Click here to view Chara rhizoids.

The rhizoids of the alga Chara contraria are 6 to 10 mm long and have barium- and sulfur-containing vesicles which function as statoliths. The living rhizoids on the left were photographed with bright-field optics through a compound microscope. In figure A, the structural polarity of statoliths, localized near the apex, is clear. (The arrow indicates gravity; scale bars= 20 micrometers)

This study investigated the effects of different growth media on the number of statoliths in Chara rhizoids and the resulting response to gravity. This response was quantified by the orientation of the rhizoids with respect to gravity, the time course of curvature, and the overall growth rate.
Extracts of Soil Water (SW) and Artificial Pond Water (APW) constituted the different growth media.

• Soil Water:
  1 L distilled water
  100 g soil (collected in Lubbock, TX)
  1 g agricultural limestone
  
  
• Artificial Pond Water:
  1 mM Hepes (pH 7.0)
  1 mM NaCl
  0.05 mM K₂SO₄
  0.05 mM CaSO₄
  7 mM MgCl₂
  5 mM CaCl₂
  

Kiss determined that Chara rhizoids grown in Soil Water are more responsive to gravity than are those grown in Artificial Pond Water:

There are significantly more statoliths per cell in SW rhizoids (50 to 60; figure B) than in APW statoliths (5 to 10; figure C).

SW rhizoids are uniformly oriented to gravity, whereas APW rhizoids are disoriented.

Click here to view the orientation of Chara plants. In figure B, arrowheads indicate which rhizoids deviate from gravity and asterices indicate rhizoids out of the plane of focus. (The arrow indicates gravity; scale bars= 1 mm.)

Click here to view the time course of curvature in Chara rhizoids.

Therefore, growth media affects the perception and response to gravity.

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