Effect of tobacco mosaic virus infection on glucose metabolism in Nicotiana tabacum var. Samsun. III. Investigation of hexosemonophosphate shunt enzymes and steroid concentration and biosynthesis.

Activity of the enzymes phosphoriboisomerase, glucose-6-phosphate and 6-phosphogluconic acid dehydrogenases were assayed in healthy and TMV-infected roots of Nicotiana tabacum L. var. Samsun plants grown in nutrient culture. The results indicate that all enzymes were equally active in both infected and healthy tissues. Endogenous sterol concentration in TMV-infected and healthy N. tabacum leaves, stems, and roots were investigated. Sterol biosynthesis was studied by infusing mevalonic acid-2-14C (MVA-14C) into TMV-infected and healthy tissues and isolating the sterol fraction by silicic acid column chromatography. The component sterols of the total sterol fraction were identified by gas-liquid chromatography. Infection with TMV had no effect on the level of sterols in roots, stems or leaves. Healthy and TMV-infected plants were not significantly different in their ability to synthesize sterols from MVA-14C. Cholesterol, campesterol, stigmasterol, and beta-sitosterol were identified as the major constituents of the total sterol fraction from stem and leaf tissues.