Influence of a Ceratocystis ulmi Toxin on Water Relations of Elm (Ulmus americana).

Water-soluble glycopeptides isolated from cultures of Ceratocystis ulmi have been reported to be toxins involved in Dutch elm disease. The influence of the glycopeptides on the water relations of Ulmus americana seedlings was tested by placing cut stems in glycopeptide preparations. After 4 hours in 200 micrograms per milliliter toxin the stem conductance of the seedlings was reduced by 79% and the leaf water potential was reduced by 3 bars to that at which the seedlings wilted, the stomata closed, and transpiration decreased. Decrease in stem conductance as the mode of action of the toxin was further confirmed by forcing toxin through the stem and petiole of elm and measuring the effects on stem conductance. High molecular weight dextrans were found to mimic the action of toxin on stem and petiole conductance, and their ability to do so was found to be correlated with their molecular weight. As low as 4 micrograms of toxin or dextrans were found to measurably decrease the stem and petiole conductance of elms. Disruption of the water-conducting system of elms and other plants by small quantities of high molecular weight compounds may be a factor in diseases with wilting symptoms.