Module: | Double Fertilization & Endosperm
Q72: Consider the following statements regarding the role of calcium gradients in pollen tube apical growth:
1. Pollen tube elongation is strictly restricted to the extreme apex, a process heavily regulated by a steep intracellular calcium ion gradient.
2. This calcium gradient is highest at the very tip of the tube, directing the fusion of secretory vesicles to the apical plasma membrane.
3. The trace element Boron acts as a direct antagonist to calcium, actively halting vesicular fusion and terminating tube growth.
Which of the above statements is/are correct?
2. This calcium gradient is highest at the very tip of the tube, directing the fusion of secretory vesicles to the apical plasma membrane.
3. The trace element Boron acts as a direct antagonist to calcium, actively halting vesicular fusion and terminating tube growth.
Which of the above statements is/are correct?
✅ Correct Answer: A
The correct option is A. Statements 1 and 2 are correct, whereas Statement 3 is fundamentally incorrect.
The pollen tube is one of the fastest-growing cells in the plant kingdom, and its structural growth is exclusively localized to its very tip (apical extension). This precise growth is not random; it is causally driven by a steep gradient of cytoplasmic calcium ions (Ca2+), which is highly concentrated right at the apex and drops off further back.
This calcium spike acts as an intracellular signaling mechanism, directing millions of Golgi-derived secretory vesicles (containing pectin and cell wall materials) to fuse exclusively with the apical membrane, pushing the tube forward.
Statement 3 represents a physiological falsehood.
Boron does not antagonize calcium; it works synergistically with it.
Boron forms a chemical complex that stabilizes the newly laid pectin in the cell wall, preventing the rapidly growing tip from bursting under osmotic pressure.
The pollen tube is one of the fastest-growing cells in the plant kingdom, and its structural growth is exclusively localized to its very tip (apical extension). This precise growth is not random; it is causally driven by a steep gradient of cytoplasmic calcium ions (Ca2+), which is highly concentrated right at the apex and drops off further back.
This calcium spike acts as an intracellular signaling mechanism, directing millions of Golgi-derived secretory vesicles (containing pectin and cell wall materials) to fuse exclusively with the apical membrane, pushing the tube forward.
Statement 3 represents a physiological falsehood.
Boron does not antagonize calcium; it works synergistically with it.
Boron forms a chemical complex that stabilizes the newly laid pectin in the cell wall, preventing the rapidly growing tip from bursting under osmotic pressure.