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AllelopathAllelopathyy

• chemical interactions between (higher) plants• chemically mediated fight of plants for nutritives • allelopathic compounds (toxins) - secondary

metabolites, structurally simple – terpenes or aromatics

• allelopathy is common in trees and bushes, plants in desert (lack of water and nutritives)

• exists in all climatic zones

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AllelopathAllelopathyybest known example: Eastern Black walnutEastern Black walnut (Juglans nigra) and Common walnutCommon walnut (Juglans regia) – plants under tree wilt and die to the distance of tree roots

OH

OGlcOH

O

OOH

1. hydrolýza

2. oxidace

juglone

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JJuglonuglonee• water-soluble brown pigment• bound in glycoside• present in roots, leaves and green peel

of nuts• detectable in depth of 8 m

and distance 27 m from tree trunk• toxic against other plants• inhibits seed germination (100 %

inhibition in letuce at a dose 0,002 %)• some plants tolerate allelopathic

toxins

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AllelopathAllelopathyy Other examples – desert bushes

O

O

O

3-acetyl-6-methoxy-benzaldehyd

COOH

E-cinnamic acid

• Toxins are produced in leaves; fallen leaves decompose and release toxins in soil; persistent

• Bush of the genus Parthenium (Asteraceae): its toxin (E- cinnamic acid) has allelopathic effect to the plant itself.

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AllelopathAllelopathyy • zones of bushes in South California• dominating Salvia and Artemisia• thorny, low bushes, no vegetation in the vicinity despite

a suitable climate• allelopathic toxins - terpenes

OO

1,8-cineol camphor

Periodic natural cycle:• repeated fires (25 years interval )• 2 years after the fire, annual plants

dominate• in 3-4 years, thorny bushes start

to grow and spread• in 5-7 years, the bushes dominate,

contaminate soil with terpenes and “kill” neighbouring plants

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Other compounds produced by plants, inhibiting Other compounds produced by plants, inhibiting seed germination or plant growthseed germination or plant growth

HO

O

HO

S S S

ON

N

NN

O

salicylic acidoak (Quercus) caffeine

• autotoxic effect• probably autoregulation

of plant density • natural changing

of vegetations at a locality• sustenance of biodiversity

α-terthienylAfrican marigold (Tagetes)

Allelopathic toxins can be a model for synthetic herbicides. Allelopathic toxins can be a model for synthetic herbicides.

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Synthetic herbicidesSynthetic herbicides • The mechanism of effect of allelopatic allelopatic

compounds compounds has not yet been studied in detail. Thus, they are not investigated as possible natural templates for herbicides.

• Effect of synthetic herbicides – often manipulation with fytohormonesfytohormones and their synthetic analogs.

• Classification of herbicides: generalgeneral

selectiveselective• Other classification: contactcontact

systemicsystemic

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Structural typesStructural types

• inorganicinorganic – sodium chlorate (Travex); general herbicide

• organicorganic – main groups:

• Chlorinated carboxylic acids Chlorinated carboxylic acids – for monocotyledons (grasses); t.e.x. trichloacetic acid (TCA)

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• phenoxyalkancarboxylic acidsphenoxyalkancarboxylic acidsherbicides derived from plant growth regulators

Structural typesStructural types

R = CH3, 2-methyl-4-chlorophenoxyacetic acid (MCPA)

R = Cl, 2,4-dichlorophenoxyacetic acid (2,4-DCPA)

Cl

R

O COOH

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• DDerivatives of carbonic acid erivatives of carbonic acid - carbamatesand thiocarbamates – for monocotyledons, use as pre-emergent herbicides (before seed germination)

• DDerivatives of urea erivatives of urea - inhibit photosynthesis

HNCOOCH3

OHN

CH3OS

HN

O

HN N

O

Cl

Cl

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• heterocyclic compounds heterocyclic compounds - triazines, triazols, diazines; inhibit photosynthesis

• OOther structural types ther structural types - anilides, nitriles, phosphonates, phenols

COOCH3

SHN

HN

ON

NN

OO HN N

NN

Cl

NH

NN

NH

NH2

P

HO

HO

O

NH

COOH

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InteraInteractionction host-para host-parassitite in highere in higher plantsplants

• Parasites in higher plants - mistletoe, dodder (on branches), Striga (on roots).

• Seed of a parasitic plant must 1) germinate near the host, 2) connect to the host tissue. Parasite responds to root exudates of the host plant.

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• Striga – parasite on sorghum roots (African cereal grown for sweet syrup)

OCH3H3C

OH

H

OH

O

OH

CH3

O

O

O

OO

strigolstrigol, signal 1)stimulates seed germination of parasitic plant

dimethoxybenzodimethoxybenzoququinoninonee, signal 2)

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PhyPhytoalexintoalexinss a andnd phphytotoxinytotoxinss

• interaction between plants and microorganisms (earlier between higher and lower plants)

• wild plant species are usually naturally resistant to diseases caused by microorganisms

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Classification of factors causing Classification of factors causing plant resistance to diseasesplant resistance to diseases

• Before microorganism attack:Before microorganism attack:• prohibitinsprohibitins – inhibit multiplication of microorganism• inhibitinsinhibitins - toxic to microorganism

