Herbicide Introduction

Front 1

What is a herbicide?

Back 1

a chemical used for plant control that can be selective or non-selective

Front 2

What the 4 ways herbicides can be classified?

Back 2

1) chemistry
2) cropping pattern- agronomic, etc.
3) weed spectrum
4) mode-of-action

Front 3

What are the 7 mode-of-actions for herbicides?

Back 3

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

Front 4

What are the 4 types of selectivity?

Back 4

1) placement
2) uptake
3) metabolism
4) differential binding

Front 5

What are the sequence of events from herbicide plant entry to plant death?

Back 5

entry into plant --> entry into individual cells --> metabolism --> translocation --> entry into subcellular organelles --> interaction with target site --> death

Front 6

What are the 7 companies that create herbicides?

Back 6

1) Mosanto
2) BASF
3) Bayer
4) Dupont
5) Dow
6) Valent
7) Syngenta

Front 7

How were the first herbicides discovered?

Back 7

- 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

Front 8

What are the (dis)advantages of whole plant analysis (Arabidopsis)?

Back 8

Adv: hard to miss activity
Disadv: slow, lot of work, $$$

Front 9

How does whole plant analysis work?

Back 9

- trend towards mixture of compounds
- solution dunking of plants (Arabidopsis)

Front 10

What can in vitro assay of algae be used for?

Back 10

cell count, chlorophyll analysis, O2 evolution

Front 11

What are the (dis)advantages of using algae for herbicide testing?

Back 11

Adv: can reuse culture, can accumulate lipophilic compounds for env. fate and monitoring
Disadv: cannot detect all herbicides

Front 12

What are 3 types of in vitro assays?

Back 12

1) algae
2) heterotrophic higher plants
3) photoautotrophic higher plants

Front 13

What are 2 tests used to screen for new MOAs?

Back 13

1) HNMR
2) gene expression profile

Front 14

What is QSAR?

Back 14

"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

Front 15

What tests are used during QSAR?

Back 15

1) octanol/H2O partitioning
2) pKa- for weak acid in phloem
3) electronic (charge)

Front 16

What is mode-of-action and mechanism of action?

Back 16

Mode- symptoms that occur after herbicide application leading to death
Mechanism- the actual biochemical site that the herbicide affects

Front 17

How does a surfactant affect an herbicide droplet?

Back 17

reduces surface tension and increases spread of droplet

Front 18

What characteristics affect droplet drift?

Back 18

- nozzle type, size, pressure
- evaporation
- wind speed
- canopy characteristics (boundary layer)

Front 19

What characteristics affect vapor drift?

Back 19

- temp
- humidity
- air speed
- volatility (more when wet)

Front 20

What does the Freudlich equation tell you?

Back 20

how much herbicide is tied up in the soil

Front 21

What is influences the amount of herbicide adsorbed?

Back 21

- nature of soil (pH)
- nature of herbicide
- water in soil

Front 22

What influences the degradation of herbicide?

Back 22

- chemical
- microbial activity
- photodecomposition

Front 23

What is pKa?

Back 23

The pH where the weak acid herbicide is in equal amounts of neutral and charged form

Front 24

When applying herbicide in the ground for root absorption, why is applying a lot futile?

Back 24

roots can only reach a certain concentration

Front 25

What is the RCF?

Back 25

Root Concentration Factor
- Herb in root tissue/Herb in bathing soln

Front 26

What types of herbicides cause the roots to be the most concentrated?

Back 26

Lipophilic and low pH (weak acids)

Front 27

Explain how weak acids can get into foliar tissues.

Back 27

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

Front 28

What type of leaves absorb the most herbicide?

Back 28

young leaves with less waxes and less trichomes take up more

Front 29

What factors affect foliar uptake?

Back 29

- chemical and physical nature of cuticle
- nature of herb/surfactant
- environment at leaf cuticle development
- environment at time of leaf absorption

Front 30

What environmental conditions most affect leaf absorption?

Back 30

- warm, humid, cloudy

Front 31

What are the functions of the cuticle?

Back 31

- prevents water loss
- barrier to diseases
- shield UV light

Front 32

What are the components of the cuticle?

Back 32

- epicuticular waxes
- cutin framework
- cuticular waxes
pectin and cellulose carbohydrate polymers

Front 33

What is movement across the cuticle dependent on?

Back 33

- partitioning into the cuticular membrane
- diffusion across the cuticular membrane
- partitioning into apoplasm

Front 34

What type of diffusion is movement across the cuticle?

Back 34

passive

Front 35

What are problems with using models to predict herb movement across the cuticle?

Back 35

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

Front 36

What will drive herbicides getting into cuticle?

Back 36

- contact angle (spread across top)
- cutinized layer and ability to travel through

Front 37

What factors influence absorption/movement and the effect?

Back 37

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

Front 38

What affects herb uptake into plant cells?

Back 38

plasmalemma
- weak acids are more permeable in undissociated form

Front 39

How are herbicides translocated short distances?

Back 39

cell to cell diffusion through plsmadesmata or free space

Front 40

How is translocation studied and what is the (dis)advantages?

Back 40

extensive use of radioactive C
Adv: no cleanup, extraction, separation (more samples at once)
Disadv: cannot discern btwn parent molecule and metabolites

Front 41

What are the 3 active sites in phloem translocation?

Back 41

loading, unloading, maintaining gradient

Front 42

In herbicide-phloem movement, is herbicide flow a complete match with sucrose and why is this desirable?

Back 42

No, b/c direct flow with sugar may actually miss some sites

Front 43

How does herb translocate in xylem?

Back 43

high water potential in soil, low in atmosphere correlating with transpiration rate

Front 44

Where does xylem translocated herbicides accumulate in the plant tissue?

Back 44

leaf tips, margins

Front 45

What processes are used in herbicide metabolism?

Back 45

conversion using hydrolysis, oxidation, oxygenation, hydroxylation or reduction, and conjugation