GAMMA-TUBULIN IS ASSOCIATED WITH A CORTICAL-MICROTUBULE-ORGANIZING ZONE IN THE DEVELOPING GUARD-CELLS OF ALLIUM-CEPA L

A key event in the differentiation of elliptically shaped guard cells such as those in Allium is the formation of a radial array of cortical microtubules (Mts) which, by controlling the orientation of wall micr ofibrils, plays an important role in cell shaping. Previous experiment s strongly indicated that the array is nucleated in a zone adjacent to the new ventral wall soon after cytokinesis. In order to further clar ify the function of this zone, we performed dual immunolocalizations o n Allium guard cells with anti-beta-tubulin, to detect Mts, and an ant ibody to gamma-tubulin, a protein known to be present at Mt-organizing centers in other species and recently identified in plants as well. G amma-Tubulin antibody stained the cortical zone adjacent to the ventra l wall, while little or no fluorescence was present elsewhere along th e radial Mt array or at other sites in the cell. The antibody also sta ined the mitotic poles and phragmoplast in guard mother cells, as it d oes in other material. No staining was seen when the primary antibody was omitted. The results are consistent with nucleation of the radial array at a cortical-Mt-organizing zone next to the ventral wall, and s et the stage for more in-depth studies on the spatial and temporal con trol of Mt formation in differentiating cells.