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(P) Biotic Stress: PHYSICAL AND CHEMICAL BARRIERS - Coggle Diagram
(P) Biotic Stress: PHYSICAL AND CHEMICAL BARRIERS
Mutualistic Interactions
Endophytic fungi
e.g. a number of endophytes protect plants against parasites, primarily by production of
alkaloids
Mycorrhyza
root-fungus networks
90 % of vascular plants live in mutualistic symbiosis with soil fungi
fungi provide
increased contact surface of roots for absorption of water and minerals, such as phosphorus, Cu and Zn + digestion of old mycelium (hyphae) provides plants with extra N!
plts provide
photosynthetic carbohydrates and energy
2 major types
Endo
-mycorrhiza - arbuscular mycorrhiza
70% of all plant species
vvvv small :microscope:
no sporocarp (fruiting body)
penetrate cortex cells (intra-cellular)
glomeromycetes (monophyletic group)
Ecto
-mycorrhiza
mostly trees
sporocarp (fruiting body)
outside root + inter-cellular spaces
often basidiomycetes, sometimes asco-
mycetes
present in plant fossils
importance in colonization of (sterile, nutrient poor) land & better growth on poor soils
Lichens
interaction between a fungus (mostly ascomycetes) and photo-autotrophic organisms (cyano- bacteria, green algae, or both)
hyphae use photosynthate and shield their partner against dehydration and high light stress
reproduce w/soredia
absorption of solutes from rain and dew
sensitive bio-indicators of air pollution
pioneer vegetation
Symbiotic N-fixation
plants use NH4+ as a N-source for amino acids and derived compounds
incorporated in plant metabolism by the
GS/GOGAT
pathway
Nitrogen is the main nutrient that limits crop yield! N2 not metabolically accessible
Plants now get their N from 2 sources
The soil
N in reduced form from organic waste (ammonification of soil)
nitrificaiton in well aerated soils –> nitrate
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poorly aerated (anaerobic) soils –> production of N2 gas = de-nitrification
Symbiotic N-fixation
e.g.
Gram-negative bacteria, the Rhizobia, in association with Fabaceae (Leguminosae) :moneybag:
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Gram-positive actinomycetes in association
with diverse dicot species, often trees and shrubs
:evergreen_tree:
Cyanobacteria with diverse dicots, cycads, ferns and mosses :seedling:
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Physical barriers
Protective macro-structures
spines or trichomes (on leaf, shoot and stem)
Protective compound layers
cutin, waxes, and suberin
cutin
3D polyester macromolecule of long-chain fatty acids with ester bonds
the most important component of the
cuticle
: protective layer on the epidermis of all aerial (aboveground) parts of herbaceous plants
wax
a complex
mixture
(not a macromolecule) of extremely hydrophobic
very-long-chain fatty acids
, secreted by epidermal cells through the cell wall
suberin
like cutin, a polyester of hydroxy and epoxy fatty acids
also dicarboxylic acids, phenolic compounds
outer cell walls of all underground organs, cork layers of the periderm, Caspari strips, wound sites
Chemical barriers
3 major groups
Terpenoid compounds
C10: monoterpene, 20: diterpene...
produced by linking C5 components with branched isopentane skeleton (->
isoprene
with 2 double bonds)
number of terpenes have a primary role in growth and development (C G BC C)
cytokinins
isopentenyl group (hemi-terpenes, C5)
gibberellins
di-terpenes, C20
brassinosteroids
derived from tri-terpenes, C30
cell membrane sterols
carotenoids
tetra-terpenes, C40
pigments (red, orange, yellow) for photosynthesis + protection against high light & oxidative stress
carotenoid-derived terpenes
strigolactones :mushroom:
ABA (C15)
protect
against herbivores (toxic/deterrent)
pyrethrins
insecticidal monoterpene
esters
both natural and synthetic (pyrethroids) insecticides
. biodegradable, non-toxic for mammals
axonic poison’: keeps insect neuron membrane Na+ channels open
monoterpenes
conifers such as pines and firs accumulate monoterpenes in needles, twigs and stems (resin)
toxic for insects, including bark beetles
many plants accumulate
essential oils
mix
of
volatile
monoterpenes and sesquiterpenes (C10/15), with characteristic scent and taste :bug: :woman-getting-haircut:
. insect-deterrent effect
often in epidermal glandular hairs
larger
non-volatile
anti-insect herbivore
tri-terpenes
:beetle:
limonoids: bitter tri-terpenes (typically occurring in citrus)
phyto-ecdysones, plant steroids with a similar basic structure as steroid hormones regulating insect / invertebrate development
perturbs moulting and other developmental processes, often lethal . also effective against plant-parasitic nematodes
Tri-terpenes
with activity against
vertebrate
herbivores :<3: 🧼
cardenolides (heart glycosides)
characteristic
lactone
group (ring carboxylic acid)
saponins
Phenolic compounds
very diverse functions (defense, attraction, competition, mechanical support in tissues, UV absorption ...)
most phenolic compounds are synthesized from the aromatic amino acid phenylalanine (shikimate pathway)
Phenylalanine
PAL phenylalanine ammonia lyase
Cinnamic acid
Phenylpropanoids
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important regulatory step
transition from primary to secondary metabolism
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N-containing compounds
mostly synthesized from amino acids
4 important classes:
alkaloids
have a dramatic effect on animal physiology
large family
most contain a heterocyclic ring with N and C and are alkalic, positively
charged (protonated), soluble at cellular pH
typically synthesized from the amino acids tyrosine, tryptophan (aromatic), lysine or from ornithine (intermediate in arginin biosynthesis)
e.g. nicotine, cocaine, Neonicotinoids :bee:
e.g.
Purine
-derived alkaloids: caffeine
Functions
mostly protection against herbivores (toxic, deterrent)
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. Alkaloids are not always produced by the plant itself! (fungal endosymbionts)
cyanogenic glycosides
release of poisonous HCN gas
separated from enzymes in intact tissues!
synthesized only upon damage or herbivory
widespread in grasses, legume species, Rosaceae
a fast-working toxin that inhibits metallo-proteins, such as iron-containing cytochrome oxidase ( = respiration)
a number of herbivores is adapted
glucosinolates
(mustard oil glycosides):
. especially in Brassicaceae (crucifers, mustard family) and related families
also separated from metabolic enzymes in intact tissues
volatile glucosinolate breakdown products > scent and taste of cabbages, broccoli, turnip
. number of herbivores adapted
non-protein amino acids
. can block uptake of protein amino acids
canavanine is incorporated in proteins
non-functional proteins
the plants themselves (e.g. canavalia bean) can discriminate between
the amino acids, similar to a number of adapted insects