Glutathione-S-transferase is responsible for the selectivity of
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Remember:
- Triazines (Atrazine) \(\rightarrow\) Detoxified by Glutathione-S-transferase (GST).
- Sulfonylureas (Metsulfuron) \(\rightarrow\) Detoxified by Cytochrome P450.
This distinction is a common topic in herbicide physiology exams.
Step 1: Understanding the Concept:
Selectivity is a fundamental property of herbicides that allows them to kill target weeds without injuring the crop.
This selectivity is often mediated by the plant's endogenous biochemical pathways, which can rapidly metabolize and detoxify the active herbicide molecules. Step 2: Detailed Explanation:
Let us analyze the role of the enzyme Glutathione-S-transferase (GST):
- GST is a major family of detoxification enzymes found in plants.
- It catalyzes the conjugation of triazine herbicides (such as atrazine) with reduced glutathione (GSH).
- This conjugation reaction attaches a hydrophilic glutathione molecule to the electrophilic site of the herbicide, rendering the herbicide completely inactive and non-toxic to the plant.
- Tolerant crop plants, such as maize (Zea mays), possess exceptionally high levels of active GST enzymes, allowing them to rapidly detoxify triazines.
- Susceptible weed species lack sufficient levels of these specific GST enzymes, which leads to toxic accumulations of the herbicide and subsequent cell death.
- While other enzymes like cytochrome P450 monooxygenases are involved in the metabolism of sulfonylureas and phenylureas, GST is primarily responsible for the natural selectivity shown by crops towards the triazine family of herbicides. Step 3: Final Answer:
The correct option is (D).
