, Volume 191, Issue 1-2, pp 79-83

Changes in intracellular pH during zoosporogenesis inPhytophthora cinnamomi

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Changes in intracellular pH (pHi) have been examined during zoosporogenesis inPhytophthora cinnamomi in order to elucidate the molecular mechanisms that bring about initiation of the orderly cleavage of the sporangium. By microinjecting a dextranconjugated pH-sensitive fluorescent indicator, 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF dextran), and using fluorescence ratio image analysis, the pHi of a sporangium was monitored throughout the process of zoosporogenesis. The pHi of mature sporangia was found to remain constant at pH 6.84 ± 0.05 (mean ± SE, n=6) at room temperature (24 °C), but increased to 7.04 ± 0.04 (p < 0.001) during a 20 min cold treatment at 19 °C. As the process of zoosporogenesis proceeded, the increased level of pHi was maintained for 30–40 min after initiation of the cold shock. Zoosporogenesis was blocked when the pHi of the sporangium was held constant by microinjecting with 10 mM HEPES buffer (pH 7.0) before cytoplasmic cleavage was induced by a cold shock. In contrast, no inhibitory effect was observed when sporangia were microinjected with HEPES buffer after the cold shock. These results indicate that initiation of cytoplasmic cleavage requires a rise in pHi.