Plant Defenses

why r plants preyed on my herbivores and pathogens?

they lack an immune system and provide ‘easy’ to access rich, nutrient source.

Pathogens

Includes fungi, bacteria, viruses, nematodes, and other microorganisms that can infect a plant and cause a diseased reaction. Typically secondary to harm

what r the 3 types of pathogens?

• biotrophs

  • keep the host alive

• necrotrophs

  • kill host

• hemibiotrophs

  • biotrophs in early stages, then become necrotrophic

Biotrophs

Pathogens that keep the host alive and feed on living tissue (e.g. powdery mildew fungus)

Necrotrophs

Pathogens that overwhelm plant defenses, generating a quick release of nutrients (e.g. soft rot bacteria) kill host

Hemibiotrophs

pathogens that behave as biotrophs during early stages of infection, but then become necrotrophic (kill)

Fusarium Oxysporum f.sp. Cubense Fungus

Caused the Panama disease and wiped out production of the Gros Michel banana (in the 1950's)

Host-Range

Species that can be affected by a pathogen (undergo a diseased reaction)

Immunity

Complete lack of any disease symptom (disease can not even infect humans)

High Resistance

Some disease symptoms but not alot

High Susceptibility

Major disease symptoms

how do plants detect attacks?

1) innate immunity

2) hypersensitive response

3) systemic acquired resistance

Innate Immunity (Basal Resistance)

The first line of defense. Recognition of molecular patterns from pathogen trigger fortification of cells.

• pathogen can’t get in

Hypersensitive Response

Second line of defense, it involves the deliberate cell death to isolate infected area

• im infected so ill blow up to try to take it w me and save the rest of the plant

Systemic Acquired Resistance

Long-term response; resources mobilize to protect the plant from any future infection (non-specific)

• moves resources (like proteins or enzymes) to prevent future infections

herbivores

eats plant, not infects. most of the time is not lethal and decreases growth + reproduction of individuals

Granivores

herbivore that feed on seeds

Grazers

herbivore that feed on grasses and ground-growing plants

Browsers

herbivore that feed on leaves from trees and shrubs

Frugivores

herbivore that feed on fruits

Elicitors

A molecule that induces a broad type of host defense response which allows plants to recognize damage from pests (molecular patterns)

• plants may respond by releasing VOCs

Volatile Organic Compounds (VOCs)

how plants respond to the presence of elicitors. they can:

• Repel harmful organisms.

• Attract beneficial predators who prey on the pest (ex: cotton plants attract wasps that eat

harmful moths)

they trigger an immune response in neighborhing, undamaged plants!!

Structural (or Physical) Defenses

The first line of protection - they make it difficult for herbivores to eat a plant and block the entrance of pathogens.

• This includes cell walls, cell modifications, and physical structures

what is the first line of defense?

structural/physical defenses (cell walls, cell modif, physical structures)

Biochemical Defenses

Substances produced in cells and tissues that are either toxic or inhibit the growth/reproduction of attacking organism

Constitutive Defenses

Defenses that are always present in plants (regardless of whether it is damaged) like spines

Induced Defenses

Defenses that are triggered by an attack

Cell Wall

A major line of defense against pathogens - it's a major physical barrier and contains a variety of chemical defenses

• a structural defense

Lignin

Make tissue difficult to chew for small herbivores. They are a highly branched, heterogeneous polymer

• a structural defense

• a type of phenolic (secondary metabolite)

Cutin and Suberin

Impermeable waxy substances and prevent infection by pathogens and insects

• a structural defense

what r some structural defenses that r cell responses?

• papillae

  • callose deposits formed btwn cell wall and membrane to trap infection in one area

• oxidative burst

  • enzymes release highly reactive oxygens that blow up everything in area

• cork layers

  • several layers form beneath infection to protect further invation and cut off food + water

Papillae

Callose deposits formed between the cell wall and the cell membrane near the site of infection to prevent spread of pathogen

• trying to hold it @ site of infection so it doesnt spread “sticky trap”

Oxidative Burst

Enzymes catalyze the release of highly reactive oxygen molecules which damage invader AND cross-linkages between cell wall polymers

• disrupts/blows up everything in area

Cork Layers

Several layers of cork are produced below the point of infection - cutting food and water from infected areas, and preventing further invation

• layered protection

what modified cells r part of the structural defense?

• sclereids

  • irregularly shaped cells w/ thick secondary walls to make them hard to chew

  • thousands can form stone cells which r abrasive “sandpaper”

• stinging cells

  • shaped like needles that inject painful toxins

• raphides

  • contain calcium oxalate crystals which tear mouth tissue

Sclereids

Irregularly shaped cells with thick secondary walls making them hard to chew.

• Thousands of sclereids might form stone cells that can be abrasive to herbivore teeths “sandpaper’

Stinging Cells

Shaped like hypodermic needles, they break off when disturbed and can inject painful toxins

Raphides

Cells that contain calcium oxalate crystals which can tear mouth tissue of herbivores when ingested.

what r some physical structures that protect plants?

