Question

Toxins exuded from the roots of plants into soil are called

• A. Pyrethrins
• B. Repellants
• C. Rotenones
• D. Phytoalexins

Hint:

Phyto (Plant) + Alexin (To ward off/defend).
Think of Phytoalexins as the "Immune System" chemicals of the plant.
When these chemicals affect other plants, the phenomenon is called Allelopathy.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the technical term used to describe chemical substances or toxins released by plant roots into the soil environment, particularly those that function in defense.

Step 2: Detailed Explanation:

• Defining Phytoalexins:
Phytoalexins are antimicrobial and often antioxidative substances synthesized de novo by plants that accumulate rapidly at areas of pathogen infection.
While they are primary internal defense compounds, some are exuded through the roots into the rhizosphere to inhibit soil-borne pathogens or neighboring competing plants.
In a broader context of "Allellopathy," these exuded toxins are often called allelochemicals.

• Analyzing Other Options:
Pyrethrins: These are natural insecticides found primarily in the flowers of Chrysanthemums, not typically exuded by roots as soil toxins.
Repellants: This is a general functional term for any substance that drives away pests, but it is not a specific chemical class or biological term for root exudates.
Rotenones: These are insecticidal compounds obtained from the roots of certain legumes (like Derris species), but they are extracted from the plant tissue rather than being naturally "exuded" into the soil as a regular physiological process.

• Ecological Significance of Root Exudates:
Plants use root exudates to communicate with microbes and defend their territory.
Substances like phenolic acids, flavonoids, and terpenoids can act as toxins against harmful fungi or bacteria in the soil.
This chemical warfare in the soil helps the plant maintain its health and nutrient access.

Step 3: Final Answer:
Among the given scientific terms, Phytoalexins best represents the defense-related compounds associated with plant protection.