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Secondary Plant Metabolism - Coggle Diagram
Secondary Plant Metabolism
secondary products
substances with no direct function in plant growth and development
have limited distribution
major groups:
nitrogen-containing secondary products
most synthesized from amino acids
sources:
aromatic amino acids from shikimic acid pathway
aliphatic amino acids from the tricarboxylic acid pathway
such as....
cyanogenic glycosides
sorghum bicolor
dhurrin
synthesized for Tyr
accumulates in vacuoles of epidermis
degradative enzymes in mesophyll cells
cyanide released upon damage
inactivates metalloproteins
manihot esculenta (cassava)
linamarin, synthesized from Val
Lotaustralin synthesized from Ile
staple food crop (Africa)
grating, grinding, soaking, drying to remove linamarin and lotaustralin
partial paralysis common in consumers
effects of cyanide on cells:
cyanide inhibits metalloproteins
cytochrome oxidase
cyanide-sensitive factor
P450 enzyme
SHOWN ON P67
alkaloids
15000 alkaloids in 20% vascular plants
N part of heterocyclic ring
alkaline pH
protonated at physiological pH
precursors:
amino acids
terpenes
ornithine
roles:
nitrogenous waste
nitrogen storage
growth regulators
defense
most interfere with nervous system
membrane transport
protein synthesis
neurotransmitters
various enzyme activities
major types:
pyrrolizidine
precursor: ornithine
ex: nicotine
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herbivore adaptations to pyrrolizidine:
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tropane
Precursor: ornithine
ex: atropine
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ex: cocaine
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piperdine
precursor: lysine
ex: coniine
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pyrrolizidine
precursor: ornithine
ex: retrosine
quinolizidine
precursor: lysine
ex: lupinine
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isoquinoline
precursor: tyrosine
ex: codeine
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ex: morphine
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indole
precursor: tryptophan
ex: psilocybin
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ex: reserpine
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ex: strychnine
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toxicity
livestock deaths due to lupine, larkspur, groundsel
nearly all are toxic to humans but can be used in medicinal dosage
glycosinolates
brassicacea (cabbage, broccoli, radish)
glucosinolate and enzymes combined if damaged
breakdown products toxic to herbivores
cabbage butterfly resistent
brassica napus genetic engineering
non-protein amino acids
mode of toxicity
block protein synthesis
block amino uptake
mis-incorporation into proteins
canavalia ensiformis (jack bean)
main interests:
human toxicity
medicinal properties
phenolic compounds
Synthesis
Shikimic Acid Pathway
primary pathway in plants
not present in animals
Malonic Acid Pathway
primary pathway in bacteria and fungi
in plants, modifies phenolics produced by PAL pathway
chemically heterogenous group
~10,000 members
organic solvent soluble group
aqueous soluble group
large insoluble polymers
roles
defense
mechanical support
attractants
uv protection
allelopathy
Most plant phenolics are from phenylalanine
phenylalanine ammonia lyase (PAL)
branch point between primary and secondary metabolism
induced by environmental factors
low nutrients
light (phytochrome)
fungal infection
multigene family
tissue-specific
environment-specific
simple phenolic compounds
simple phenylpropanoids
coumarins: phenylpropanoid lactones (cyclic esters)
benzoic acid derivatives
formed by cleavage of 2C unit from side chain
Furanocoumarins
furan ring attached to phenolic compound
phytotoxic
activated by UV-A
intercalate into DNA
binds C'S and T's, blocking transcription and repair systems
abundant in Umbilliferae
celery, parsnip, parsley
