RAPID REORGANIZATION OF MICROTUBULAR CYTOSKELETON ACCOMPANIES EARLY CHANGES IN NUCLEAR PLOIDY AND CHROMATIN STRUCTURE IN POSTMITOTIC CELLS OF BARLEY LEAVES INFECTED WITH POWDERY MILDEW

Post-mitotic epidermal cells of barley leaves were found to contain, i n addition to cortical microtubules (CMTs), distinct arrays of endopla smic microtubules (EMTs). These encircle nuclei and continuously merge into the CMT arrays that underly the plasmalemma. Detailed three-dime nsional reconstruction of both types of MTs during fungal infection sh owed that profound and very rapid MT rearrangements occurred especiall y in the case of incompatible (resistant) barley-powdery mildew genoty pe combination. The most early MT responses, followed by their subsequ ent complete disintegration, were recorded around nuclei. These events might be relevant for the induction of such nuclear processes as onse t of DNA synthesis and nuclear chromatin condensation. Observed patter n of early infection events, as well as less prominent responses in th e case of compatible (susceptible) barley-powdery mildew genotype comb ination, both findings suggest that rapid reorganization of the MT cyt oskeleton could be involved in recognition of the fungus by host cells and in the initiation of resistance responses in barley leaves. We hy pothesize that the integrity and dynamics of the MT cytoskeleton, espe cially of its perinuclear part, might participate in control mechanism s involved in activation of resistance genes.