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CHANGES IN MICROTUBULE DISTRIBUTION IN GRAVISTIMULATED CAULONEMAL TIP CELLS OF THE MOSS PHYSCOMITRELLA PATENS.  P. Chattaraj, E. Johannes and N.S. Allen. Department of Botany, North Carolina State University, NC.

   Cytoskeletal elements play an important role in the early steps of gravity signaling [Kiss. (2000) Crit Rev Plant Sci 19: 551-573]. Whereas higher plants are likely to use actin filaments to sense changes in the gravity vector, microtubules appear to have a dominant role in mosses [Schwuchow et al. (1990) Protoplasma 159:60-69]. In this study, we use the moss Physcomitrella patens as a model system to investigate microtubules dynamics following gravistimulation. The tip-growing apical cells of dark-grown caulonemal filaments of P. patens respond to gravity with upward growth. Six-day-old filaments were embedded in low melting point agarose under dim green light and allowed to recover in darkness overnight. Filaments were then rotated 90° and microtubule distribution in the tip cells was monitored over time by indirect immunofluorescence microscopy. Microtubules accumulated on the lower flank of the tip cell 30 minutes after gravistimulation. This implies that microtubules are involved in gravity perception and early signal transduction in P. patens.

(Supported by NASA grant NAGW 4984.)

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