• After microorganism attack:After microorganism attack:• post-inhibitinspost-inhibitins – formed from precursors present

in plant constitutively• phytoalexinsphytoalexins - synthesised de novo by gene

expression or by activation of latent enzymatic system

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HO

HO

catecholcatechol, , prohibitinprohibitin from resistant onion varieties

• structural base of anthocyanins present in many plants and having fungicidal effect

• isoflavonoids and flavonoids are efficient fungicides; they occur e.g. in plants of the genus Lupinus

N

O

O

H3CO

OCH3

berberinberberinMahonia aquifolium

roots

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• post-inhibitins post-inhibitins are often glycosides, the toxin may be released by hydrolysis, or hydroquinones, oxidised enzymatically to toxic quinones

CN

SSGlc

NOSO3

enzyme+ Glc + HSO4

sinigrinesinigrine allylisothiocyanateallylisothiocyanate(glucosinolate)

allylisothiocyanate is highly toxic to pathogenic fungi

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AfterAfter mi miccroorganismroorganism attack attack• phytoalexinsphytoalexins – most important and best studied

phase of plant defence from microorganisms• phytosphytos = plant, alexosalexos = heal the disease

• PhytoalexinsPhytoalexins are produced are produced de novode novo to defend to defend from disease; response of a plant to micro-from disease; response of a plant to micro-organism attack.organism attack.

• Difference between phytoalexins and plant Difference between phytoalexins and plant toxinstoxins:

• toxins are constitutive (produced in plant all the time)

• phytoalexins are induced (response to pathogen)

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• PhytoalexinsPhytoalexins are to smaller extent formed in response to bacteria or virus attack or to abiotic stress (UV light, heat shock, wound, high concentration of salts in soil)

• Phytoalexins Phytoalexins can becan be natural natural modelmodelss forfor synt synthhetic fungicidetic fungicideses..

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Examples ofExamples of phphytoalexinytoalexinss

O

O

O

HO

CH3

CH3

O

OO

phaseollinphaseollin, first phytoalexin identified; common bean (Phaseollus vulgaris)

ipomeamaronipomeamaron (sweet potatoes)

HO

HO

rishitinrishitin(potatoes, Solanum tuberosum)

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Examples ofExamples of phphytoalexinytoalexinss

O

HO benzobenzoic acidic acid, defence from decay of apples; preservative in food industry

OH

HO

OH

resveratrolresveratrol, phytoalexin of several plant species, present in red wine

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Synthetic fungicidesSynthetic fungicides

Classification (effect): contact

systemic

Classification (structure): inorganic

organic

• Inorganic fungicidesInorganic fungicides – compounds containing sulfur, copper, quicksilver, zink, tin, or baryum

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• Organic fungicidesOrganic fungicides

• dithiocarbamates, chlorinated aromatic compounds, anilin derivatives, aromatic nitrocompounds (contactcontact)

• benzimidazoles, pyrimidines, piperazines, derivatives of morfoline or triazol (systemicsystemic)

N

NNH

O

NHCOOCH3N

H

N

S

N

BenomylBenomyl ThiabendazolThiabendazol

Natural benzoxazinones were isolated from some grass species.

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PhPhytotoxinytotoxinss / pathotoxin / pathotoxinss

• After pathogen attack, some microorganisms produce secondary compounds that are toxic to the plant (symptoms of a plant disease).

• PathotoxinsPathotoxins are microbial metabolites causing pathological changes (symptoms) in the host plant.

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PathotoxinPathotoxinss - typ - typeses of compoundsof compounds

• low-molecular (aromatics) – influence plant growth (plant wilt)

• high-molecular (peptides, proteins) – cause plant necrosis, decay of tissues

OH

COOH

HO

O

toxin from pathogenic fungus Ceratocystis, causing elm wilt (transmitted by bark beetles – genus Scolytus)

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Gibberellins Gibberellins

• Discovered in fifties• Known as pathotoxins from Gibberella (on rice) -

the "foolish seedling" disease in rice• extreme stem elongation that weakens the plant• first isolated in 1935 from fungal strains

(Gibberella fujikuroi)

H

O

CO

COOHHO

H

OH

Gibberellic Gibberellic acidacid, ,

gibberellin gibberellin AA33

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GibberellinsGibberellins• Pathotoxins that influence plant hormonal system,

the wilt is caused by unnatural hormone levels.• Later a big group of diterpenes with ent-gibberellane skeleton was

discovered in plants and their hormonal function explained.

H

H

entent-gibberellane skelet-gibberellane skeletononNowadays about 90 compounds of this type and effect known (19 or 20 carbon atoms)

GibberellinsGibberellins are formed in all plant organs. The highest concentrations were detected in places of active growth.

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Victorin – the most effectiveVictorin – the most effective pathotoxin pathotoxin knownknown

• disease of oat (Cochliobolus victoriae)• vivicctorintorin is effective at dilution 1:106

• tissues affected by fungus decay (decompose) - cells are fragmented and the tissue looses mechanical hardness (decayed fruits)

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• Pathotoxins of some microorganisms have fungicidal effect on other mikroorganisms (e.g. fungus Epichloe typhina growing on grasses. Its pathotoxins (sesquiterpenes) „force out“ other fungi parasiting on the grass.

• SomeSome pathotoxin pathotoxinss can be naturalcan be natural model model forfor synt synthhetic fungicidetic fungicideses oror remediesremedies..