Analysis on the relocation movement of chloroplasts in fern and moss cells

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Mechanisms of chloroplast relocation movement induced by light and mechanical stimuli were analyzed in fern and moss cells.Contribution of Ca^<2+> in the signal transduction of these responses was analyzed by changing the Ca^<2+> concentration of external media and by application of Ca^<2+> transport inhibitors (La^<3+>, Gd^<3+>). In both fern and moss cells, influx of Ca^<2+> from the external source was found to be essential in mechano-induced chloroplast relocation but not in the light-induced one, showing the different role of Ca^<2+> in the signal transduction of mechano- and light-induced responses.GFP-tubulin and GFP-talin genes were introduced to moss cells and stable transformants were obtained. In the transformants, intracellular architecture of actin filaments and of microtubules in the live cells was easily observed under fluorescence microscope. During and after photorelocation movement, tight association of microtubules to the chloroplasts was noticed. Reorganization of actin filaments was also observed during photorelocation movement. Reticulate actin structure appeared around the place of chloroplast accumulation. These results indicate the significant roles of both cytoskeletons in the chloroplast relocation movement. In fern cells, these GFP-fusion constructs did not work. However, by changing the fluorescent label, we succeeded in the visualization of actin filaments in live fern cells.