DYNAMIC REORGANIZATION OF MICROFILAMENTS AND MICROTUBULES IS NECESSARY FOR THE EXPRESSION OF NONHOST RESISTANCE IN BARLEY COLEOPTILE CELLS

To show the involvement of microfilaments and microtubules in non-host resistance of barley, partially dissected coleoptiles which had been inoculated with a non-pathogen, Erysiphe pisi, were treated with sever al actin and tubulin inhibitors. If the coleoptiles were not treated w ith any of the inhibitors, the non-pathogen always failed to penetrate the coleoptile cells. However, when coleoptiles were treated with act in or tubulin polymerization or depolymerization inhibitors, the non-p athogen was able to penetrate successfully and to form haustoria in co leoptile cells of a non-host plant, barley. Actin polymerization inhib itors, cytochalasins, were more effective in causing an increase in pe netration efficiency of E. pisi than tubulin inhibitors. The effects o f cytochalasins depended on the kind of cytochalasin; the strength of the actin depolymerizing activity correlated significantly with the ef ficiency of increasing the penetration of the non-pathogen. When both actin and tubulin inhibitors were added simultaneously, the polarizati on of defense-related responses, such as massive cytoplasmic aggregati on, deposition of papillae and accumulation of autofluorescent compoun ds, at fungal penetration sites was suppressed. Actin inhibitors did n ot affect arrangement and stability of microtubules and vice versa, an d a double treatment of coleoptile cells with both microfilament and m icrotubule inhibitors showed an additive effect in increasing the pene tration efficiency of E. pisi. Furthermore, cytochalasin A treatment a llowed other non-pathogens, Colletotrichum lagenarium and Alternaria a lternata, to penetrate successfully into the non-host barley cells. Th ese results strongly suggest that microfilaments and microtubules migh t play important roles in the expression of non-host resistance of bar ley.