with each spore produced. Annellations (ring-like scars) are observed around this elongating portion. Each annellation represents the production of one annellospore.

(e) Phialospores: Form in succession . Each spore is pushed up from the tip of the conidiophore, which is now called a PHIALIDE. The spore wall is new and distinct from both wall layers of the phialide. The first spore has a cap, which represents the tip of the phialide wall through which the spore emerged - all other spores in the chain are smoothly rounded.

Sexual spores (1) (2) (3) (4) Sexual reproduction in most of the fungi involves the formation of specialized spores. There are four types of sexual spores are describedAscospore Basidiospore Zygospore Oospore

(1) Ascospore: Fusion of male and female gamete results in the formation of egg, which through successive divisions, generate spores. If the spores remain in the egg, which is then called as ascus, they are referred to as ASCOSPORES

.

Produce one to eight ascospores in a single, round ascus.

Simplest representative of this class is SACCHROMYCES.

Majority of ascomycetes develop septate mycelia with several club-shaped ascospores enclosed in a fruiting body called ASCOCARP . ---Completely closed ascocarp-CLEISTOTHECIUM ---Saucer or cup-shaped ascocarp that is completely opened at maturity- APOTHECIUM ---spherical or flask shaped ascocarp with a pore opening PERITHECIUM.

(2) Basidiospore: Develop in club-shaped structure called basidium (Pl. basidia) Basidium is a structure bearing on its surface a definite number of basidiospores (typically four) that usually are formed following karyogamy and meiosis.

Characteristic of class basidiomycetes which includes mushrooms, toadstools and bracket fungi.

(3) Zygospore

(thick walled resting spore) When the tip of neighbouring hyphae join and the contents fuse with the pairing of nuclei, a new cell develops with thick, pigmented, rough walls. This structure is called Zygospore.

This pattern of reproduction is common to mucor, absidia and Rhizopus of class zygomycetes and the order mucorales.

(4) Oospore (thick walled resting spore) A thick-walled spore that develops from an oosphere through either fertilization or parthenogenesis. Oosphere is a large , naked, nonmotile female gamete. Zygospore and Oospore both are thick walled resting spores but difference is that Zygospore is resulting from the fusion of two similar gametes and Oospore is developed as a result of two unlike cells.

Importance of SporesA. Biological: 1) Allows for dissemination 2) Allows for reproduction 3) Allows the fungus to move to new food source. 4) Allows fungus to survive periods of adversity. 5) Means of introducing new genetic combinations into a population. Practical

B. Practical: 1) Rapid identification (also helps with classification). 2) Source of inocula for human infection. 3) Source of inocula for contamination

C. Commercial: Fungal spores possess a wide range of CONSTITUTIVE ENZYMES. These enzymes increase in metabolic activity that accompanies germination, has resulted in spores being used as biological catalysts in a number of commercial CHEMICAL TRANSFORMATION processes.

Examples: The transformation of penicillins by spores of Fusarium moniliforme. The conversion of fatty acids to methylketones by spores of Penicillium roquefortii.

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