Sexual reproduction in Fungi

This video is about sexual reproduction in fungi. Sexual reproduction methods like Gametic copulation, Gamete-Gametangial copulation, Gametangial copulation, Somatic copulation and Spermatization are detailed well. Different sexual spores like ascospores, basidiospores, zygospores and oospores, their formation and properties are explained.

1. SEXUAL REPRODUCTION IN FUNGI Dr C R Meera, M Sc ; Ph D, Assistant Professor Department of Microbiology St Mary’s College, Thrissur-20 Kerala

2. Spores germinate to give rise to new fungi Homothallic   fungus are able to mate with themselves, while in  heterothallic   fungus, opposite sex cells are in different individuals.

3. Sexual Reproduction Fusion of compatible nuclei of two parental cells Sexual reproduction – Plasmogamy , Karyogamy , meiosis Plasmogamy – Fusion of protoplast Karyogamy – Fusion of haploid nuclei of two mating types Meiosis – To reduce the diploid chromosome number to haploid

4. Sex organelles of Fungi Sexually different fungal hyphae are called + and – strain Sex organelles are called Gametangia ( Gematangium ) Gametangium – May differentiate into Gametes Or may contain one or more gamete nuclei Male gametangium is called Antheridium (Antheridia) Female gametangium is called Oogonium ( Oogonia ) Oogonium Antheridium

5. Gametic copulation Gamete- Gametangial copulation Gametangial copulation Somatic copulation Spermatization Sexual Reproduction Methods

6. Gametic copulation - fusion differentiated, uninucleate sexual cells or gametes formed in gametangia to form spores One or both gamates are motile Isogametes- the two members of the fusion pair are alike- Isogamy Heterogametes/ Anisogametes - morphologically different gametes- Heterogamy / Anisogamy 1. Gametic copulation ISOGAMY HETEROGAMY

7. 2. Gamete- Gametangial copulation Two gametangia come into contact, but no fusion between cells Female gametangium contains differentiated female gametes Male nucleus migrates through fertilization tube or pore into female gametangium to form spore

8. 3. Gametangial copulation Male Gametangium Female Gametangium No gametangial differentiation into gametes Two gametangia fuse to give rise to a zygote which develops into a resting spore

9. 4. Somatic copulation Sexual fusion of undifferentiated somatic or vegetative cells No differentiation of hyphae into gametangia

10. 5. Spermatization Union of special male structure called Spermatium (Pl. Spermatia ) with female receptive structure During plasmogamy , spermatia empties its contents into receptive female hyphae

11. Sexual Spores a) Ascospores b) Basidiospores c) Zygospores d) Oospores

12. a) Ascospores Single celled spores in sac like Ascus ( Asci ) 8 Ascospores in each ascus Antheridium and Ascogonium of two mating types fuse to form Ascogenous hyphae, followed by Crozier formation The tip of the crozier then fuses with the penultimate cell and walls itself off from the ascus Ascus – karyogamy – meiosis - 4 Haploid cells- Mitosos - 8 cells Eg : S.cerevisiae , Morels, Neurospora crassa

13. b) Basidiospores Nuclear Fusion Meiosis Vacuole Sterigma Basidiospores Basidium 4 haploid single celled spores on each Basidium Basidium –Club shaped structure formed by fusion of gametangia of two mating types Nuclear fusion and meiosis takes place in the Basidium to form 4 haploid nuclei Basidiospores are produced exogenously at the tips of special outgrowths called Sterigma (Pl. Sterigmata ) Sometimes, mitosis follows meiosis and 8 spores can be seen Eg : Mushrooms, Puff balls, Bracket fungi (inedible mushrooms)

14. c) Zygospores Large thick walled resting spores formed when tips of two sexually compatible hyphae fuse together Zygospores are diploid structures formed by the nuclear fusion of haploid   cells Zygospore remains dormant in adverse environmental conditions When the environment is favorable , the zygospore germinates, meiosis occurs, and haploid vegetative cells are released Eg : Rhizopus , Mucor

15. d) Oospores Formed by gamete – gametangial copulation Formed within special female structure “ Oogonium ” One or more “ Oospheres ” in each oogonium Fertiliztion of Oospheres by male nucleus that migrate through fertilization tube or pore into female gametangium Eg : Saprolegnia

16. Asexual & sexual spores may be surrounded by highly organized protective structures called Fruiting bodies Sexual fruiting bodies- Perithecium and Apothecium Asexual fruiting bodies- Acervulus and Pycnidium Fungal Fruiting bodies