Abstract: The effects of flumorph on the synthesis and distribution of cell wall materials of Phytophthora melonis were investigated by the biochemical methods of isotopic trace and histological fluorescent staining. The synthesis of cellulose and noncellulose glucan was significantly inhibited by flumorph from 1 h to 4 h after the germling suspensions of P. melonis exposure to flumorph and the inhibition was dose-dependent. The rate of inhibition reached 22.78% and 34.67% after exposure to 25 μg/mL flumorph for 1 h and 4 h later, respectively. Subsequently the synthesis of cellulose increased from 4 h to 8 h, and then was inhibited again after 16 h treatment. The change of inhibition of flumorph on cell wall synthesis was consistent with the alteration of hyphal morphology. Flumorph can significantly inhibit the diameter of colony, but it also can cause stunting of hyphae and stimulate the formation of short lateral branches after exposure to flumorph for 4 h to 8 h. The other most characteristic effect of flumorph treatment was that the development of the periodic expansion along hyphae yielded a "beaded" morphology. These data above show that flumorph did not inhibit the synthesis of cellulose and other cell wall materials, the hyphae can grow continually, but its morphology was abnormal. After being stained with calcofluor, it was observed that the synthesis of new cell wall was going on, but they uniformly deposited throughout the diffuse expanded cell walls, in contrast to their normal polarized patterns of deposition. These may be the result of that the disruption of cell polarity, because the change of hyphae morphology and patterns of deposition of newly synthesized cell wall after exposure to flumorph were similar to the characteristics of disrupted process of the polarity growth of cell in other eukaryotic cells. Thus, the results obtained in this study suggest that flumorph might cause the disruption of establishment of cell polarity. Subsequently, the newly synthesized cellulose lost their normal polarized patterns of deposition, but the synthesis of cell wall materials was not interfered.

Key words: Flumorph, Cell wall synthesis, Cell polarity, Isotope trace, Calcofluor