L3 - Herbicide Tolerance Flashcards
define weed
plant growing in the wrong place at the wrong time
Weeds contribute to what losses
loss in production 13.2% $76bn
What quantitative damage do weeds cause
due to competition with water, light and nutrients, and to antagonism (parasitism and allelopathy)
What qualitative damage do weeds cause
indirect damage due to crop yield reduction, contamination of seeds, slowing of tillage and harvesting practices, and degradation of quality of milk or other animal products
How can weeds be controlled
• Herbicides: but heavy usage has lead to groundwater contamination, death of wildlife species, human/animal illnesses
(Also farmers have to use both broad-spectrum herbicides (before planting) and several narrow-spectrum herbicides (during crop growth))
- Tillage: leaves valuable topsoil exposed to wind and water erosion
- Hand weeding: Very labour intensive, not suitable for large scale
Herbicides contribute how much of the pesticide market
45%
$33bn
N. America has the greatest sales of pesticides T/F
T - 27% of the market
Whats the most common herbicide, whats its LD50 value
Glyphosate
LD50 301 for humans - low mammalian toxicity
(lower the value the more toxic)
What mode of action is taken on grasses and dicots, Roundup is an example of this mode.
•EPSPS inhibitors (grasses & dicots): The enzyme EPSPS is used in the synthesis of the amino acids tryptophan, phenylalanine & tyrosine.
Glyphosate (Roundup) is a systemic EPSPS inhibitor inactivated by soil contact
What are ACCase inhibitors
•ACCase inhibitors (kill grasses): Acetyl coenzyme A carboxylase (ACCase) is part of the first step of lipid synthesis. Thus, ACCase inhibitors affect cell membrane production in the plant meristems
What are ALS inhibitors
•ALS inhibitors (grasses & dicots): The acetolactate synthase (ALS) enzyme is the first step in the synthesis of the branched-chain amino acids (valine, leucine, isoleucine) eventually leading to inhibition of protein synthesis
How do synthetic auxins work?
mimic this plant hormone. They have several points of action on the cell membrane, and are effective in the control of dicot plants. E.g. 2, 4-D
Discuss Photosystem II inhibitors mode of action
reduce e- flow from water to NADPH2+ at the photochemical step in photosynthesis. Cause electrons to accumulate on chlorophyl molecules -> increased oxidation -> death
Discuss Photosystem I inhibitors mode of action
steal e- from the normal pathway through FeS – Fdx – NADP leading to direct discharge of electrons on oxygen
- > reactive oxygen species
- > high levels of oxidation
- > plant death
List all the modes of action - herbicides
- EPSPS inhibitors
- ACCase inhibitors
- ALS inhibitors
- Synthetic auxins
- Photosystem II inhibitors
- Photosystem I inhibitors
