PLANT PHYSIOLOGY , Vol 105, Issue 2 529-534, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Light-Stimulated Carotenoid Biosynthesis during Transformation of Maize Etioplasts Is Regulated by Increased Activity of Isopentenyl Pyrophosphate Isomerase
M. Albrecht and G. Sandmann
Lehrstuhl fur Physiologie und Biochemie der Pflanzen, Universitat Konstanz, P.O. Box 5560, D-78434 Konstanz, Germany
Light-stimulated carotenoid biosynthesis associated with the transformation
of etioplasts to chloroplasts was investigated after dark-grown maize (Zea
mays) seedlings were transferred into light. These studies focused on the
enzymes of the pathway to detect those enzyme activities that were
stimulated in the light and thus that were responsible for increased
biosynthesis of carotenoids. In preliminary experiments, norflurazon, an
inhibitor of phytoene desaturase, was used to prevent phytoene being
further metabolized to carotenoids. Light-dependent stimulation of phytoene
accumulation indicated that the light-regulated steps are located in the
pathway leading to phytoene synthesis. The use of the 14C- labeled
precursors mevalonic acid, isopentenyl pyrophosphate, and farnesyl
pyrophosphate pointed to increased activity of an enzyme involved in the
biosynthetic steps between isopentenyl pyrophosphate and farnesyl
pyrophosphate. Determination of the activities of all five enzymes of the
pathway involved in the sequence from mevalonic acid to phytoene revealed
that the only enzyme activity stimulated by light was isopentenyl
pyrophosphate isomerase. Over a 3-h period of illumination, this enzyme
activity, like carotenoid biosynthesis, was stimulated 2.8-fold.
