Prenyllipid biosynthesis

Keller, Y, Bouvier, R, Dharlingue, A. and Camara, B. (1998b) Metabolic compart-mentation of plastid prenyllipid biosynthesis evidence for the involvement of a multifunctional geranylgeranyl reductase. Eur.. Biochem., 251,413-7. 

Prenyllipid biosynthesis under the influence of sethoxydim Most of the C-label was found in the sterol fraction, whereby the highest mol-specific radioactivity was detected in the 4-dimethyl and 4-methyl sterols, which are known as biosynthetic precursors of the desmethyl sterols (Table 6). High label was also found in the mitochondrial ubiquinone, which in maize leaves consists of the two homologues Q-9 and Q-10 (29). Much less radioactivity is found in the chloroplast prenyllipids (chlorophylls, carotenoids, prenyl-quinones) as is expected and known, since exogeneously applied mevalonic... 

Chromoplasts are ideal organelles for the study of carotene biosynthesis. The question arises what about chloroplasts in which in vivo apparently a carotenoid biosynthesis takes place. When chloroplasts or chloroplast subfractions are incubated in the presence of C-14 IPP a wide palette of prenyllipids is formed with the exception of carotenes (Table 2). Onyl in highly purified envelope fractions with very low contaminating chlorophyll synthase activities some phytoene synthase, phytoene dehydrogenase and cis-phytofluene isomerase activities have been described, when geranyIgerany1 pyrophosphate, not IPP, was provided as the substrate (ref. 23). 

In sethoxydim treated plants there are no differences in principle in the labelling pattern of the prenyllipids as compared to the controls (Table 6), though the specific labelling is generally higher. This indicates that the biosynthesis of the different prenyllipid classes is not affected by sethoxydim. It blocks the accumulation of chlorophylls and carotenoids, however. 

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