Plant Bio 40 Final Exam

Plant Hormones

Can signal to each other, and help plants work out how to grow organs (tells things where to grow and communicate to the cells)

Auxin

• Hormone - controls growth (discovered by Charles Darwin, uncovered by Fritz Went, f

• Found in the tip of shoot, light source will diffuse it to other side of plant, will promote shaded side to elongate and bend towards light source

• Induces organ formation, promotes growth of new roots, helps plants heal after wounding

Gravitropism

Auxin promotes growth and can also respond to gravity - causing a plant to grow in response

Ethylene

• Key regulator of fruit ripening, is found in high concentrations of bananas

• A gas - can travel between plants, induced upon wounding

• Can also act as a signal for neighboring trees to produce increased levels of tannins

Gibberellin

• Growth accelerating hormone in plants - interrupts growth suppressors - too much growth could be a bad thing

• Treating fruit with this hormone makes them larger but seedless, this hormone can end dormancy to promote seed germination

Abscisic Acid

• This acid will prevent flowering and seed germination - this helps conserve resources during stress!

• Signals to plants to slow down growth and conserve resources during stress - helps with drought response by closing the stomata

• Pauses summer photosynthesis

Deciduous

• Trees that lose their leaves in the winter, caused by ABA

Microbiomes

• Every human body has more bacterial cells than human cells!

• Bacteria can be friendly - and help with gut inflammation, acne, asthma, allergies

• A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria

Plant-Microbe Interactions

• Plants are able to cultivate populations of friendly microbes within the rhizosphere

Rhizosphere

The soil surrounding the root system

Rhizobium

• Functions:

  • Converts phosphorus and sulfur to the right chemical forms for plants to take in

  • Enhance mineral uptake

  • Protect against metal toxicity in soils

  • Nitrogen fixation in legumes

  • Production of plant hormones to alter development (like auxin)

Siderophores

• Rhizobium produces these molecules, which harvest iron from the soil to provide it to plants

Nickel Hyperaccumulators

• Some plants accumulate tons of nickel - they could help restore habitats destroyed by mining

Nitrogen-fixation in plants

• Rhizobium helps legumes fix nitrogen from the air in root organs called nodules

Nitrogenase

• Rhizobium contains this enzyme, which converts atmospheric nitrogen into nitrogen the legumes can use

Cycads

• Ancient trees that release chemicals to “convince” cyanobacteria to invade roots, which fixes nitrogen

Azolla

• A tiny aquatic fern that hosts a cyanobacteria that fixes nitrogen. This increases nitrogen available in water and soil.

Frost Damage

Ice is very damaging if it forms within and between cells in the leaf - ice can shear through cells and break them

Ice Nucleation Proteins

• Two proteins interlock, form big particles around which allows ice crystals to form - produced by bacteria

“Ice-minus” Pseudomonas

• Scientists made a genetic mutant of pseudomonas which prevents frost damage

BlightBan

• A different pseudomonas species which is used to fight frost - which naturally lacks the ice nucleating protein organically

• Bioprecipitation

• The hypothesis that pseudomonas in clouds could make it rain or snow.

Bacteria-free seeds

• Montana State scientists planted 20 tons of bacteria-free seeds in an isolated field. 3 weeks later, pseudomonas colonized seedlings and the clouds!

Cyanobacteria

• Blue green algae, can convert light energy into chemical energy

Mixture of Beneficial Bacteria (importance)

• Coating seeds with this can enhance growth

Pseudomonas syringae

• Produces a protein that is efficient in “nucleating” ice formation

Plant Disease

• Wipe out 16% of global crops every year, and can decimate the environment

Sudden Oak Death

Current epidemic in California

Chestnut Blight

From 3 billion to <100 trees in Eastern US

Plant Pathology

The study of plant diseases and how plants resist them

Potato Blight

• The most famous plant disease on the most important dicot crop

Potato History

• Domesticated in Peru, brought to Europe in 16th century and became the staple crop in Ireland

The Disease Triangle

• 3 factors required for infection - susceptible host, virulent pathogen, favorable environmental conditions for disease

How does fungus infect potatoes?

