Manipulation by Tridemorph, a Systemic Fungicide, of the Sterol Composition of Maize Leaves and Roots

Abstract

The roots of maize (Zea mays L. var LG11) seedlings were watered with a solution of Tridemorph (2,6-dimethyl-N-tridecyl-morpholine), a systemic fungicide, for 3 to 4 weeks from the onset of germination. Very few △⁵-sterols, the major sterols of the control, were detected in the treated plants, and 9β,19-cyclopropyl sterols accumulated dramatically in both roots and leaves. △⁸-sterols were also found when low concentrations of the drug were used. The time course of the accumulation of the new sterols has been studied in plants treated with various concentrations (1-20 milligrams per liter) of Tridemorph. We found that: (a) cycloeucalenol-obtusifoliol isomerase, an enzyme opening the cyclopropane ring of cyclopropyl sterols, was strongly inhibited by the drug; and (b) the drug diffused readily from the roots to the whole plant and reached its enzymic targets in most of the leaf cells. The data obtained offer an opportunity to evaluate the physiological and biochemical consequence of the almost complete replacement of △⁵-sterols by cyclopropyl sterols in higher plant cells.