31 fungi text

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 31Chapter 31

Fungi


• Overview: Mighty Mushrooms

• Fungi

– Are diverse and widespread

– Are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients

Figure 31.1


• Concept 31.1: Fungi are heterotrophs that feed by absorption

• Despite their diversity

– Fungi share some key traits


Nutrition and Fungal Lifestyles

• Fungi are heterotrophs

– But do not ingest their food

• Fungi secrete into their surroundings exoenzymes that break down complex molecules

– And then absorb the remaining smaller compounds


• Fungi exhibit diverse lifestyles

– Decomposers

– Parasites

– Mutualistic symbionts


Body Structure

• The morphology of multicellular fungi

– Enhances their ability to absorb nutrients from their surroundings

Hyphae. The mushroom and its

subterranean mycelium are a continuous

network of hyphae.

Reproductive structure.

The mushroom produces

tiny cells called spores.

Spore-producing

structures

20 m

Mycelium

Figure 31.2


• Fungi consist of

– Mycelia, networks of branched hyphae adapted for absorption

• Most fungi

– Have cell walls made of chitin


• Some fungi

– Have hyphae divided into cells by septa, with pores allowing cell-to-cell movement of materials

• Coenocytic fungi

– Lack septa

Nuclei

Cell wall

Septum

Pore

(a) Septate hypha (b) Coenocytic hypha

Cell wall

Nuclei

Figure 31.3a, b


• Some unique fungi

– Have specialized hyphae that allow them to penetrate the tissues of their host

Nematode Hyphae 25 m

(a) Hyphae adapted for trapping and killing prey

(b) Haustoria

Fungal hypha Plant cell wall

Haustorium

Plant cell plasma membrane

Plant cell

Figure 31.4a, b


• Mycorrhizae

– Are mutually beneficial relationships between fungi and plant roots


• Concept 31.2: Fungi produce spores through sexual or asexual life cycles

• Fungi propagate themselves

– By producing vast numbers of spores, either sexually or asexually


• The generalized life cycle of fungi

Key

Haploid (n)

Heterokaryotic(unfused nuclei fromdifferent parents)

Diploid (2n)

PLASMOGAMY(fusion of cytoplasm)

Heterokaryoticstage

KARYOGAMY(fusion of nuclei)

SEXUALREPRODUCTION

Spore-producingstructures

SporesASEXUALREPRODUCTION

Zygote

Mycelium

GERMINATION GERMINATION

MEIOSIS

Spore-producingstructures

SporesFigure 31.5


Sexual Reproduction

• The sexual life cycle involves

– Cell fusion, plasmogamy

– Nuclear fusion, karyogamy

• An intervening heterokaryotic stage

– Occurs between plasmogamy and karyogamy in which cells have haploid nuclei from two parents


• The diploid phase following karyogamy

– Is short-lived and undergoes meiosis, producing haploid spores


Asexual Reproduction

• Many fungi can reproduce asexually


• Many fungi that can reproduce asexually

– Grow as mold, sometimes on fruit, bread, and other foods

2.5 m

Figure 31.6


• Other asexual fungi are yeasts

– That inhabit moist environments

– Which produce by simple cell division10 m

Parent cell

Bud

Figure 31.7


• Many molds and yeasts have no known sexual stage

– Mycologists have traditionally called these deuteromycetes, or imperfect fungi


• Concept 31.3: Fungi descended from an aquatic, single-celled, flagellated protist

• Systematists now recognize Fungi and Animalia as sister kingdoms

– Because fungi and animals are more closely related to each other than they are to plants or other eukaryotes


The Origin of Fungi

• Molecular evidence

– Supports the hypothesis that fungi and animals diverged from a common ancestor that was unicellular and bore flagella

• Fungi probably evolved

– Before the colonization of land by multicellular organisms


• The oldest undisputed fossils of fungi

– Are only about 460 million years old

50 m

Figure 31.8


The Move to Land

• Fungi were among the earliest colonizers of land

– Probably as symbionts with early land plants


• Concept 31.4: Fungi have radiated into a diverse set of lineages

• The phylogeny of fungi

– Is currently the subject of much research

• Molecular analysis

– Has helped clarify the evolutionary relationships between fungal groups, although there are still areas of uncertainty


• The phylogeny of fungi

ChytridsZygote

fungiArbuscular mycorrhizal

fungi

Sac fungi

Club fungi

Ch

ytrid

iom

yco

ta

Zyg

om

yco

ta

Glo

me

rom

yco

ta

Asc

om

yco

ta

Ba

sid

iom

yco

taFigure 31.9


• A review of fungal phyla

Table 31.1


Chytrids

• Fungi classified in the phylum Chytridiomycota, or chytrids

– Are found in freshwater and terrestrial habitats

– Can be saprobic or parasitic


• Chytrids are unique among fungi

– In having flagellated spores, called zoospores

25 m

4 m

Hyphae

Flagellum

Figure 31.10


• Until recently, systematists thought that

– Fungi lost flagella only once in their history

• Molecular data

– Indicate that some “chytrids” are actually more closely related to another fungal group, the zygomycetes

