Wayne R, Staves MP.

Plant Physiol. 1993 May; 102: 16.

Section of Plant Biology, Cornell University, Ithaca, NY 14853.

When an internodal cell of Chara is oriented vertically, the cytoplasm streams down 10% faster than it streams up (1). However, when the cells are treated with various impermeant proteases that act at the plasma membrane-extracellular matrix junction, gravisensing is inhibited even though streaming continues. The gravireceptor is sensitive to Proteinase K, thermolysin and collagenase, but not to trypsin, alpha-chymotrypsin or carboxypeptidase B. Moreover, the tetrapeptide RGDS inhibits gravisensing in a concentration-dependent manner, indicating that the gravireceptor may be an integrin-like protein. Through localized treatments, we have determined that the gravireceptor protein is localized at the ends of the cell (2). Further evidence that the gravireceptor is localized at the plasma membrane-extracellular matrix junctions at the ends of the cell comes from the observation that a unidirectionally-applied hydrostatic pressure (490 Pa) mimics the effect of gravity in inducing a polarity of cytoplasmic streaming. The pressure-induced polarity has identical requirements and sensitivities to inhibitors as the gravity-induced polarity (3). Lastly, the magnitude and the sign of the graviresponse is modulated by the external [Ca2+]. The Ca2+ required for gravisensing appears to enter the cell through two classes of channels that are localized at the ends of the cells. Each one is pharmacologically distinct from the class of Ca2+ channels that is involved in E-C coupling and is localized along the flanks of the cell. We have not yet determined the relationship between the gravireceptor protein and the channels. 1. Wayne et al. (1990) Protoplasma 155, 43-57; 2. Wayne et al. (1992) J. Cell Sci. 101, 611-623; 3. Staves et al. (1992) Protoplasma 168, 141-152

Publication Types:

• Meeting Abstracts

Keywords:

• Cell Membrane
• Cell-Matrix Junctions
• Chara
• Cytoplasmic Streaming
• Extracellular Matrix
• Extracellular Matrix Proteins
• Gravitation
• Gravity Perception
• Hydrostatic Pressure
• NASA Discipline Number 40-50
• NASA Discipline Plant Biology
• NASA Program Space Biology
• Non-NASA Center

Other ID:

• 95607651

UI: 102212620

From Meeting Abstracts