Cyclopropyl Sterol and Phospholipid Composition of Membrane Fractions from Maize Roots Treated with Fenpropimorph

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Abstract
Maize (Zea mays l.) caryoposes were grown in the presence of fenpropimorph, a systemic fungicide, for 7 days in the dark. Membrane fractions enriched, respectively, in endoplasmic reticulum, plasma membrane, and mitochondria were isolated from control and treated maize roots and analyzed for their free sterol, phospholipid, and fatty acid composition. In treated plants, the intracellular distribution of free sterols was dramatically modified both qualitatively and quantitatively. The normally occuring .DELTA.5-sterols disappeared almost completely and were replaced by 9.beta.,19-cyclopropyl sterols, mainly cycloeucalenol and 24-methyl pollinastanol. These new compounds were found to accumulate in all the membrane fractions in such a way that the endoplasmic reticulum-rich fraction became the richest one in free sterols instead of the plasma membrane. In contrast, the fenpropimorph treatment of maize roots was shown not to affect either the relative proportions or the amounts of the individual phospholipids, but an increase in the unsaturation index of phospholipid-fatty chains of the endoplasmic reticulum-rich fraction was observed. The present data suggest that, in higher plant membranes, cyclopropyl sterols could play a structural role similar to that of the bulk of .DELTA.5-sterols.