Thiol composition of a xylem-tapping mistletoe and the xylem sap of its hosts

Considerable amounts of low M(r) thiols were found in leaves, flowers and stems of the European mistletoe Viscum album (L). Leaf thiol contents were the highest so far reported for green tissue. Thiol composition was similar in all mistletoe organs analysed. Glutathione was the predominant low M(r) thiol of V. album independent of xylem sap thiol composition of the host. From the present findings it may be concluded that either cysteine removed from the xylem sap of the host is rapidly incorporated into glutathione in the endophytic system, or glutathione is selectively removed from the xylem sap of the host. The significance of de novo reduction of sulphate taken from the xylem sap of the host for the mistletoe's thiol composition and content remains to be elucidated.