ASGSB 1998 Annual Meeting Abstracts

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GRAVITY INDUCED CALCIUM CURRENTS IN GERMINATING FERN SPORES.  A. Chatterjee¹, M. Porterfield², P.J. Smith², and S.J. Roux¹. ¹Dept of Botany, Univ of Texas, Austin, and ²BioCurrents Research Center, Woods Hole, MA.

Gravity fixes the developmental polarity in germinating spores of Ceratopteris richardii during the first 24 hours after germination is initiated by light. A key objective of our laboratory is to document cellular changes that occur during this period in order to understand the mechanisms by which gravity alters cellular metabolism. As part of our effort to achieve this objective, we used an ion specific microelectrode to measure calcium currents associated with polarity fixation. We found that during the period of polarity fixation, a strong efflux current emerges from the top of the cell, a weaker efflux current occurs at the sides of the cell, and an even weaker influx current enters from the bottom of the cell. This same pattern is reestablished within 5 minutes after rotating the cells 180^o, indicating that turning the cells upside down rapidly reverses the direction of the current. The magnitude difference between the outward current at the top and the inward current at the bottom of the cell is highest in the middle of the polarity fixation period and decreases significantly toward the end of this period. The possible role of this current in gravity-induced polarity fixation will be discussed. This is the first report of a gravity-directed calcium current in single cells. (Supported by NASA grants NAGW 1519 & NAG10-0202.)

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