• spines

  • modified leaf

• thorns

  • modified stem

• prickles

  • modified epidermal outgrowth

• trichomes

  • modified epidermal cells + living

Spines

A modified leaf or leaf part (usually the petiole, central vein, or stipule)

Thorns

A modified stem that is hard and sharply pointed

Prickles

Hard, pointed epidermal outgrowth

Trichomes

Specialized epidermal cells; can form dense mats that make it difficult for insects to chew the leaf; some have glands to secrete chemical repellents

Primary Metabolites

Substances produced by plants that are directly involved in growth, reproduction, and essential functions (e.g. sugars, amino acids, nucleic acids, etc). Common to all plants and produced constantly as

Secondary Metabolites

Substances involved in other functions, such as plant defense. Can be turned on. They are more taxa-specific.

Taxas include:

• Terpenoids (largest class)

• Phenolics

• Alkaloids

Terpenoids

These are the largest class of secondary metabolites (> 22,000 compounds). antifungal + antibacterial properties

Includes:

• monoterpenoids + sesquiterpenoids → make up essential oils

• diterpenoids → strong antifungal + antibacterial

• triterpenoids → mimic steroid hormones

Essential Oils are made up of what and do what?

Oil that has the main components of monoterpenoids and sesquiterpenoids. This oil works as insect toxins, antifungal and antibacterial properties.

Diterpenoids

Terpenoids that have strong antifungal and antibacterial properties

Triterpenoids

Terpenoids that have similar structures to sterol and steroid hormones → messes up endocrine system of herbivores

phenolics

a group of secondary metabolites. They r produced by the shikimic and melonic acid pathways. Include:

• Flavonoids

  • ( most common) phytoalexins r produced in response to attack. (antifungal + antibacterial)

• Anthocyanins

  • water soluble pigment

• tannins

  • water soluble polymer, toxic to insects by binding to salivary enzymes

• lignin

  • highly branched, heterogenous

what is produced with the shikimic and melonic acid pathways?

phenolics like: flavonoids, anthocyanins, tannins, lignin

Flavonoids

Produced shikimic and melonic acid pathways. These are the most common phenol.

• Phytoalexins are produced in response to pathogen attacks (antifungal and antibacterial)

phytoalexins

antimicrobial chemical produced by flavonoids (a phenolic) in response to pathogen attacks

Anthocyanins

Produced shikimic and melonic acid pathways.(a phenolic) These are water-soluble pigments (can be found in paint)

Tannins

Produced shikimic and melonic acid pathways (phenolic). These are water-soluble polymers stored in vacuoles; toxic to insects as they bind to salivary enzymes

Alkaloids

Bitter-tasting nitrogenous compounds found in many vascular plants. It is derived from the amino acids aspartate, lysine, tyrosine and tryptophan

• a type of secondary metabolite

Includes:

• caffiene

• nicotine

• cocaine + morphine

• Capsaicin (spicy)

• atropine (neurotoxin)

• cyanogenic glycosides

what is derived from the a.a aspartate, lysine, tyrosine, and tryptophan?

alkaloids ( a secondary metabolite)

Caffeine

Addictive compound that is toxic to insects and fungi and has allelopathic properties

• a type of alkaloid

Nicotine

Addictive compound that is stored in vacuoles and released when leaf is damaged → anti-insect

• a type of alkaloid

Cocaine & Morphine

Addictive compound just like Nicotine and Caffeine

• a type of alkaloid

Capsaicin

Alkaloid that is contained in chili peppers and is responsible for spicy

Atropine

Alkaloid that is a neurotoxin and cardiac stimulator (powerful)

Cyanogenic Glycosides

Alkaloid that halts cellular respiration - source of cyanide (powerful)

how r proteins and enzymes used in defense?

they inhibit pathogen and pest enzymes by binding to their active sites. They are expensive energetically, so they r a secondary defense (made when attacked)

include:

• defensins

  • v diverse

• digestive enzyme inhibitors

  • give herbivores upset stomach

• hydrolytic enzymes

  • degrade cell wall of fungi

Defensins

Very diverse proteins, found in any type of tissue. They are in plants and seeds and inhibit pathogen and pest enzymes by binding to their active sites

Digestive Enzyme Inhibitors

Alpha-amylase & Protease inhibitor → give herbivores an upset stomach

Alpha-Amylase

Starch digestion in legumes

• digestive enzyme inhibitor

Protease Inhibitor

Binds to several enzymes (like trypsin and chymotrypsin)

• digestive enzyme inhibitor

Hydrolytic enzymes

Degrade the cell wall of pathogenic fungi ANTIFUNGAL!

what r some other plant defenses?

• bioaccumulation of minerals toxic to animals ( like cadmium + selenium)

  • stores it in vacuole for when herbivore tries to eat it. V potent!

• nutritionally poor shoots

  • amt of nutrients low in shoots so grazers wont want it

• ecological defenses (symbiosis)

  • plants form symbiosis w beneficial microbes or insects that provide protection