Question

Explain the term sac fungi. Do sac fungi reproduce asexually? Describe the structure of an ascocarp.

Answer 1

Sac fungi constitute the major population of fungi. They have a unique structure on which they are named. This structure is very important for their reproduction as it bears non-motile reproductive structures.

Complete answer:
Sac fungi are also known as Ascomycetes which belong to the phylum Ascomycota in kingdom Fungi and form the subkingdom Dikarya along with Basidiomycota. The sac also known as ascus is the defining feature of these fungi and it contains non-motile reproductive microspores. They are sources of medicinally important compounds like antibiotics and used in fermentation of bread, in breweries. Penicillium is used for antibiotics, Saccharomyces cerevisiae is used in fermentation processes. Some of them are pathogens for animals, plants and humans as well. Serious infections are caused by Aspergillus, Candida and diseases like rice blast, apple scab, powdery mildews and black rot are found in plants which are caused by ascomycetes.

Do sac fungi reproduce asexually?
Ascomycetes are also known as spore shooters as they produce millions of spores inside specialised structures which appear like sac and are known as ascii. Asexual reproduction is a dominant part of their life cycle with the help of which they increase their number and spread their population. Asexual reproduction takes place by conidia formation, conidia are vegetative non-motile haploid spores. Conidia are formed by mitosis because of which they are also known as mitospores and usually have a single nucleus. They originate on the mycelium and are genetically identical to it. They develop in the conidiophores at the specialised ends of hyphae and disperse off from it by the action of wind, water or animals.

Ascomycetes also reproduce by budding which is mostly seen in Saccharomyces cerevisiae. In this process the hyphal tip wall swells up or blows out. Before the formation of a bud, the chitin ring appears at the place of bud formation, this chitin ring provides stability. Cell contents are forced into the newly formed bud which after some time detached from the parent body and develops into a new organism.
Structure of ascocarp:

Ascocarp are the fruiting bodies in ascomycetes which are formed on the hyphae after sexual reproduction. They are in the form of apothecia which are stalked, saucer or cup shaped and having exposed asci, cleistothecium which are spherical and need to rupture in order to release ascospores and perithecia which are globular or flask shaped having apical opening through which ascospores are released.

Note: Sac fungi contain Woronin bodies on which are hexagonal, spherical or oval and present on each side of their septa which separates the hyphal segments and control septal pores. Woronin bodies protect the pores from losing their cytoplasm when the adjoining hypha is ruptured.