Plant Biology: Fungi

Outline

Introduction to Fungi

Importance of Fungi

Biology of Fungi

Fungi Phyla

Symbioses of Fungi

Introduction

Fungi were originally thought of as primitive plants that lack chlorophyll. This, however, is not the case. Fungi are actually more closely related to animals than they are plants.

The only feature shared by fungi and plants is that they are typically sessile.

If something is sessile then it doesn’t move.

There are over 100,000 species of fungi, with 1,200 new species discovered every year.

The largest organism in the world is a fungus, and it spans 2200 acres.

Fungi are principally decomposers.

Fungi can decompose anything, including wood, paint, bread, and fruit. They can also break down lignin and cellulose.

Importance of Fungi

Fungi are the most important causal agents of plant diseases.

Fungi can also cause disease to humans and animals particularly in immunocompromised people and in tropical areas.

Fungi are important to the manufacturing of many food products, including yeasts, cheese, wine, cider, beer, and bread.

They are also a source of chemical compounds, such as the “Wonder Drug” that suppresses immune systems and was used in organ transplants in 1979.

What is a Fungus?

Structure

Fungi are made up of hyphae, fungal filaments.

A mass of hyphae is called mycelium.

Fungi produce spores and can create 1 kilometer of hyphae in 24 hours.

Biology

Fungi are heterotrophic and must consume organic materials.

They do not perform photosynthesis and they store glycogen.

Cell walls in fungi are made up of chitin, distinguishing them from plants.

These cell walls are rigid, so they cannot engulf material. Instead they must digest and absorb it.

Most fungi are saprotrophs.

Saprotrophs are organisms that feed on organic materials from dead organisms.

Many fungi are parasites.

Parasites are organisms that obtain nutrients in a way that harms another organism living in close proximity to it.

Fungi secret enzymes are absorb molecules to digest decomposing matter and can reproduce asexually or sexually, most commonly producing spores.

Fungi Phyla

Fungi are organized into six groups:

1. Microsporidia
2. Chytridiomycota
3. Zygomycetes
4. Glomeromycota
5. Ascomycota
6. Basidiomycota

Microsporidia

Phylum Microsporidia contains 1,300 species.

Microsporidia contains what are considered primitive species of fungi.

They lack many organelles such are mitochondria are are spore-forming, unicellular parasites. They can cause microsporidiosis in immunocompromised humans.

Chytridiomycota

Chytridiomycota contains 710 species known as chytrids.

Many chytrids are saprotrophic, but some are parasitic.

They live in soil, water, and within plants and animals.

Chytrids are very tiny and need water to move, making them mostly aquatic.

Chytrids are known for a frog disease.

Zygomycetes

Zygomycetes include 1,100 species which mostly live on decaying plant and animal matter in soil.

Zygomycetes includes molds, saprotrophic colonizers of humid substrates, that feed on bread, veggies, flowers, dung, plants, and human skin.

Glomeromycota

Glomeromycota includes 170 species and is known primarily for forming endomychorizae with plants in soils all over the world. Nearly 90% of all vascular plants form these symbiotic relationships.

Glomeromycota are obligate symbionts that cannot survive long periods without plant associations.

Ascomycota

Ascomycota is the most species rich group, with 64,000 species.

They are thought to have evolved a billion years ago, take both yeast and filamentous forms, and live in all habitats.

Ascomycota include important plant pathogens.

Basidiomycota

There are 31,500 species in Basidiomycota and they are known as Basidiomycetes

They are very ecologically diverse and are typically saprobes that feed on dead organic matter.

The majority of Basidiomycota are macrofungi that take the forms of mushrooms, toadstools, and puffballs.

Symbioses

Fungi may form symbiotic relationships with other organisms. One such example is the 13,250 lichen forming fungal species.

Lichen

Lichen are mutualistic associations of fungi and algae or cyanobacteria.

Lichen live in the harshest environments on earth including the Arctic and the desert.

They range in size from microscopic to several kilometers, but grow very slowly. Some are over 4,500 years old.

In Antarctica there are 350 lichen species but only 2 plant species.

Lichen can survive harsh environments by rapidly drying to 2-10% water weight and living in suspended animation, enabling them to survive extremes of temperatures and light

Within symbiotic lichen relationships algae contribute carbohydrates and fungi provide substrate and absorbed nutrients.

Lichen potentially formed 600 million years ago, and the organisms cannot live without each other.

Mycorrhiza

The majority of vascular plants form associations with fungi.

Fungi allow for increased water capture and provide essential elements for the plant.

In return, fungi receive carbohydrates.

These associations can create a sort of plant internet from plant to plant so that they may share water and mineral nutrients between each other.

Endomycorrhiza penetrate root cells whereas ectomycorrhiza surround the root cells

Mycorrhiza associations were likely needed for plants to be able to grow on land.