Which phytohormone forms the association between roots and microbes?
Show Hint
Strigolactones are dual-purpose molecules: they act internally as hormones to inhibit shoot branching, and externally as rhizosphere signals to recruit symbiotic mycorrhizal fungi.
Step 1: Understanding the Concept:
Plants release chemical signals into the soil (rhizosphere) to communicate with their surrounding environment.
These signals can recruit beneficial microorganisms or mediate symbiotic relationships that help the plant absorb nutrients. Step 2: Detailed Explanation:
Let us analyze the role of the phytohormones listed:
- Gibberellins, Auxins, and Brassinosteroids: These are primary growth-promoting hormones that regulate internal plant development, cell division, and elongation. They do not act as the primary signaling molecules released into the soil to establish mycorrhizal associations.
- Strigolactones: These are a class of plant hormones produced in the roots and released into the rhizosphere.
- They act as crucial chemical signals that attract and promote the symbiotic association between plant roots and arbuscular mycorrhizal (AM) fungi.
- When AM fungi detect strigolactones in the soil, they begin branching toward the root to establish a symbiotic relationship, which helps the plant absorb phosphorus and other minerals.
- (Note: Strigolactones also act as germination stimulants for parasitic weeds like Striga and Orobanche, which detect this signal to find host plant roots).
Therefore, strigolactones are the phytohormones responsible for establishing the association between plant roots and beneficial soil microbes. Step 3: Final Answer:
The correct option is (D).
