Answer: They are lipochitooligosaccharides that signal root hair curling and initiation of nodule development in host plant.
- A They act as broad-spectrum antimicrobial compounds that suppress competing pathogens living in the surrounding soil community
- B They are lipochitooligosaccharides that signal root hair curling and initiation of nodule development in host plant
- C They directly catalyze the fixation of atmospheric nitrogen gas into ammonia within the surrounding soil itself
- D They function as antibiotic compounds that protect the host legume's root tissue from fungal infection over time
Correct answer: B. They are lipochitooligosaccharides that signal root hair curling and initiation of nodule development in host plant
Explanation: Nod (nodulation) factors are lipochitin oligosaccharides secreted by Rhizobium in response to flavonoids from legume roots. They bind specific receptors on root hair cells, triggering root hair curling, infection thread formation, and initiation of the nodulation developmental program.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.