CYTOCHALASIN-D DOES NOT INHIBIT GRAVITROPISM IN ROOTS

It is generally thought that sedimenting plastids are responsible for gravity sensing in higher plants. We directly tested the model generat ed by the current statolith hypothesis that the gravity sensing that l eads to gravitropism results from an interaction between the plastids and actin microfilaments. We find that the primary roots of rice, corn , and cress undergo normal gravitropism and growth even when exposed t o cytochalasin D, a disrupter of actin microfilaments. These results i ndicate that an interaction between amyloplasts and the actin cytoskel eton is not critical for gravity sensing in higher plants and weaken t he current statolith hypothesis.