Phytophthora spores land on leaves, hyphae invades leaves via stomata, then spreads throughout tissues while feeding on cells, pushes up through dead tissue to create spores on plant surface

What caused the Irish potato famine?

• Oppression, imperialist politics, genetic uniformity, lack of protective microbes, food supply

Heinrich Anton deBary’s potato experiment

• He discovered how spores can cause disease instantly by being in contact with a potato

R Genes

Confer disease resistance (and are highly sought after!) They encode resistance to a pathogen, like antibodies

How can a plant recognize a pathogen?

• Pathogens evolve quickly to avoid recognition, but plants adapt fast, dedicating parts of their genome to being “R gene factories”

How do viruses work?

• They hijack host genes/proteins to propagate

Programmed cell death

• Extreme response - plants can kill infected cells to stop a virus from spreading

Tulip Breaking Virus

• Tulip mania occurred in 1600s because TBV affected the color of tulip cells and made them extremely rare

Fungi

NOT plants! - break down dead plants within soil, form networks with plants underground, agents of plant disease, partner with algae to form lichens

Parts of Fungi

• Single unit of a fungus is a hypha

• These form vast branching networks called mycelium

• The fungi you can see (mushrooms) are fruiting bodies

Hyphae

• Microscopic highways for nutrient transport

Could fungi help dispose of plastics?

• Fungal growth is strong enough to break through plastic, even in weeks!

Plant-fungi interaction

They recycle plant nutrients into the soil, secreting digestive enzymes outside their cells and absorbing whatever is nearby

Carbon Cycle & Fungi

They absorb CO2 but send most back into the atmosphere, making it carbon neutral

Mycorrhizae

Fungus + root - most plants have underground relationship with fungi

Arbuscules

Little Tree - Fungi invades root cells and forms these, which help with nutrient transfer

Nutrient Cycling

Fungi triggers cooperation, fungi gets plants hooked on their product, fungi moves resources to increase value, and hoards resources to retain higher prices

Wood Wide Web

Links species together, creates nutrient transfer between them and loaning nutrients during off season

Ghost Plants

Some plants abandoned photosynthesis, have no leaves, get all of their nutrients from fungi

Lichens

• Symbiotic colonies of algae and fungi - they benefit from photosynthesis of algae and versatility of fungi

• Can eat rocks and inhabit difficult places, can dig into rocks, feed off bark, grow on whatever

• Most grow very slowly because they use so much energy for other things.

Pollination

How plants solve the problem of mating

Stigmas

Have evolved to trap pollen

Anthers

Pollen factories

Exine

Pollen wall - tough

Sporopollenin

Polymer that makes up pollen wall

Apertures

Pores in pollen

Pollen delivery

Smallest grains are wind dispersed, bigger grains are animal dispersed. Each plant produces millions of them.

Pollen

Tough outer exine is made of sporopollenin, a tough polymer, and stays intact for thousands of years. Apertures let the sperm nuclei exit during reproduction

Plant Fertilization Process

Pollen delivers sperm cells via pollen tubes. Pollen tubes grow fast, reach down to ovules

How do plants attract pollinators?

Petal color, petal surface/pattern, petal shape/mimicry, scent, nectar

Petal color

• Bees are attracted to purple/blue, birds are attracted to red/orange, butterflies are attracted to everything, and bats are attracted to white

• Evolves very quick (1 gene) 

Petal surfaces/patterns

Crinkly cell surfaces make some petals iridescent

Floral shape/mimicry

• Cone shaped petals make the surface easier to grip by insects

• Mimicry - attracting pollinators’ via their mating behavior

Scent

• Some can produce sex pheromones of a bug!

