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45 Cards in this Set

  • Front
  • Back
What is a herbicide?
a chemical used for plant control that can be selective or non-selective
What the 4 ways herbicides can be classified?
1) chemistry
2) cropping pattern- agronomic, etc.
3) weed spectrum
4) mode-of-action
What are the 7 mode-of-actions for herbicides?
1) photosynthetic inhibition
2) amino acid inhibition
3) growth inhibition (mitotic)
4) pigment inhibition
5) cell membrane disruptors
6) growth regulation
7) fatty acid/lipid synthesis
What are the 4 types of selectivity?
1) placement
2) uptake
3) metabolism
4) differential binding
What are the sequence of events from herbicide plant entry to plant death?
entry into plant --> entry into individual cells --> metabolism --> translocation --> entry into subcellular organelles --> interaction with target site --> death
What are the 7 companies that create herbicides?
1) Mosanto
3) Bayer
4) Dupont
5) Dow
6) Valent
7) Syngenta
How were the first herbicides discovered?
- spray and pray
- spray and look
- spray and rate
they used whole plants (1 dicot and 1 grass)
two rates, PRE and POST
used a single molecule
What are the (dis)advantages of whole plant analysis (Arabidopsis)?
Adv: hard to miss activity
Disadv: slow, lot of work, $$$
How does whole plant analysis work?
- trend towards mixture of compounds
- solution dunking of plants (Arabidopsis)
What can in vitro assay of algae be used for?
cell count, chlorophyll analysis, O2 evolution
What are the (dis)advantages of using algae for herbicide testing?
Adv: can reuse culture, can accumulate lipophilic compounds for env. fate and monitoring
Disadv: cannot detect all herbicides
What are 3 types of in vitro assays?
1) algae
2) heterotrophic higher plants
3) photoautotrophic higher plants
What are 2 tests used to screen for new MOAs?
2) gene expression profile
What is QSAR?
"Quantitative Structure Activity Relationships"
- allows you to fine tune activity or other desired trait
- it is able to correlate mathemathically the chemical activity in a biological system
What tests are used during QSAR?
1) octanol/H2O partitioning
2) pKa- for weak acid in phloem
3) electronic (charge)
What is mode-of-action and mechanism of action?
Mode- symptoms that occur after herbicide application leading to death
Mechanism- the actual biochemical site that the herbicide affects
How does a surfactant affect an herbicide droplet?
reduces surface tension and increases spread of droplet
What characteristics affect droplet drift?
- nozzle type, size, pressure
- evaporation
- wind speed
- canopy characteristics (boundary layer)
What characteristics affect vapor drift?
- temp
- humidity
- air speed
- volatility (more when wet)
What does the Freudlich equation tell you?
how much herbicide is tied up in the soil
What is influences the amount of herbicide adsorbed?
- nature of soil (pH)
- nature of herbicide
- water in soil
What influences the degradation of herbicide?
- chemical
- microbial activity
- photodecomposition
What is pKa?
The pH where the weak acid herbicide is in equal amounts of neutral and charged form
When applying herbicide in the ground for root absorption, why is applying a lot futile?
roots can only reach a certain concentration
What is the RCF?
Root Concentration Factor
- Herb in root tissue/Herb in bathing soln
What types of herbicides cause the roots to be the most concentrated?
Lipophilic and low pH (weak acids)
Explain how weak acids can get into foliar tissues.
Goes from lipophilic as a charged particle to hydrophilic since cell wall is acidified so it becomes neutral, passes through and charged at other side
What type of leaves absorb the most herbicide?
young leaves with less waxes and less trichomes take up more
What factors affect foliar uptake?
- chemical and physical nature of cuticle
- nature of herb/surfactant
- environment at leaf cuticle development
- environment at time of leaf absorption
What environmental conditions most affect leaf absorption?
- warm, humid, cloudy
What are the functions of the cuticle?
- prevents water loss
- barrier to diseases
- shield UV light
What are the components of the cuticle?
- epicuticular waxes
- cutin framework
- cuticular waxes
pectin and cellulose carbohydrate polymers
What is movement across the cuticle dependent on?
- partitioning into the cuticular membrane
- diffusion across the cuticular membrane
- partitioning into apoplasm
What type of diffusion is movement across the cuticle?
What are problems with using models to predict herb movement across the cuticle?
Studies indicate that it is not correlated with wax removal or cuticle thickness but more correlated with soluble lipids, herb proportion and overall cuticle membrane composition
What will drive herbicides getting into cuticle?
- contact angle (spread across top)
- cutinized layer and ability to travel through
What factors influence absorption/movement and the effect?
high temp
- sometimes no effect
- increase membrane fluidity
- inc metabolic activity, more removal
high relative humidity
- herb droplet retains more water, less likely to crystallize
- hydrophilic pores swell
What affects herb uptake into plant cells?
- weak acids are more permeable in undissociated form
How are herbicides translocated short distances?
cell to cell diffusion through plsmadesmata or free space
How is translocation studied and what is the (dis)advantages?
extensive use of radioactive C
Adv: no cleanup, extraction, separation (more samples at once)
Disadv: cannot discern btwn parent molecule and metabolites
What are the 3 active sites in phloem translocation?
loading, unloading, maintaining gradient
In herbicide-phloem movement, is herbicide flow a complete match with sucrose and why is this desirable?
No, b/c direct flow with sugar may actually miss some sites
How does herb translocate in xylem?
high water potential in soil, low in atmosphere correlating with transpiration rate
Where does xylem translocated herbicides accumulate in the plant tissue?
leaf tips, margins
What processes are used in herbicide metabolism?
conversion using hydrolysis, oxidation, oxygenation, hydroxylation or reduction, and conjugation