C2.6 - Kingdom Fungi

Overview, Structure, and Function

• Heterotrophic decomposers
• Consist of hyphae
• hyphae: tightly-packed filaments
  • have cross-walls (most fungi)
  • cross-walls: additional cell walls that divide long filaments into many separate end-to-end cells
• mycelium: interwoven hyphae mass
• fruiting body: reproductive structure
  • usually visible part of fungi appearing above ground
• Surface to volume area of hyphae and substrate very high allowing maximum absorption
• Cell walls composed of chitin

Structure of fungi

Diversity and Importance of Fungi

• fungi are more closely related to animals than plants
• they are heterotrophic and absorb nutrients from the environment
• use enzymes to break down organic matter outside their bodies
• require oxygen to survive
• include mushrooms, moulds, yeast, truffles, rusts
• over 100,000 known species with wide diversity
• important decomposers recycling carbon and nitrogen
• help plants by recycling nutrients and forming symbiotic relationships
• some fungi are parasites that harm plants and animals
  • cause many plant diseases and human infections like ringworm and athlete’s foot

Division Zygomycata

• Key characteristics: Common terrestrial moulds
• Common terrestrial moulds
• Live on decaying plant and animal matter
• Some are plant parasites
• Capable of sexual and asexual reprod.
• i.e. Rhizopus stolonifer, black bread mould

Division Ascomycota

• Key characteristics: sacs called asci that contain sexual spores
• Diverse group incl.
  • moulds
  • plant parasites like
    • powdery mildew
    • Dutch elm disease
  • ergot
  • yeasts
  • morels
  • truffles
• Terrestrial and aquatic
• Capable of sexual and asexual reprod.

Examples

Powdered mildew

Morel mushroom

Truffle mushrooms

Division Basidiomycota

• Key characteristics: club-shaped cell called a basidium that produces sexual spores
• Mushrooms, toadstools, puffballs, rusts and smuts
• Grow spore-producing bodies called basidia
• Sexual reproduction only

Examples

Giant puffball

Orange rust fungus

Corn smut

Mycorrhizae

• mychorrhizae: fungi that form symbiotic relationships with plant roots
• Help plant to absorb nutrients like phosphorous and trace minerals
• Act like extension of plant roots
• Fraction of diameter of plant root
  • can penetrate into places where plants cannot
• Plant provides food to fungi
• Plant typically grows poorly in sterile environments

Diagram of mycorrhizae

Lichens

• Mutualistic, symbiotic association between fungi and green algae
• Algae provide food for symbiont
• Fungi provide protection, structure and mineral nutrients
• Inhabit harsh environments but sensitive to pollution

Examples

Crustose (Encrusted) Lichens

Foliose (Leafy) Lichens

Fruticose (Shrubby) Lichens

Chytridomycota

• chytridomycota: fungi w/ flagellated spores
• chytrids

Reproduction

Asexual

• piece of hyphae breaks off and releases spores
• spore: haploid cell that help fungi reproduce
  • spread by wind and can withstand unfavourable conditions for long time
  • capable of germinating and producing hyphae or yeasts in favourable conds.

Sexual

• 2 different sexes in fungi: + and -
• opposite haploid hyphae grow toward each other and fuse to form diploid zygospore
  • 1 chromosome from each parent “hyphae”
• Club and sac fungi (i.e. mushrooms, puffballs, morels)
  • joining of two genetically diff. hyphae produces dikaryotic hyphae
  • dikaryotic: containing two nuclei per cell
    • one from each “parent” hyphae
  • eventually, dikaryotic nuclei fuse and form single diploid nucleus
  • diploid nucleus then divides into haploid spores (cycle repeats)

Reproduction of black bread mould (R. stolonifer)

Climate Change

• rising temperatures are shifting plant ranges north
• plants migrate faster than soil organisms like fungi and insects
• new soil conditions may not support plant-fungi symbiosis
• disrupted symbiosis can reduce plant success
• air pollution has destroyed half of western Europe’s mycorrhizae
• loss of fungal webs could impact entire soil ecosystems