Don't eat me: Human uses for plant

chemical defenses

Instructor: Dr. Steven Chatfield

Email: steven.chatfield@carleton.ca

stevechatfield@yahoo.com

– Protect plants & their resources (& our crops..) • Lots of high energy, complex organic molecules they‟ve

synthesized from inorganic substrates using the energy from

sunlight.

• Including reserves of storage molecules

• Herbivores, insects, nematodes, fungi, bacteria & viral

pathogens

– Worldwide pre-harvest crop losses: • 14% from insects

• 12% from disease

• 10% from weeds

– Additional losses post-harvest include: • Worms & insects feeding on seeds/storage organs

• Fungal & bacterial attack (e.g. Erwinia)

Plant Chemical Defenses, why are

they Important?

– Human uses:

• Therapeutic Drugs

• Religious & cultural roles

• Pesticides, microbicides, herbicides & poisons

• Flavours

• Pigments & dyes

• Construction & fabrication

• Perfumes & scents

• Recreational uses

Plant Chemical Defenses, why are

they Important?

• What are a plant‟s defenses

• Where do chemical defenses come from and

how are they made – How are they grouped?

• What uses have humans put them to

• What uses may humans put them to in

future?

Breakdown

• Plants are immobile, but not helpless

• An array of defenses – Constitutive = there all the time

– Inducible = attacker is detected & a defensive Response is mounted

• First line of defense against pathogens = waxy cuticle + cell walls (example of constitutive def.)

• Chemical defenses against large herbivores often at least partly constitutive

The defenses

• Some morphological defenses against

herbivores & insects (e.g. thorns &

hairs) but most Defenses involve

complex biochemistry

• Plants use >60,000 different

secondary metabolites

• Up to 10% of the dry mass of a plant

may Constitute defensive chemicals

– Historically humans selected for reduced

chemical defenses

– Occasionally they select for more (up to

25% DW!)

• Often stored in vacuole, some present

in apoplast or cell walls, some are

secreted or presented in surface

structures (often trichomes)

Secondary metabolites

Rob Schuurink UVA Netherlands

Tomato glandular trichomes

• TERPENES

• ALKALOIDS

• PHENYLPRONANOIDS

Secondary metabolites: 3 broad

chemical groups (+“Others”)

sesquiterpene alkaloids

Glycosides = Sugar groups added

Glucosinolates = glucose + amino acid

• TERPENES:

• >25,000 terpenes

• 5C skeleton (isoprene) sub-unit

– Smaller terpenes (5C- 10C) volatile & released by epidermal gland

cells as in flowers

• Perfumes

– Larger ones may be constituents of oils or resins or waxes

Terpenes

• Terpenes include essential oils found in herbs & spices

– Give peppermint, basil or sage their smells & aromatic substance in resin of wounded conifers

– Medicinals e.g. the sesquiterpene lactone Artemisin. See also Ginseng

– Flavours e.g. Liquorice

• Volatility useful to:

– Warn insects/herbivores of plant toxicity

– Attract insect pollinators or herbivores to eat fruits

• Terpenes also include allelopathic agents, insecticides & anti-herbivore agents

Terpenes

Citrus secretory cavities Gymnosperm resin ducts

• Terpenes also include some allelopathic agents, insecticides & anti-herbivore agents

• Organic Herbicides/weed suppressors?

• Signals for disease-causing organisms & parasites – Strigolactones & Striga spp (Witch Weed)

Allelopathic agents

=

Compounds released by one

plant to affect the growth of

another

Terpenes

Effect of Bitou bush terpenes on Banksia germination

Weed Ecology, UOW, Australia

• Carotenoids = 40C

terpenes e.g.

– Lycopene which gives

tomato its red colour &

beta-carotenes colour

many fruits & vegetables

(highest levels in carrot)

• Carotenoids useful as:

– Antioxidants: ring

structures absorb high

energy electrons

– Beta-carotenes used to

synthesize Vitamin A

Terpenes: Carotenoids

Lycopene: Proven efficacy in preventing stroke and some cancers

• Terpenes also used for

steroid metabolism • Plants use steroids against animal

pests E.g.

– Digitoxin (Foxglove), a cardiac

glycoside. Oleadrin too

– Phytoecdysteroids: mimics

insect moulting hormone

ecdysone & wreak havoc on life

cycle of pest

• Pyrethrin: toxic to insects, spiders,

ticks (and fish), but apparently not

mammals

Terpenes: Building blocks for

steroids

• >12,000 types

• Synthesized from amino acids tryptophan, tyrosine, phenylalanine, lysine & arginine

– All contain Nitrogen

• Target Nervous System. Used medicinally & otherwise As stimulants & sedatives e.g.

