Sexual reproduction

Sexual reproduction in fungi has three phases:

(a)Plasmogamy: Two gametes fuse and bring the two haploid tuclei in the same cell.

(b)Karyogamy: The two haploid nuclei fuse to form a single diploid or zygotic nucleus

(c)Meiosis: Reduction division occurs in zygotic nucleus. It Detail of sexual reproduction is different in different fungi:

lsogamy and anisogamy: lsogamy and anisogamy occurs in lower aquatic fungi and some terrestrial higher fungi. These fungi pmcuce motile gametes in gametangia. These gametes fuse to form zygote. The gametes may be isogametes or anisogametes. In anisogametes, smaller gamete is called microgamete and the larger gamete is called macrogamete. The process of union of isogametes is known as isogamy. The union of anisogametes is called anisogamy.

Some–terrestrial fungi also reproduce sexually by direct conjugation of similar gametangia. The product of plasmogamy is zygote. Zygote secrAes thick wall and is changed into a zygospore. Karyogamy occurs in zygospore. Its nucleus undergoes reduction division (meiosis).

Oogamy: In this case, two gametangia are different in size and shape. The smaller is the male gametangium. It is called antheridium. The larger is the female gametangium. It is c died the oogunium. The fungi may be homothallic or heterothallic. In case of hete-othallic the hypae may be + or – strains. The two gainetangia come near each other. The contents of the antheridium are trarderred to the oogonium. These contents are transferred by a pore or by fertilization tube. The contents of the antheridium may be uninucleate or multinucleate. In multinucleate forms only one nucleus left. All other nuclei disintegrate before plasmogarny. The connnts of the oogonium are called egg or oosphere. This type of plasmogamy is called oogamy or heterogamy. .3permatization: In some fungi antheridia are not formed. The fungi develop conidia like spermatia. Spermatia unite with the sex organ or vegetative hyphae of female. Plasmogamy occurs. Thus dikaryotic hyphae are produced. Direct union of vegetative hyphae and parthenogenesis: In some forms plasmogamy takes place by the direct union of monokaryotic vegetative hyphae. Parthenogenesis is also common in fungi.

Plasmogamy and karyogamy

(a) Lower fungi: In the lower fungi karyogamy takes place Immediately after fertilization. The oosphere is transformed into an oospore. Meiosis takes place at the time of oospore germination. In some forms the contents of the antheridium are

transformed into motile male gametes or antherozoies. They move towards the oogonium, enter into it and fertilize the egg

koosphere).

Higher fungi: In the higher fungi karyogamy does not take place immediately after fertilization. The oogonium forms special hyphae. Each cell of this hypha contains two nuclei. Both nuclei divide at the samz time. This type of division is known as conjugate division. Such hyphae are called dikaryotic hyphae. The stimulus of plasinogamy produces fruiting bodies or sporophores. Kaiyogamy takes place in special cells. Meiosis follows karyogamy. It produces special spores.

Clamp connections

These are peculiar structure formed in almost all basidiomycota. The, are formed on the dilcaryotic mycelium usually im terminal hyphae cells during conjugate division of the diWyous. It ensures that the sister nuclei separated into two daughter ea,