Lecture Notes: Fungi and Plant Symbiosis

Fungi Symbiotic Relationships

• Mycorrhizae

  • Mutualistic relationship between plants and fungi.
  • Fungal hyphae absorb nutrients from soil and water for plants.
  • Plants provide sugars from photosynthesis to fungi.
  • Two types:
    • Ectomycorrhizae: Fungal hyphae do not penetrate root cells.
    • Endomycorrhizae (Arbuscular): Fungal hyphae penetrate the root cell walls.
  • Benefits: Efficient nutrient uptake for plants; survival for fungi in the absence of organic matter.
  • Common in 90% of vascular plant species.

• Lichen

  • Association between a fungus and a photosynthetic alga or bacterium.
  • Fungus provides protection; partner provides sugars from photosynthesis.
  • Considered mutualism; allows algae to survive outside aquatic environments.

• Leaf Cutter Ants

  • Ants cultivate fungi by feeding them leaves.
  • Ants consume fungus as a food source.
  • Fungus is domesticated by ants and cannot survive independently.
  • Mutualistic relationship: ants benefit from food, fungus from nutrients and care.

Fungal Pathogens

• Fungi can be pathogens to plants and humans.
• Human fungal infections are challenging to treat due to fungi being eukaryotes.
• Antibiotics are ineffective against fungal infections.

Model Organisms

• Some fungi, like Aspergillus, are used as model organisms.
• Model organisms help in understanding processes applicable to other eukaryotes, including humans.

Introduction to Plants

• Kingdom Plantae

  • Plants are photoautotrophs; energy from sunlight, carbon from CO2.
  • Plants are distinct from red and brown algae.

• Evolutionary Innovations in Plants

  • Green Algae: Early aquatic plants; chlorophytes and charophytes.
  • Land Plants: Transition from water to land involves overcoming various challenges.
  • Benefits of land colonization: less competition, more sunlight, and initially no predators.

Challenges and Solutions for Land Plants

• Need to prevent drying out and transport water/nutrients.

• Support against gravity and facilitate sperm-egg fusion.

• Haplodiplontic Life Cycle

  • Involves multicellular diploid (sporophyte) and haploid (gametophyte) stages.
  • Sporophyte produces spores; gametophyte produces gametes.
  • Cycle includes fusion of gametes to form zygote, developing into sporophyte.

Bryophytes: Earliest Land Plants

• Characteristics

  • Gametophyte is the prominent form.
  • Lack vascular tissue, roots, and true leaves; rely on rhizoids and thalli.
  • Reproduce using structures for male and female gametes.
  • Sperm require water to reach eggs, limiting bryophytes to moist environments.

• Reproduction

  • Eggs and sperm may be on the same or different plants.
  • Dependent on moist environments for sperm motility.

The lecture concludes with a transition to discussing more sophisticated plants in subsequent lectures.