[Campbell Biology P.910] The text discusses both the statolith hypothesis for gravitropism a... | Practice Question

The text discusses both the statolith hypothesis for gravitropism and evidence from plant mutants. Which statement best summarizes the current understanding based on the provided information?

  • A: Statoliths are absolutely essential for gravitropism in all plants.
  • B: While statoliths enhance gravitational sensing, other cellular mechanisms can also contribute to gravitropism.
  • C: Gravitropism only occurs in the presence of functional statoliths; mutants lacking them cannot sense gravity.
  • D: The statolith hypothesis has been completely disproven by studies on Arabidopsis and tobacco mutants.

Explanation

While the statolith hypothesis proposes a primary mechanism for gravitropism, the text notes that mutants of Arabidopsis and tobacco lacking statoliths are still capable of gravitropism, albeit slower. This suggests that the entire cell, possibly through mechanical pulling on proteins tethering the protoplast and cytoskeleton distortion, can also sense gravity, meaning statoliths enhance, but are not always exclusively required for, gravitational sensing.