Statolith positioning by microfilaments in Chara rhizoids and protonemata

Area of Science:

• Plant Biology
• Cell Biology
• Gravitational Biology

Background:

• Rhizoids of the green alga Chara are tip-growing cells exhibiting precise positive gravitropism.
• Statoliths in Chara rhizoids maintain a distance from the cell vertex, suggesting a basal force generated by actin-myosin interactions.

Purpose of the Study:

• To investigate the basipetal force acting on statoliths during sedimentation in Chara rhizoids.
• To compare statolith movement in Chara rhizoids with that in protonemata during gravistimulation.
• To elucidate the role of cytoskeleton interactions in statolith movement and gravitropism.

Main Methods:

• Video-microscopy to observe statolith sedimentation and movement.
• Gravistimulation experiments on Chara rhizoids and protonemata.
• Comparison of gravitropic responses in rhizoids and protonemata.

Main Results:

• A basipetal force actively influences statolith movement during sedimentation in Chara rhizoids.
• Statoliths in Chara rhizoids move basipetally, not simply along the gravity vector.
• Chara protonemata, exhibiting negative gravitropism, show tipward statolith transport during gravistimulation.
• Cytoskeleton interactions are crucial for directed statolith movement in both Chara rhizoids and protonemata.

Conclusions:

• Cytoskeleton-mediated statolith movement is essential for gravitropism in tip-growing cells like Chara rhizoids.
• In tip-growing cells, these movements guide statoliths to specific locations for gravitropic response.
• In higher plants, cytoskeleton interactions likely transduce mechanical stress from statoliths to the plasma membrane.