A centrin homologue is localised across the developing cell plate in gymnosperms and angiosperms

A homologue of centrin, a calcium-binding protein, has been found in some l and plants and shown by immunochemistry to localise prominently to the cell plate in angiosperms. In the present study, we used immunochemistry to ext end these observations to gymnosperms and to further our understanding of c entrin localisation in the two divisions. In Monterey pine, immunoblotting revealed an 18 kDa centrin homologue. Immunofluorescence confocal microscop y of root-tip cells of pine and onion and three-dimensional reconstruction showed that a centrin homologue is localised across the developing cell pla te. The localisation extended both to the zone of overlap of the two interd igitating sets of phragmoplast microtubules at the edge of the expanding ce ll plate and to the remainder of the plate devoid of phragmoplast microtubu les. Induction of cytokinetic arrest in onion and Arabidopsis thaliana by c affeine or brefeldin A produced disrupted phragmoplasts and centrin-labelle d cell plates, indicating that the localisation of centrin is coupled to th e deposition of the cell plate by the phragmoplast.