increase 100x by stress or disease
causes skin rash
insect adaptations to Umbilliferae
live in silken webs or rolled
uv protectant
Allelopathy
release of phenolics to soil
reduce germination and growth of nearby plants
caffeic acid, ferulic acid from many species
juglone from walnut
soil concentration
biotech thrust
Lignin
second most abundant organic substance in plants
highly branched polymer
covalently binds cellulose and polysaccharides
hydrophobic network
derived from phenylpropanoid alcohols
coniferyl alcohol
coumaryl alcohol
sinapyl alcohol
linkages between aromatic alcohol units
laccases
peroxidases
physiological roles
adds mechanical strength
reduces susceptibility to pathogen attack
reduces digestibility of cell wall
flavonoids
largest class of plant phenolics
derived from shikimate and malonate pathways
groups distinguished by oxidation of C3 bridge
four major groups:
anthocyanins
colored flavanoids that attract animals
most widespread group
glycosidic linkage at position 3
anthocyanidin = no sugar
responsible for red, pink, purple, blue
pigment complexes:
blue pigment of commelia commnis
6 anthocyanins
6 flavones
2 Mg2+
color depends on:
B-ring hydroxyl and methoxyl groups
increased hydroxyl = increased blue
increased methoxyls = increased red
aromatic acids esterified to main skeleton
pH of cell vacuole
flavones
absorbs UV-B
permits visible light to pass
increased UV-B = increased flavonols
arabidopsis chalcone synthase mutants
lack flavonoids
more sensitive to UV-B
mediate N-fixing symbiotic associations; secreted by legume roots
regulate polar auxin transport
flavonols
form nectar guides in flowers
symmetric pattern of stripes, spots, concentric circles
pattern guides insects to flower
bumble bee and black eyed susan
absorb UV radiation
absorb UV-B
permit visible light to pass
increased UV-B = increased flavonols
arabidopsis chalcone synthase mutants
lack flavonoids
more sensitive to UV-B
mediates N-fixing symbiotic associations; secreted by legume roots
regulate polar auxin transport
isoflavones
found mostly in legumes
insecticidal activity (rotenoids)
anti-estrogen activity (sheep and clover)
anti-cancer activity
phytoalexin activity (anti-microbial)
rotenone
powerful insecticide and piscicide
interferes with oxidative phosphorylation
harmless to animals unless in bloodstream
common modifications
hydrophilic enhancements
hydroxyls: 4, 5, 7, and others
glycosidic linkages
hydrophobic enhancements
methyl esters
modified isopentyl units
Tannins
plant phenolic polymers
bind collogen
increased resistance to heat, water, microbes
MW: 600-3,000
categories:
condensed
formed by flavonoid polymerization
woody plants
strong acid hydrolysis to anthocyanidins
large polymers
hydrolyzable
heterogenous polymers
gallic acid
sugars
smaller than condensed tannins
weak acid hydrolysis
act as general toxins
reduce growth in mammals
deer and apes avoid high tannin plants and unripe fruit
humans prefer some tannins (apples, blackberries, tea, red wine)
tannins in red wine
block endothelin-1 formation
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bind proteins in gut
types of bonding:
hydrogen
covalent
result:
inactive digestive enzymes
large aggregates of dietary proteins
rodents and rabbits tolerate tannins
high proline salivary proteins
bind tannins
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terpenes
Synthesis of terpenes
terpenoids formed from isoprene units
derived from isoprene-like molecules
isoprene unit: 5C branched unit
condensation occurs head-to-tail
heat degradation yields isoprene
isopentenyl pyrophosphate (IPP)
synthesized by Mevalonic Acid Pathway
pathway:
operates in cytoplasm
sequential joining of 3-acetyl-CoA
pyrophosphorylation
decarboxylation
dehydration
occurs in cytosol
dimethylallyl pyrophosphate (DMAPP)
synthesized by methylerythriol-P pathway
MEP pathway:
operates in plastids
GAP + 2C from pyruvate
occurs in plastids
MEMORIZE P11--MOST LIKELY SOURCE OF TERPENE SYNTHESIS QUESTIONS