• Some just smell really good

• Some smell like rotting flesh to attract pollinators

Nectar

Photosynthesis allows plants to produce lots of sugar - flowers have evolved glands that release sugar to feed pollinators

Primary Metabolism

Basic, necessary for life chemical reactions that happen in plants. (photosynthesis, respiration, sugar synthesis, starch synthesis)

Secondary Metabolism

A toolkit to interact with the environment (pigment, poisons, scents, polymers)

UV Light

Reveals markings visible to only insects, can also protect flowers from sunlight

Secondary Metabolites

Glucosinolates, Tannins, Terpenes, Cyanides, Alkaloids

Glucosinolates in Brassica

Toxic to insects, released upon wounding the plant (don’t boil broccoli or brussel sprouts!)

Tannins

• Defense compounds humans enjoy. Causes astringency - like drinking red wine and tea

• Can be bitter and toxic at high qualities!

Terpenes

• Airborne plant chemicals that create smells

• Like linalool, limonene, pinene, etc

• When you crush a plant, releases terpenes

Herbivory in Agriculture

Insect herbivores can decimate crops

Herbivory

• The state or condition of feeding on plants

Alkaloids

Caffeine, opium, nicotine, change an animal’s sensory and mental state

Trichomes

Giant cells that contain defense chemicals (leaf hairs)

Atropine

Produced by deadly nightshade, can kill humans, but in low concentrations used for pupil dilation, anaesthesia, and treating pesticide poisoning

Cyclopamine

An alkaloid poison - caused birth defects in sheep

Cyanide

Simple, highly toxic chemical - causes death (in apple cores)

Diamondback Moths

Evolved resistance to glucosinolates, enzymes can break them down - they are attracted to it!

Volatile Plant Hormones

Signal defense against herbivores as well, warns other plants, can work across species!

Isoprene

What terpenes are made of - what makes mountain ranges look hazy blue

Insect Herbivores can Decimate Crops

Like the colorado potato beetle, a major pest of potato crops, 15% of crop yield is gone!

Pesticides are a mixed blessing

• Pesticides are extremely effective against insect herbivores

• They have saved a lot of people from world hunger

DDT

Extremely damaging for the environment and had to be banned, stops insect nervous systems,

Modern Medicine and Plant Biology are Intertwined

• 50% of prescription drugs are based on a molecule naturally occuring in plants

• 25% of all prescription drugs are directly copied from plants

• 80% of the world’s population relies on herbal remedies of some kind

Medicinal Plant History

• Have been used since the beginning of civilization

• Super old dead people found with medicinal plant seeds

• Primates use medicinal plants as well, helps get rid of gut parasites

Aspella Leaves

Provides no nutritional value and can upset the stomach, but rids chimps of gut parasites

Catnip & Humans

Catnip has value as an insect repellent, so it’s encouraged as a mild sedative in humans

Artemisinin

Because sweet wormwood is poisonous, Tu Youyou extracted this to help treat malaria

Salicylic Acid

Aspirin is a synthetic copy, willow bark was historically used to help with fever

Medicinal Plants

Anti inflammatory, anti malarial, anti cancer, mind altering

Anti-inflammatory plants

Inflammation is helpful, but can cause painful discomfort, so we can use sage, thyme, mint, fennel, cilantro to remove bacterial in the gut

Antimalarial plants

Cinchona bark helps aid malaria, quinine water helps malaria, and sweet wormwood has been used although it is poisonous

Anti-cancer plants

Pacific yew is dangerous but contains Taxol which can be anti-cancer

Mind-altering plants

Coca plants contain cocaine, St John’s Wort can be used as an antidepressant, Mescaline is in cactus, Ayahuasca, Iboga as an alkaloid

Madagascar Periwinkle

Contains beneficial alkaloids, chemotherapy benefits, but only in tiny qualities so scientists treated it with plant hormones. It is expensive to produce as well, maybe we can find the enzymes that plants use to make these alkaloids?