Mycorrhiza-Plant Interactions

So You Think You Are Alone

Plant Nutrients

Just like us, plants require nutrients

C HOPKINS CaFe Mg- essential plant nutrients

Unlike us, (usually) plants do not get their nutrients from the food they eat. Instead get their nutrients from the surrounding environment

Exception-Carnivorous Plants

Carnivorous plants often found in low nutrient environments.

Major Sources of Nutrients Absorbed by Plants

Chapin, Matson, Mooney

Table 7.1. Major Sources of Nutrients that Are Absorbe d by Plantsa.

Source of plant nutrient (% of total)

Nutrient Deposition/fixation We athe ring Recycling

Temperate fore st ( Hubbard Brook)

Nitroge n 7 0 93

Phosphorus 1 < 10? > 89

Potassium 2 10 88

Calcium 4 31 65

Tundra (Barrow)

Nitroge n 4 0 96

Phosphorus 4 < 1 96

a Data from [Chapin, 1980 #1564; Whittaker, 1979 #2812]

Roots

• Function of Roots

– Nutrient uptake

– Water uptake

– Support

– Storage

Types of Root Systems

Grass Roots

Desert Tap Roots

RootsRoot Tip

Most Nutrients Are Picked Up By Diffusion

– Rates of diffusion depend on concentration gradient

• Rates of nutrient uptake are higher when the soil nutrient concentration is higher

– Rates of Mineralization and decomposition

– Amount of Fertilization

Depletion Zones

• Nutrient uptake by the root causes there to be a zone of nutrient depletion around the root

– Roots need to keep growing to explore new soil

Chapin, Matson, Mooney

Increasing root area is main way plants can increase nutrient

uptake

• Increased root:shoot ratio

– Increased investment in roots

• Root proliferation in nutrient hot spots

– Root growth occurs where it does the most good

• Longer root hairs

Root Shoot Ratios Depend on Soil Nutrient Supply

Effect of Soil Phosphorous on Root: Shoot Ratios

Low Soil Phosphorous Content

Root Mass (mg Shoot Mass (mg) Root:Shoot Ratio223 877 0.24

High Soil Phosphorous Content

Root Mass (mg Shoot Mass (mg) Root:Shoot Ratio209 1324 0.16

Q: Why are fine structures like hyphae and root hairsparticularly effective at nutrient absorption?

A: Have high surface area.

Q: For a given volume (or mass) of roots, what size rootpresents the most surface area?

Surface area of a cylinderSA = circumference x length

SA = x diam x lengthSA = x 2r x length

Volume = area x lengthVol = x r2 x length

SA/Vol = ( x 2r x length)/( x r2 x length)

SA/Vol = 2/r

As the radius decreases, the surface area per volume increases.

Importance of Diameter For Nutrient Uptake

Most Plants Have Formed Symbiotic Relationship with Fungi

• Need to know something about fungi.

Fungi

• Unique, weird, interesting, and important group of organisms

– You should be able to tell us

– About their basic biology

• How they are unique

• Why they are weird

• Why they are interesting

• Why they are important

Fungi

• Eukaryotic, spore-bearing, heterotrophic organisms that produce extracellular enzymes and absorb their nutrition.

• Functional definition

Fungi vs. "fungi"

• Based on the functional definitions of fungi, fungi do not comprise a single monophyletic group of organisms

• more than one evolutionary origin

• not all "fungi" are members of the Kingdom Fungi Fungi

Fungi

• The Kingdom Fungi includes some important organisms, both in terms of their ecological and economic roles. – break down dead organic material

• Nutrient cycling

– most vascular plants have mycorrhizae– provide numerous drugs

• E.g., penicillin

– Provide food • mushrooms, truffles and morels• Involved in producing bread, wine. champagne, and beer.

Fungi

• Cause a number of plant and animal diseases

– Humans

• ringworm, athlete's foot, and several more serious diseases are caused by fungi.

– Because fungi are more chemically and genetically similar to animals than other organisms, this makes fungal diseases very difficult to treat.

– Plant diseases

• rusts, smuts, and leaf, root, and stem rots, and may cause severe damage to crops.

Fungi

• About 100,000 species have been described

– Some have suggested that there might be over 1 million species of undescribed Fungi

Fungi Systematics

• Fungi are usually classified in four divisions: – Chytridiomycota (chytrids),

– Zygomycota (bread molds)

– Ascomycota (yeasts and sac fungi)

– Basidiomycota (club fungi).

• Classification based on the way in which the fungus reproduces sexually. – The shape and internal structure of the

sporangia, which produce the spores

Chytridiomycota

Mainly Aquatic

Zygomycota

Ascomycota

Basidiomycota

Fungi Systematics

• The Deuteromycota includes all fungi which have lost the ability to reproduce sexually.

– Don’t know which group they should be placed

• Deuteromycota becomes a convenient place to dump them until someone gets around to working out their biology.

Fungi Systematics

Lichens are not a single organism, but rather a symbiotic association between a fungus and an alga.

– The fungus is usually an ascomycete or basidiomycete

– the alga is usually a cyanobacterium or a green alga.

