ASGSB 1998 Annual Meeting Abstracts

[62]
CELLULAR, MOLECULAR, AND ELECTROPHYSIOLOGICAL CHANGES DUE TO DEVELOPMENTAL POLARITY INDUCED BY GRAVITY IN SINGLE CELLS.    S.J. Roux¹, A. Chatterjee¹, D.J. Eastburn¹, W.M. Hanson¹, M.Porterfield², and P.J. Smith². ¹Dept of Botany, Univ of Texas, Austin, and ²BioCurrents Research Center, Woods Hole, MA.

Ceratopteris richardii is a tropical fern which has become a useful model system for studies of plant growth and development due to the ease with which genetic studies can be carried out on it. We recently reported that in single cell spores of Ceratopteris there is a defined period during which gravity sets a developmental polarity that orients the direction of nuclear migration and subsequent rhizoid emergence. We want to establish the cellular, molecular, and electrophysiological basis for this gravity response. We employed Differential Display Reverse Transcriptase-PCR to find differentially expressed cDNAs during the critical period of gravity responsiveness. We have identified 17 cDNAs by this method, and independently confirmed the differential expression of the mRNAs they encode by Northern analysis. We are currently attempting to clone the full length cDNAs using PCR based methods. In order to assess actin cytoskeletal changes that may occur during polarity fixation, spores were treated with rhodamine-phalloidin and their actin cytoskeleton visualized by confocal laser microscopy at various points during the gravity response window. We are testing whether cytoskeletal changes precede and predict the direction of nuclear migration or occur as a result of that migration. We demonstrated that calcium currents are associated with this process, using a calcium selective electrode to record the net movement of calcium across the membrane of the spore at different locations with respect to the vector of gravity. Results from these cellular, molecular, and electrophysiological analyses will be discussed. (Supported by NASA grants NAGW 1519 & NAG10-0202.)

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