SUMMARY: A number of organic compounds were tested to determine their ability to induce encystment or germination of zoospores of the fungus, . The basic amino acids, lysine and arginine, induced encystment at concentrations in the millimolar range. Pectin (500 λg ml) also induced encystment and in addition stimulated the encysted cells to germinate. A wide range of carbohydrates and the amino acids, glutamate and aspartate, stimulated cysts to germinate although they did not themselves induce encystment.

The polypeptide, poly--lysine and the basic proteins, histone 1, histone 4 and lysozyme together with the lectin, concanavalin A, immobilized swimming zoospores at concentrations between 0.3 and 10 λg ml. At concentrations below 1 λg ml cysts were formed but at higher concentrations cells lysed and the viability of the population was reduced. These compounds did not induce germination of the encysted zoospores. Ethanol, isovaleraldehyde and hexanal also induced encystment but only at concentrations in the millimolar range.

These data, together with previous work on cations show that the triggering of motile cells to encyst does not in this species invariably result in the cells being committed to germination.


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