• Often the fungal partner is unable to grow without the algal symbiont, making it difficult to classify these organisms.

Lichens

fungi that are not Fungi

• It should also be noted that some organisms carry the name of mold or fungus, but are NOT classified in the Kingdom Fungi.

• These include the slime molds and water molds (Oomycota).

– The slime molds are now known to be a mixture of three or four unrelated groups

– oomycetes are now classified in the Chromista, with the diatoms and brown algae.

Fungi that aren’t Fungi

Slime Mold Water Mold (growing on aquatic insect)

Fungal Organelles

• Fungi are eukaryotes so they share the normal eukaryotic organelles

– Lack cholorplasts

• Fungal organelles

– Spitzenkorper

• associated with growing hyphal tips in septate fungi

– chitosome

• microvesicles transporting chitin synthases to growing cell wall

Cell Wall

• chitin

1-4 n-acetyal glucosamine

• -glucans

polymers of glucose

1-3 glucose

• cellulose

• Key Point

• Fungal cell walls

different from plant

cell wallsin some

Chitin

Cellulose

1-3 glucan

Body Plan• unicellular (yeast), filamentous, or both (=dimorphic)

• Hypha (pl. hyphae) is the basic “cellular” unit in filamentous fungi; they may be septate or coenocytic(aseptate);

• collectively known as a mycelium

• limited tissue differentiation and division of labor

Nuclear Status

• Eukaryotic; uni, bi- or multinucleate

• Haploid, diploid (less frequent)

• Monokaryon

(1 nucleus per hyphal compartment)

• Dikaryon

(2 nuclei per hyphal compartment)

• Homokaryotic

• Heterokaryotic

Feeding• Heterotrophic

• Secrete extracellular enzymes

• Absorptive nutrition

• Saprobes

• decay dead organic matter

• pathogens

• symbionts

• Parasites, commensals, mutualists

Reproduction

• Sexual reproduction:

• spores meiotically produced nuclei

• Asexual reproduction

• Spores with mitotically produced nucleiierivenuclei

Spores - a minute propagative unit functioning as a seed, but differing from it in that a spore does not contain a preformed embryo

Fruiting body - any complex fungal structure that contains or bears spores; a sporocarp

Seeds vs Spores

• Seeds

– Embryo

– Larger

– Resources for developing seeding

Sexual Reproduction in Fungi

• Homothallic (selfing)

• Heterothallic (outcrossing)– Monoecious or dioecious

• Genetic mating system

– Different Mating Types• Generally can’t mate with someone with same mating type

– 1 to hundreds of mating types

– Some people use “mating types” and “sexes” as synonyms

What is a “Sex”?

• I prefer to distinguish between mating types and sex.

• Questions:

– How many sexes in humans?

– How many sexes are you?

Sexes in Humans

• We consider that humans have two sexes– Females and males

• What distinguishes males and females?– In humans individuals that produce eggs (female

gametes) are called females

– Individuals that produce sperm (males gametes) are called males

• Humans are “dioecious”– Female and male gametes are produced in different

individuals

Hermaphrodites• Some species (earthworms, sea hares, lots of

plants) produce both male and female gametes

– Hermaphrodites

– Monoecius

Do All Sexually Reproducing Species Produce Two Species?

• What does it mean to have two sexes?

• What would it mean to have one, three, or eleven species?

What Would It Mean to Have Other Than Two Sexes?

• We produce two types of gametes

– Consider that we have two sexes

• Let’s think about our life cycle?

Life Cycle of Humans

?

The Prom

Engagement

Wedding

Honeymoon

Wedding Night?

Wedding Night

• Meiosis

– Eggs and sperm

• (Censored)

• Fertilization

• Zygote Formed

Development

Baby Develops

Nine Months Later

Human Life Cycle

• Gametes (haploid) produced by meiosis

• Haploid gametes join to make zygote (diploid)

• We have “alternation of generations”

– Both diploid and haploid stage of our life cycles

Aside

• When does life begin?• Actually a very difficult

question to answer because of the life cycle, life never really stops.

• Not a question that science can answer

Back to Number of Sexes

• We produce 2 types of gametes – Therefore we have two sexes

• Difference in Size and Function of Gametes– Female gametes (eggs)

• Large

• Immobile

– Male gametes (sperm)• Small

• mobile

What Would It Mean to Have Three Sexes

• Three sizes and function of gametes?

– Small mobile gametes

– Large immobile gametes

– Intermediate-sized mobile gametes

• What happens during fertilization?

• No species that have three sexes

What Would it Mean To Have Only One Sex?

• One size and function of gamete.