Some

chytrids

Zygomycetes and other chytrids

Glomeromycetes,

ascomycetes, and

basidiomycetes

Common ancestor

Key

Loss of

flagella

Figure 31.11


Zygomycetes

• Fungi in the phylum Zygomycota, the zygomycetes

– Exhibit a considerable diversity of life histories

– Include fast-growing molds, parasites, and commensal symbionts

– Are named for their sexually produced zygosporangia


Rhizopus

growing

on bread

ASEXUAL

REPRODUCTION

Mycelium

Dispersal and

germination

MEIOSIS

KARYOGAMY

PLASMOGAMY

Key

Haploid (n)

Heterokaryotic (n + n)

Diploid

Sporangium

Diploid

nuclei

Zygosporangium

(heterokaryotic)

100 m

Young

zygosporangium

(heterokaryotic)SEXUAL

REPRODUCTION

Dispersal and

germination

Mating

type (+)Mating

type ()

Gametangia with

haploid nuclei

50 m

Sporangia

• The life cycle of Rhizopus stolonifer

– Is fairly typical of zygomycetes Mycelia have

various mating types

(here designated +,

with red nuclei, and ,

with blue nuclei).

1

Neighboring mycelia of different

mating types form hyphal extensions

called gametangia, each walled off

around several haploid nuclei by a septum.

2

A heterokaryotic

zygosporangium

forms, containing

multiple haploid

nuclei from the two

parents.

3

The sporangium

disperses genetically

diverse, haploid spores.

7

4 This cell develops a

rough, thick-walled

coating that can resist

dry environments and

other harsh conditions

for months.

5 When conditions are favourable,

karyogamy occurs, followed by

meiosis.6 The zygosporangium

then breaks dormancy,

germinating into a

short sporangium.

The spores

germinate and

grow into new

mycelia.

8

9 Mycelia can also reproduce

asexually by forming sporangia

that produce genetically identical haploid spores.

Figure 31.12


• Some zygomycetes, such as Pilobolus

– Can actually “aim” their sporangia toward conditions associated with good food sources

0.5 mmFigure 31.13


• Zygosporangia, which are resistant to freezing and drying

– Are capable of persisting through unfavorable conditions

– Can undergo meiosis when conditions improve


Microsporidia

• Microsporidia

– Are unicellular parasites of animals and protists

– Are now classified as zygomycetes10

m

Host cell nucleus

Developing microsporidian

Spore

Figure 31.14


Glomeromycetes

• Fungi assigned to the phylum Glomeromycota

– Were once considered zygomycetes

– Are now classified in a separate clade


• All glomeromycetes

– Form a distinct type of endomycorrhizae called arbuscular mycorrhizae

2.5 m

Figure 31.15


Ascomycetes

• Fungi in the phylum Ascomycota

– Are found in a variety of marine, freshwater, and terrestrial habitats

– Are defined by the production of sexual spores in saclike asci, which are usually contained in fruiting bodies called ascocarps


• Ascomycetes

– Vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels

(a) The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia give this species its common name: orange peel fungus.

(b) The edible ascocarp of Morchella esculenta, the succulent morel, is often found under trees in orchards.

(c) Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open.

(d) Neurospora crassa feeds asa mold on bread and other food (SEM).

10 m

Figure 31.16a–d


• Ascomycetes reproduce

– Asexually by producing enormous numbers of asexual spores called conidia


• The life cycle of Neurospora crassa, an ascomycete

Dispersal

ASEXUALREPRODUCTION

Germination

Mycelium

Conidiophore

Germination

Dispersal

Mycelia

AsciEightascospores

Ascocarp

Fourhaploidnuclei

MEIOSIS

KARYOGAMY

PLASMOGAMY

SEXUALREPRODUCTION

Diploid nucleus(zygote)

Ascogonium Ascus(dikaryotic)

Dikaryotichyphae

Matingtype ()

Conidia;mating type ()

Key

Haploid (n)

Dikaryotic (n n)

Diploid (2n)

Ascomycete mycelia can also reproduce asexually by producing haploid conidia.

7 Neurospora can reproduce sexually by producing specialized hyphae. Conidia of the opposite mating type fuse to these hyphae.

1

A dikaryotic ascus develops.2

Karyogamy occurs within theascus, producing adiploid nucleus.

3

The diploid nucleusdivides by meiosis, yieldingfour haploid nuclei.