Terpenes in growth and development
gibberellins:
diterpene (C20)
plant hormone
abscisic acid
sesquiterpene (C15)
degradation of 9'-cis-Neoxanthin (C40)
plant hormone
sterols
triterpene (C30) derivatives
stabilize membranes
carotenoids
tetraterpenes (C40)
accessory photosynthetic pigments
photooxidation protection mechanism
provide colors in some organisms
dolichols
long-chain polyterpenes
sugar carriers for cell wall and glycoprotein biosynthesis
waxes (cutin, suberin)
membrane anchors
terpene-derived side chains are hydrophobic and can anchor molecules in membrane
phytol tail of chlorophyll
pyrethins
monoterpene (C10) esters (irregular)
chrysanthemum sp flowers and leaves
used commercially as insecticide
rapidly acts on insect nervous system
pyrethrin I main insecticide
pyrethrin II rapid paralyzing effect
low toxicity to mammals
toxic to fish and amphibians
rapid turnover in environment: air and light sensitive
synthetic pyrethrins
synthetic analogues with improved properties
increased lifetimes (several days)
Cl confers greater stability in air and light
cyano group increases toxicity
greater insect toxicity (>1000 x pyrethrin I)
permethrin and cypermethrin used against skin parasites
regular vs irregular monoterpenes
regular:
head-to-tail coupling
synthesis:
ionization of DMAPP to allylic cation
addition of double bond to IPP
proton loss
irregular:
not head-to-tail coupling
characteristic cyclopropane ring
exclusively found in composite/asteraceae
synthesis:
2 DMAPP joined
terminated by cyclopropane ring formation
Terpenes against Herbivores
terpenes in conifers
toxic to numerous insects
accumulate in resin ducts
Monoterpene (C10) esters (irregular)
in conifers:
accumulate in resin ducts
toxic to numerous insects
increased concentration when attacked
in essential oils:
volatile monoterpenes and sesquiterpenes
characteristic odor of foliage
insect repellent properties
frequently found in glandular hairs
synthesized in hair cell
stored in rounded cap at top
extracellular space formed when cuticle and cell wall pull away
Specific terpenes:
Limoene:
essential oil
uses: flavoring, aromatherapy, perfumery
monoterpene in citrus species
Menthol:
monoterpene in peppermint
essential oil
uses: flavoring, carminative, aromatherapy
Limonoids
non-volatile
active against herbivores
azadirachtin
azadirachta indica (neem tree)
used as commercial insecticide
feeding deterrent >50 ppb
low toxicity to mammals
phytoecdysones:
plant substances with same basic structure as insect molting hormone
first isolated from polypodium vulgare (ferm)
disrupts molting and other developmental processes
Cardenolides:
glycosides that taste bitter and are extremely toxic to vertebrates
act on Na+/K+ -activated ATPases of heart
digitalis sp (foxglove)
Saponins:
steroid andtriterpene glycosides
soap-like properties
lipid soluble = steroid/triterpene
water soluble = sugar
interfere with steroid uptake
disrupt cell membranes
Prey's Perfume:
cuscuta pentagona
obligate parasitic plant
no leaves
poor photosynthesis
seed reserves for one week after germination
taps into phloem of other plants for food
USDA's top ten weed list
tomato (and other plants)
synthesizes potent attractants
colonized by cuscuta pentagona
wheat and other grasses
synthesizes attractants
synthesizes potent repellents
avoided by cuscata pentagona
function:
defense
herbivores
pathogens
structural support
lignin
attractants
pigments
volatile organics
primary vs secondary metabolism
primary:
common to all plants
energy generation
nucleic acid synthesis
amino acid synthesis
protein sythesis
lipid synthesis
secondary:
unique biochemistry
highly variable
phytochemicals
pharmaceuticals
pharmacognosy: study of plant secondary products as pharmaceuticals
nutraceuticals: vitamins, minerals, and other useful compounds that promote wellness
phytoceuticals: plant-derived compounds used as pharmaceuticals
...photosynthesis is in its own class, not under either of these