– Codeine & morphine from opium poppy

Alkaloids

• Example alkaloids:

– Codeine & Morphine from Opium Poppy

– Atropine & Scopolamine from Deadly Nightshade (Belladonna) Datura & Henbane

– Caffeine from Coffee

– Ephedrine from Ephedra

– Cocaine from Coca

– Nicotine from Tobacco

– Mescaline from Peyote

– Piperine from Black pepper

– Berberine from Barberry

– Antofine from DSV

– Quinine from Chincona spp

– Strychnine from Strychnos nux-vomica

– Aconitine from Aconitum spp

Alkaloids

• Hemlock contains the alkaloid poison

coniine. Killed Socrates

– Mistaken for wild parsley

• Many crops contain traces of very toxic

alkaloids e.g. solanine in potato

– Reduced from higher levels in wild

relatives by human selection

• Nicotine is a very effective insecticide &

more toxic (0.5–1.0 mg/kg) than strychnine

– Nicotine production up-regulated by

insect attack & grazing

• Caffeine kills the larvae of the tobacco

hornworm by inhibiting an essential

enzymatic reaction

• Coffee & tobacco = alkaloids as harvestable

commodities

Alkaloids

• Phenyl ring of 6C & a 3C Tail

– Often OH group (phenolics)

• Derived from phenylalanine (or tyrosine) through loss NH2 group

– Same precursors as some alkaloids but no N

• Compounds in cell wall

– Structural & waterproofing role & hence essential for adaptation of plants to land

• Includes the phenolics = 6C ring with OH = 40% of organic carbon in biosphere

• Plant use summary: – Structural, defense & protection,

pigments, attractants, UV

• Human use summary: – Construction, antimicrobial/rot

prevention, scents, pigments/dyes, flavours, medicine

Phenylpropanoids >8000 compounds

• Lignins are the prevalent phenolics

– Component of cell walls/WOOD

– Toxic to most microbes

• Lignin = complex polymer of phenol strength, water proofing, protection from microbial degradation

– 20-30% d/w vascular plants

• Lignin often produced after pathogen attack or wounding (to seal up & protect exposed surfaces (structural & toxic)

– Suberin (browning at cut edge)

Phenylpropanoids: Lignins

Wood tar

The Carboniferous

• Tannins (like lignins) are

polymers of phenols

• Tannins react with proteins

– Makes them less digestible

– High tannin content deters

herbivores.

– Tannins often have an unpleasant

taste

• Used by humans to process

protein in animal skins to make it

resistant to degradation by

microbes

– Tanning leather (E.g. using

acorns)

• Some medicinal uses e.g. anti-

inflammatory, antiviral,

antibacterial, hereditary

hemochromatosis,

Phenylpropanoids: Tannins

• Flavonoids (~4500 compounds)

• Give flowers their colour as pigments

• Flavonoids often found inside plant cell vacuoles

• Some flavonoids also feeding deterrents and signaling molecules

– E.g. legume-rhizobium signal released into soil from roots

• Lots of health claims: cancer, anti-inflammatory, heart health,

antibacterial. No FDA-approved claims as yet

• Some may have activity against crop diseases

Phenylpropanoids: Flavonoids

• Coumarins ~1500 types are flavonoids . Includes anticoagulants and light sensitizing chemicals

– Rodenticides, medicinals

• Psoralen (a flavonoid) is derived from celery & has been used to treat skin disorders

• Includes anticancer drugs such as taxol (part terpene, part flavonoid)

• Plant phenolics contribute to fragrances & flavours, E.g. vanillin & capsaicin

Phenylpropanoids

• Plants produce up to 300

non-protein amino acids.

• Seeds eaten & „fake‟ aa‟s

get incorporated into

herbivore proteins

rendering them non-

functional

• The plant‟s own translation

mechanisms can

distinguish these non-

protein amino acids

“Others”: Non-Protein amino acids

BMAA produced by cyanobacteria

Some other non-protein amino acids mimic neurotransmitters

Canavalia ensiformis

• Inhibitors of digestive enzymes:

– Some plants produce amylase

inhibitors & protease inhibitors

– Inhibit digestion of starch &

protein in the gut by direct

binding to the enzyme

• Thiaminases:

– Enzymes that breakdown

vitamin B1

– Ferns & Horsetails

Plant poisonous proteins1

• Lectins/phytohaemagglutinins: – Found in many beans

– Proteins that bind specific sugars on cell membranes • Recognition

• Resistance to pests

– Some can damage intestinal lining

– Some cause cells to stick together

• Uses – Science & medicine

• Blood typing

• Purification

• Antimicrobials

– Chemical warfare/bioterrorism

Plant poisonous proteins2

• Protein synthesis blockers:

– Irreversible inhibition of ribosomes (2000+ a minute) amongst the most toxic natural compounds (1 Molecule can kill a cell)

– Most famous is ricin from castor bean

• Much more deadly than cobra venom when injected

– “Umbrella assassinations”

– Protein = partial immunity possible

• Abrin from rosary pea is 75X more toxic than ricin?!

Plant poisonous proteins2

• Food crops bred for edibility and yield

– Inadvertent selection against defense chemicals?

– Inadvertent selection against flavour in modern ag/hort systems?

– Inadvertent selection against nutritional value

– Efforts to breed back in some of these beneficial traits

The future of plant secondary

metabolites?

Dave Liscombe Vineland Research

• Secondary metabolites & Medicine – Unexplored

– Underexploited

– Untested potential

• Exciting area of research

The future of plant secondary

metabolites

Myron Smith & Owen

Rowland (Carleton)

Pierre Haddad

John Thor Arnason (UofO)

Thank you!

“Further reading”

• Pain Pus & Poison

• http://tvo.org/video/203345/pain-pus-and-poison-episode-1-

pain

• How to grow a planet

• http://tvo.org/program/177589/how-to-grow-a-planet

• Awesome series!

• Poisonous plants database

• http://www.ansci.cornell.edu/plants/