Transcript Chapter 31

Chapter 31

Fungi

Intro to Fungi

• • • Eukaryotes Most are multicellular Were once thought to be plants – Recent molecular studies show that they are more closely related to animals than plants

Nutrition

• • Heterotrophs that acquire nutrients by absorption – Small organic molecules are absorbed from surrounding medium Digests food outside of body by secreting enzymes on the food – Exoenzymes: decompose complex molecules into more simple compounds

Nutrition

• • • Saprobes (decomposers) – Absorb nutrients from nonliving organic matter Parasites – Absorb nutrients from living hosts • Some infect lungs of humans • Fungi cause 80% of plant disease Mutualistic symbionts – Absorb nutrients from a host but provide functions beneficial to their partners • Aiding a plant in the uptake of minerals from the soil

Structure

• • Vegetative bodies are usually hidden around and within their food sources Constructed of hyphae – Thin filaments that are composed of tubular walls surrounding plasma membranes and cytoplasm – Form an interwoven mat called mycelium • Feeding network of a fungus • Can be extremely large but hidden because it is subterranean

• • 2000: found the mycelium of one individual fungus in Oregon that is 3.4 miles in diameter and spreads through 2200 acres – Equivalent to over 1600 football fields It is at least 2400 years old and hundreds of ton in weight – One of Earth’s oldest and largest organisms

Structure

• • • Hyphae are divided into cells by cross-walls, or

septa

– Have pores large enough to allow ribosomes, mitochondria, and nuclei to flow from cell to cell Cell walls made of chitin Some don’t have septa – Coenocytic fungi consist of a continuous cytoplasmic mass with hundreds to thousands of nuclei • Resulted from the repeated division of nuclei without cytoplasmic division

Structure

• Parasitic fungi have their hyphae modified as haustoria, which are tips that penetrate the tissues of the host plant – There are even fungi with hyphae that are adapted to feed on animals

Structure – Function Relationship

• Filamentous structure of the mycelium provides an extensive surface area that assists the absorptive function of fungi – Mycelium can grow as much as a kilometer of hyphae each day as it branches out throughout a food source

Reproduction

• Release spores that are produces either sexually or asexually – Amount of spores is tremendous • Puff balls can put out trillions of spores – Spores function as dispersal agents – Airborne spores of fungi have been found more than 100 miles above Earth

Heterokaryotic Stages

• • Nuclei of fungal hyphae and spores are haploid, except for transient diploid stages that form during sexual life cycles Some mycelia become genetically heterogeneous through the fusion of two hyphae that have genetically different nuclei =

heterokaryon

– Different nuclei may stay separate or join in a “crossing over” occasion

Sexy Fungus

• • Plasmogamy: the fusion of the two parents’ cytoplasm when their mycelia come together Karyogamy: fusion of the haploid nuclei contributed by the two parents – These stages may be separated by hours or even centuries – During interim, the hybrid exists as a heterokaryon

Diversity

• • More than 100,000 species are known, and there are estimated 1.5 million species worldwide Fungi are broken down into four phyla: – Chytridiomycota – Zygomycota – Ascomycota – Basidiomycota

Chytridiomycota

• • • • “Chytrids” are mainly aquatic Some are saprobes, others parasitize protists, plants, and animals – Contributing to the worldwide decline of amphibians Form coenocytic hyphae Most primitive of fungi – Diverged earliest in the lineage of fungi

Chytridiomycota

Zygomycota

• • • • • 600 different species Terrestrial and live in soil or on decaying organic matter Mycorrhizae: mutualistic associations with the roots of plants Hyphae are coenocytic Ex: Black Bread Mold

Mycorrhizae

Black Bread Mold

Ascomycota

• • • • • • 60,000 different species “Sac Fungi” Marine, freshwater, and terrestrial Include some of the most devastating plant pathogens Live with algae to form lichens Produce sexual spores in a saclike asci

Ascomycota

Basidiomycota

• • • • 25,000 species – Include mushrooms “Club Fungus” Decomposers of wood and other plant material Long-lived dikaryoric mycelium – Reproduces sexually by producing basidiocarps, which are the source of sexual spores

So…. When you eat mushrooms, you are eating Fungal Genitalia….

“Fairy Rings”

• • A ring of mushrooms Grass in center is stunted because the mycelium is using all the nutrients

Other Categories of Fungi

• • • • Molds Yeasts Lichens Mycorrhizae

Molds

• • • • Rapidly growing, asexually reproducing fungus Saprobes or parasites Mold is a mold if it is in the asexual stage – Later will turn into zygo, asco, or basidiomycotas Imperfect Fungi – Have no sexual stages whatsoever

Yeasts

• • • • Unicellular fungi that inhabit liquid or moist habitats, including plant sap and animal tissues “Bud” to reproduce Raise bread and ferment alcohol – Metabolically active and release small CO2 bubbles or ferment sugars to alcohol pH shift or immunodeficiency can lead to “yeast infections” where normal yeast populations have exponential growth

Yeast

Lichens

• • • Often mistaken for mosses or plants Symbiotic association of millions of photosynthetic microorganisms held in a mesh of fungal hyphae – – Algae provide fungus with food Bacteria in lichens fix nitrogen and provide organic nitrogen – Fungus provides alga with a suitable environment for growth Absorb nutrients from dust in the air or from rain

Lichens

• • • Important pioneers on newly cleared rock and soil surfaces – Burned forests and volcanic flows Lichens make it possible for a succession of plants to grow Can tolerate severe cold and desiccation – Reindeer moss – Can absorb more than ten times their weight in water

Lichens

Mycorrhizae

• • • • • “Fungus Roots” Extensions greatly increase the absorptive surface of the plant roots Exchange minerals accumulated from soil by the fungus for organic nutrients synthesized Occur on almost all vascular plants Show up as mushrooms at the base of trees

Ecological Impact

• • • Principal decomposers – Without them, carbon, nitrogen, and other elements would become ties up in organic matter 10-50% of world’s fruit harvest is lost each year due to fungus During the Revolutionary War, British lost more ships to fungal rot than to enemy attack

Ecological Impact

• Pathogenic: – 30% of fungus is parasitic, mainly on plants – Dutch Elm: Killed ALL American Chestnut trees – Some release toxins that are carcinogenic: Aspergillus – Ergot poisoning: gangrene, nervous spasms, hallucinations • One epidemic killed more than 40,000 people in France in 944 A.D.

– One chemical from ergots is the raw material that LSD is made • Helpful in treating high blood pressure and stopping maternal bleeding after childbirth when given in small doses

Ecological Impact

• • Mycosis: fungal infection – Ringworm – Athletes foot – – Histoplasmosis- causes tuberculosis-like symptoms Opportunistic infections • Only capable of occurring because body is not in homeostasis or the immune response is lowered – Yeast infections Food – Cheeses – – Colas Truffles • Use pigs to locate them because they give off a smell that mimics female pig pheromones

Evolution of Fungi

• • • Oldest fossils of vascular plants have fungus on them – 460 million years ago Fungal ancestors were aquatic flagellated organisms There is compelling evidence that animals and fungi diverged from a common protistan ancestor