Unit 7 Allelochemicals Flashcards
- What is hormesis and what a hermetic response will look like on a graph?
When compounds are more toxic at lower doses, LD50 graph will have a peak at lower doses and become closer to 0 as dose increases.
- What is the effect of chain length and fatty acids saturation on algicide efficacy?
Degree of unsaturation in structures caused greater algal toxicities –> more unsaturated linkages in fatty acid caused stronger algal growth inhibition.
- Short carbon chain –> greater algal growth inhibition effects
- Odd carbon chain –> greater algal growth inhibition effects
- What are the 4 categories of effective algicides?
N-containing compounds, Fatty acids/ esters, terpenoids and derivatives, polyphenolics
- Allelochemicals vs Allelopathic compounds
- Allelochemicals - substance produced by plants, microbes and some animals that function for communication and chemical signaling, fighting off enemies.
- Allelopathic chemicals in contrast, are the compounds that produce detrimental physiological effects on individuals of another species. Made primarily by plants.
-They are considered natural toxins, provide selective advantage, and have evolved to be hazardous to certain competitors. - generally safe bc natural properties, might be as / more toxic than pollutants
- Growing a crop, using a plant to grow interesting chemical, harvesting to purify out of the plant. There is a chemical you haven’t seen before being produced, plants are dying – what could the chemical be? Why are the plants dying?
Production of allelochemicals, upregulated because of environmental conditions. Something the plant is responding to –> Elicitor by microbial attack. Soil may have microbes that the plant is producing a defense against. Provide a specific defense against surroundings.
- What site does juglone, and atrazine bind to?
Inhibits photosystem II by binding to the plastoquinone site – competitively inhibits photosynthesis – Juglone inhibits electron transport.
Atrazine (herbicide) acts at same site as juglone
Plants will be example for study. Where in plant can we find allelochemical?
They are found in all parts of the plant including leaves, roots, fruit as well as in decay of plants – leaf litter
Examples of allelopathic responses
a. Plants exude insect repellants.
b. Phytoalexins – Pathogens against fungi and bacteria.
c. Herbicides for competition
exude - discharge slowly and steadily
General method for purification and characterization of allelopathic chemicals:
Extract from tissue with appropriate solvent – H2O or MeOH or Acetone etc.
Partial purification – Usually chromatography
Test fractions on target organism
Further purify fractions according to activity
Test “pure” compounds – identify compound with activity
Some examples
Name and natural source
- Camphor, Salvia shrubs
- Acetic acid, decomposing straw
- Cinnamic acid, guayule plants
- Juglone, black walnuts tree
- Psoralen, psoralea plants
straw - dried stalks of grain
Mechanisms of Action
- mechanisms can not be simply generalized because of the variety of compounds.
- trying to identify mechanisms can help in the design of useful chemicals
identification procedure is difficult because they have many active sites, making them hard to differentiate primary vs secondary effects
Effects of allelopathic chemicals
*inhibit nutrient uptake (phosphate), K+ uptake
*inhibit plant hormones, inhibit protein synthesis, increase membrane permeability
*Especially cause tonoplast leakage (vacuoles of plants lose water)
*Wide range or effects; probably, general membrane damage is the main cause
Mechanism of Action - Juglone
In many natural products as natural herbicide, made in black walnut tree
- Inhibits photosystem II - by binding to plastoquinone site, as it has similar structure to it. Results in competitive inhibition of photosynthesis.
** This causes disruption of electron transport chain ** - Inhibits CoQ reduction in the mitochondria
Atrazine - also herbicie- act at same site in photosystem II
Why to use allelochemicals as algicides?
- Environment friendly - low toxicity, very selective and Biodegradable
- Potential for controlling harmful algal blooms (HABs)
- Several identified e.g., pyrogallol, hexanoic acid, berberine
Allelochemicals as Algicides
What types of allelocheicals are used for inhibiting microalgae cells?
a. Polyphenolics and their derivatives
b. N-containing compounds
c. Fatty acids/esters
d. Terpenoids and their derivatives
Allelochemicals as Algicides
What are the most common Allelochemical used for HAB control?
HAB - harmful algal blooms
a. Polyphenolics and their derivatives
because they are very efficient in inhibiting microalgae cells
Ex. such as PHBA from Nelumbo nucifera (lotus) and salicylic acid from Oryza sativa (Asian rice) strongly inhibited the growth of Microcystis aeruginosa.
What are fatty acids / esters?
Carboxylic acids possessing long aliphatic chain
Open-chain compounds that contain no rings are aliphatic, whether they contain single, double, or triple bonds. In other words, they may be saturated or unsaturated (>1 double ound).
Fatty acids/ esters as algicides
- Inhibitory effect at temperatures less than 35 ℃
- Degree of unsaturation in structures caused greater toxicity towards alga i.e., more unsaturated linkages in fatty acid caused stronger algal growth inhibition
Short carbon chain –> greater algal growth inhibition effects
Odd carbon chain –> greater algal growth inhibition effects
Which allelochemical type has the weakes effec against HAB?
HAB - harmful algal blooms
Terpenoids and derivaties.
examples are - β-Ionone, eucalyptol, β-cyclocitral, linalool and α-terpineol
N-containing compounds
These can be alkaloids, anilines, aa, and derivatires
Allelochemicals as algicides
What effects do allelochemicals have as algicides?
On photosynthesis
Allelochemicals as algicides
§ Causes abnormality of involved pigments, protein complex and electrons
§ Triggers expression changes of genes associated with
photosynthesis
§ Represses synthesis of core-proteins
On photosynthesis
What are the effects of allelochemicals as algicides on redox balance?
Excessive increase in intracellular ROS
Loss of membrane integrity, cytoplasm leakage, necrotic-like cell death
-there are differen end point
How are the HAB developed?
Naturally and synthesized
Examples of mechanisms of allelochemicals as insecticides - Define effect on the insects
- Repellents - orient insect away from the plant
- Supressants - inhibit biting or piercing
- Locomotor excitants - speed up movement
- Arrestant - immobilizes the insect
- Deterrents - avoids feeding or oviposition
