asexual & sexual spores

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REPRODUCTIVE STRUCTURES

ASEXUAL & SEXUAL SPORES

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REPRODUCTION

• Most fungi reproduce Asexually and Sexually by spores

• ASEXUAL reproduction is most common method & produces genetically identical organisms

• Fungi reproduce SEXUALLY when conditions are poor & nutrients scarce

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Spores

• Spores are an adaptation to life on land

• Ensure that the species will disperse to new locations

• Each spore contains a reproductive cell that forms a new organism

• Nonmotile

• Dispersed by wind

Fungi are Spore-ific!!!

• Spores - asexual (product of mitosis) or sexual (product of meiosis) in origin.

• Purpose of Spores – Allows the fungus to

move to new food source.

– Resistant stage - allows fungus to survive periods of adversity.

– Means of introducing new genetic combinations into a population

Reproduce by spores

• Spores may be Formed: – Directly on hyphae – Inside sporangia – On Fruiting bodies

Amanita fruiting body Pilobolus sporangia

Penicillium hyphae

Sporangio-aplanospores

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Hyphal growth from spore

• Mycelia have a huge surface area

• More surface area aids digestion & absorption of food

mycelium

Germinating spore

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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 - in some respects they resemble flagellate protozoa.

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Zoospores

• Because zoospores are motile, the fungi that produce them will require water at some stage during their life cycle.

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Formation of conidia

• Conidia develop by SEPTATION and FRAGMENTATION of a hypha.

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ASexual Reproduction

Asexual Reproduction

Asexually, fungi produce thousands of genetically identical haploid spores, usually on modified cells of the hyphae. When these spores are placed in favourable environmental conditions, they germinate and grow new hyphae, each of which can form a mycelium and produce thousands of new asexual spores

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Three types of Asexual Reproduction

• Fragmentation – part of the mycelium becomes separated & begins a life of its own

• Budding – a small cell forms & gets pinched off as it grows to full size – Used by yeasts

• Asexual spores – production of spores by a single mycelium

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Asexual spores

• Fungi produce two major types of asexual spore:

• Sporangiospores:

• ENDOGENOUS - formed and contained within a SPORANGIUM.

• Formed as a result of the CLEAVAGE OF PROTOPLASM around nuclei. Followed by formation of a wall around each nucleate portion of protoplasm.

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Asexual spores

• Characteristic of fungi belonging to the ZYGOMYCOTA and OOMYCOTA.

• Two main types - ZOOSPORES (motile) and APLANOSPORES (non-motile)

• Conidia:

• EXOGENOUS - often formed at the tip of supporting hyphae called a CONIDIOPHORES

• Characteristic of fungi belonging to the ASCOMYCOTA and BASIDIOMYCOTA.

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ASEXUAL REPRODUCTION

• Fruiting Bodies are modified hyphae that make asexual spores

• An upright stalk called the Sporangiosphore supports the spore case or Sporangium

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ASEXUAL REPRODUCTION

• Types of Fruiting Bodies:

–Basidia

–Sporangia

–Ascus

Basidia

Sporangia

mycelium

Fruiting Bodies

Both are composed of hyphae

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Sexual Reproduction

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SEXUAL REPRODUCTION

• Used when environmental conditions are poor (lack of nutrients, space, moisture…)

• No male or female fungi

• Some fungi show dimorphism

– May grow as MYCELIA or a YEAST –LIKE state (Filament at 25oC & Round at 37oC)

Dimorphic Fungi

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SEXUAL REPRODUCTION

• Haploid 1n hyphae from 2 mating types (+ and -) FUSE (Fertilization)

• Forms a hyphae with 2 nuclei that becomes a ZYGOTE

• The zygote divides to make a SPORE

+ -

SPORE FORMS

Generalized Life Cycle of a Fungus