Redistribution of annexin in gravistimulated pea plumules

We used immunocytochemistry to investigate the effects of gravistimulation on annexin localization in etiolated pea plumule shoots. In longitudinal se ctions, an asymmetric annexin immunostaining pattern was observed in a defi ned group of cells located just basipetal to apical meristems at the main s hoot apex and at all of the axillary buds. an area classically referred to as the leaf gap. The pattern was observed using both protein-A-purified ant i-annexin and affinity-purified anti-annexin antibodies for the immunostain ing. A subset of the cells with the annexin staining also showed an unusual ly high level of periodic acid Schiff (PAS) staining in their cell walls. P rior to gravistimulation, the highest concentration of annexin was oriented toward the direction of gravity along the apical end of these immunostaine d cells. In contrast. both at 15 and 30 min after gravistimulation, the ann exin immunostain became mon evenly distributed all around the cell and more distinctly cell peripheral. The asymmetry along the lower wall of these ce lls was no longer evident. In accord with current models of annexin action, we interpret the results to indicate that annexin-mediated secretion in th e leaf gap area is preferentially toward the apical meristem prior to gravi stimulation. and that gravistimulation results in a redirection of this sec retion. These data are to our knowledge the first to show a correlation bet ween the vector of gravity and the distribution of annexins in the cells of flowering plants. (C) 2000 Editions scientifiques et medicales Elsevier SA S.