– Mobile

– Contain resources

• Swimming Egg

• Huge Sperm

Isogametes

• Chlamydamonas– Green algae– Single celled– Haploid as adults– aquatic

• Single celled• Photosynthetic• Eye spot

• Haploid adult produces isogametes by mitosis– Haploid, mobile, contain

energy

Isogametes

• Isogametes are evolutionarily “primitive”

– First organisms that reproduced sexually via gametes were isogamous

• Oogametes (egg and sperm) are evolutionarily advanced

• Oogametes arose from isogametes via disruptive selection

Modes of Natural Selection

Large gametes- contain more

resources, thus mighthave higher survival once fertilized

Small gametes- can make more of

Them and the might be More mobile, thusFertilize gametes more often

SelectionAgainst middle-Sized gametes

Female gametes- specialized for

Providing resources to embryo

Male gametes- specialized for

mobility during fertillization

Plant-Fungi Interactions

• Number of different types of interactions between fungi and plants

Mycorrhizae

• Mycorrhizas are symbiotic associations essential for one or both partners, between a fungus and a root of a living plant, that is primarily responsible for nutrient transfer. – Mycorrhizas occur in a specialized plant organ where

intimate contact results from synchronized plant-fungus development.

• The name mycorrhizas, which literally means fungus-root, was invented by Frank (1885) for non-pathogenic symbiotic associations between roots and fungi.

Types of Mycorrhizae

• Ectomycorrhizal fungi

– are mostly basidiomycetes that grow between root cortical cells of many tree species, forming a Hartig net.

• Arbuscular mycorrhizal fungi

– form highly branched structures called arbuscules, within root cortical cells of many herbaceous and woody plant species.

Ectomyhcorrhizae

• Produce hyphae between root cortical cells producing a netlike structure called the Hartignet

Ectomycorrhizae

• Found on woody plants ranging from shrubs to forest trees

– Pinaceae (Pines)

– Fagaceae (Oaks)

– Betulaceae (Beeches)

– Myrtaceae (Myrtles)

Ectomycorrhizae

• Over 4,000 fungal species, belonging primarily to the Basidiomycotina, and fewer to the Ascomycotina, are known to form ectomycorrhizae.

• Many of these fungi produce mushrooms and puffballs on the forest floor.

• Some fungi have a narrow host range while others have very broad host range– Some species of fungi forms ectomycorrhiza with

more than 46 tree species belonging to at least eight genera.

Vesicular Arbuscular Mycorrhiza

Inside root

• Intercellular mycelium

• Intracellular arbuscule

• tree-like haustorium

• Vesicle with reserves

Outside root

• Spores (multinucleate)

• Hyphae

•thick runners

•filamentous hyphae

Form extensive network of hyphae

even connecting different plants

Arbuscule of Glomus mosseae – branching provides large surface area

Arbuscular Mycorrhiza

Arbuscular Mycorrhiza

• Form highly branched arbuscule within root cortical cells.

• The fungus initially grows between cortical cells, but soon penetrates the host cell wall and grows within the cell.

• The general term for all mycorrhizal types where the fungus grows within cortical cells is endomycorrhiza. I

Arbuscular Mycorrhizae

• Glomales (130 species – infects 300,000 plant species)

• Found on roots of herbaceous angiosperms, most trees, mosses, ferns…

• not present on Cruciferae, Chenopodiaceae, Proteaceae

• small biomass compared to roots

Mycorrhizae and Orchids

• Orchids typically have very small seeds with little nutrient reserve.

• The plant becomes colonized shortly after germination, and the mycorrhizal fungus supplies carbon and vitamins to the developing embryo.

Root hair Smallest hyphae

• Roots and root hairs

cannot enter the smallest

pores

• Hyphae is 1/10th

diameter of root hair

• Increased surface area

•Surface area/volume of a

cylinder:

SA/vol ≈ 2/radius

Why Mycorrhiza?

Why Mycorrhiza?

Inoculated with

mycorrhizae

Not inoculated with

mycorrhizae

Plant-Mycorrhizal Interactions

• Mycorrhiza have been shown to increase rates of nutrient (especially phosphorous) uptake

• May also increase rates of water uptake

Plant-Mycorrhizal Interactions

• General Trends

– Because mycorrhiza increase rates of nutrient uptake plants “infected” with mycorrhizae have lower root/shoot ratios

– Usually mutualistic relationship

• Plants benefit from increased nutrient uptake

• Mycorrhiza benefit from carbon

My Former Research at Tech

Importance of Animal-Generated Disturbances

• Open potential germination sites by removing leaf litter

• Create patches that differ

– Nutrient content

– Microbial content

Experimental Approach

• As part of a larger experiment we grew plants in soil from different disturbances

– Gopher mounds

– Bare space

– Rabbit mounds

• With and without mycorrhiza

Schizachyrium scoparium

Experimental Design

• Grew seedlings in “conetainers” in greenhouse

• Sterilized soil (heat)• Selectively added back

microbes (sterilized, + mycorrhiza, + bacteria, + both)

• Grew seedlings– Growth rate, root &

shoot biomass, mycorrhizalifection

Some Results

• Plants infected with mycorrhiza had lower root/shoot ratios

• Soil from rabbit mounds– Higher in nitrogen

than surrounding soil (equal in all other nutrients)

Results

• Prediction– If mycorrhiza-plant interaction is mutualism then

plants infected with mycorrhiza should grow better than plants grown in sterilized soil

• Observation– Plants grown in sterilized soil were larger than

plants infected with mycorrhiza

– Mycorrhiza acted as parasite in high nutrient environments.

Current Research in the Field

• Experts in coevolution, plant biology, and fungal biology are working together to examine this incredibly complicated mutualism

– Active area of current research in all three fields