| Abstract: | The effects of IBP (S-benzyl O,O-diisopropyl phosphorothioate) on tips of single hyphae of Pyricularia oryzae were investigated by interference contrast microscopy. Labelling hyphae with calcofluor white followed by IBP treatment revealed that elongation of apices of almost all hyphae at the colony margin was inhibited after treatment for 4 h. Successive observations on single hyphae of an IBP-sensitive isolate indicated that apical cells stopped elongating approximately 10 min after the onset of treatment with 2 μg IBP ml?l. Small vacuoles appeared after 50 min; later they increased in number and size, and coalesced, finally producing a chain-like arrangement of vacuoles in the cytoplasm. When hyphae were treated with 10 μg IBP ml?1, cessation of elongation and vacuolation occurred earlier than when treated with 2 μg ml?1. Apical cells of hyphae of an IBP-tolerant isolate appeared unaltered even when treated with 10 μg ml?1. These results indicate that a major effect of IBP is to inhibit specifically the growth of apical cells of the IBP-sensitive isolate. |
