Soybean isoflavones trigger a calcium influx in Phytophthora sojae

Both the motile zoospores and the hyphal germ tubes of Phytophthora sojae r espond chemotropically to the soybean isoflavones daidzein and genistein. T he role of Ca2+ in the cellular response to these host signals was investig ated by using X-ray microanalysis of cells to monitor net changes in cellul ar levels of Ca2+ and by quantifying the effects of exogenous Ca2+ and daid zein on the developmental fate of encysted zoospores. Confirmation that iso flavones trigger a net influx of Ca2+ into the cell was demonstrated by X-r ay microanalysis of individual encysted zoospores. Zoospores exposed to 10 mM Ca2+ and 1 mu M daidzein at the time of encystment formed cysts that con tained more Ca2+ than zoospores exposed to Ca2+ alone. The magnitude of int ernal Ca2+ stores appears to be a determining factor affecting the developm ental fate of P. sojae cysts. (C) 1999 academic Press.