4

The developing asci are contained in an

ascocarp. The ascospores are discharged forciblyfrom the asci through anopening in the ascocarp. Germinating ascosporesgive rise to new mycelia.

6

5 Each haploid nucleus dividesonce by mitosis, yielding eightnuclei. Cell walls develop aroundthe nuclei, forming ascospores (LM).Figure 31.17


Basidiomycetes

• Fungi in the phylum Basidiomycota

– Include mushrooms and shelf fungi

– Are defined by a clublike structure called a basidium, a transient diploid stage in the life cycle


• Basidiomycetes

(a) Fly agaric (Amanita muscaria), acommon species in conifer forests in the northern hemisphere

(b) Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat

(c) Shelf fungi, important decomposers of wood

(d) Puffballs emitting spores

Figure 31.18a–d


• The life cycle of a basidiomycete

– Usually includes a long-lived dikaryotic mycelium, which can erect its fruiting structure, a mushroom, in just a few hours

Figure 31.19


PLASMOGAMY Dikaryoticmycelium

Basidiocarp(dikaryotic)

KARYOGAMY

Key

MEIOSIS

Gills linedwith basidiaSEXUAL

REPRODUCTION

Matingtype ()

Matingtype ()

Haploidmycelia

Dispersalandgermination

Basidiospores

Basidium withfour appendages

Basidium containingfour haploid nuclei

Basidia(dikaryotic)

Diploidnuclei

Basidiospore1 m

Basidium

Haploid (n)

Dikaryotic (n n)

Diploid (2n)

• The life cycle of a mushroom-forming basidiomycete

Each diploid nucleus yields four haploid nuclei. Each basidiumgrows four appendages, and one haploid nucleusenters each appendage and develops into a basidiospore (SEM).

6

Two haploid mycelia of different mating typesundergo plasmogamy.

1 A dikaryotic mycelium forms, growing faster then, and ultimately crowding out, the haploid parental mycelia.

2

3 Environmental cues such as rain ortemperature changes induce the dikaryoticmycelium to formcompact masses thatdevelop intobasidiocarps(mushrooms, in thiscase).

The basidiocarpgills are lined withterminal dikaryoticcells called basidia.

4

Karyogamy in the basidia produces diploidnuclei, which thenundergo meiosis.

5

When mature,the basidiospores

are ejected, fallfrom the cap, andare dispersed by

the wind.

7

In a suitableenvironment, the

basidiospores germinate and

grow intoshort-lived

haploid mycelia.

8

Figure 31.20


• Concept 31.5: Fungi have a powerful impact on ecosystems and human welfare


Decomposers

• Fungi are well adapted as decomposers of organic material

– Performing essential recycling of chemical elements between the living and nonliving world


Symbionts

• Fungi form symbiotic relationships with

– Plants, algae, and animals


Mycorrhizae

• Mycorrhizae

– Are enormously important in natural ecosystems and agriculture

– Increase plant productivity

RESULTS

Researchers grew soybean plants in soil treated with fungicide (poison that kills fungi) to prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed mycorrhizae in the soybean plants’ roots.

EXPERIMENT

The soybean plant on the left is typical of the experimental group. Its stunted growth is probably due to a phosphorus deficiency. The taller, healthier plant on the right is typical of the control group and has mycorrhizae.

CONCLUSION These results indicate that the presence of mycorrhizae benefits a soybean plant and support the hypothesis that mycorrhizae enhance the plant’s ability to take up phosphate and other needed minerals.Figure 31.21

RESULTS


Fungus-Animal Symbiosis

• Some fungi share their digestive services with animals

– Helping break down plant material in the guts of cows and other grazing mammals


• Many species of ants and termites

– Take advantage of the digestive power of fungi by raising them in “farms”

Figure 31.22


Lichens

• Lichens

– Are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae

(a) A fruticose (shrub-like) lichen

(b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichensFigure 31.23a–c


• The fungal component of a lichen

– Is most often an ascomycete

• Algae or cyanobacteria

– Occupy an inner layer below the lichen surfaceAscocarp of fungus

Fungalhyphae

Algallayer

Soredia

Algal cell

Fungal hyphae

10

m

Figure 31.24


Pathogens

• About 30% of known fungal species

– Are parasites, mostly on or in plants

(a) Corn smut on corn (b) Tar spot fungus on maple leaves (c) Ergots on ryeFigure 31.25a–c


• Some of the fungi that attack food crops

– Are toxic to humans


Practical Uses of Fungi

• Humans eat many fungi

– And use others to make cheeses, alcoholic beverages, and bread


• Antibiotics produced by fungi

– Treat bacterial infections

Staphylococcus

Penicillium

Zone of inhibited growth

Figure 31.26


• Genetic research on fungi

– Is leading to applications in biotechnology

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