Prenyllipids

Lichtenthaler, H.K. 1982. Synthesis of prenyllipids in vascular plants (including chlorophylls, carotenoids, prenylquinones). In CRC Handbook of Biosolar Resrouces, Vol. I, part I Basic Principles (A. Matsui and C.C. Black, eds.) pp. 405-421. CRC Press, Boca Raton, Fla. 

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. 

Table III. Effect of mevinolin on plastidic prenyllipids and prenylquinones ...

Table IV. Differential inhibition of sterol accumulation and of the light-induced prenyllipid accumulation at high mevinolin concentration in excised 9-day-old etiolated primary wheat leaves during 18 h of continuous white light. Prenyllipids in U8 per 40 leaf segments. Mean of 2 runs with SD < 10%. X = Xanthopylls c = S-carotene x-i-c = sum of carotenoids. Chlorophylls and carotenoids were separated by TLC (1) and determined photometrically.

Precursor Acyllipids Chlorophyll/Prenyllipids Others (% of total incorporation into lipids) ... 

Within plant ceils carotenoids are synthesized exclusively in three types of piastids (chloroplasts, chromopiasts, and etioplasts) from the general prenyllipid precursor isopentenyl pyrophosphate (IPP). In this brief review I shall tackle three points of view, the formation or cellular compartmentation of formation, respectively, of the precursor IPP, the carotenoge-nic enzymes in chromopiasts and the carotenogenic enzymes in other piastids. 

The formation of IPP proceeds according tg the relatively well established scheme shown in Fig. 1, ultimately from acetyl-CoA. There are three sites or compartments in the plant cell lAihere prenyllipids are synthesized (i) the endoplasmic reticulum (ER) for sterol formation (ii) the piastids for the synthesis of the side chains of chlorophylls, quinones and tocopherols, and of the carotenoids and fatty acid prenyl esters (iii) the mitochondria for the synthesis of the ubiquinone side chains. Therefore, the question arises whether there are also three cellular sites for IPP formation, whereby the cytopiasm/ER is uncontested. ... 

When etioplasts from the cotyledons of these seedlings are incubated in tbe presence of C-14 intermediates of the IPP pathway no prenyllipid synthesis can be observed, whereas IPP itself is well incorporated (Table 1). In the presence of cytoplasmic supernatant, however, which contains all the enzymes necessary for IPP formation the intermediates are also well incorporated. 

Table 1. Sinapis cotyledon etioplasts. Prenyllipid synthesis from C-14 precursors in the absence and presence of cytoplasmic supernatant (CS). Chi, chlorophylls car, carotenes. From Lutke-Brinkhaus and Kleinig, in press.

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). 

Table 2. Sinapis alba etioplasts, etiochloroplasts, and chloroplasts. Formation of carotenes and other prenyllipids from C-14 IPP. geranylgeraniol/nonaprenol. From Lutke-Brinkhaus...

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... 

Table 6. Specific radioactivity (Bq/pMol) of prenyllipids after application of 2-l C -mevalonic acid to green excised maize shoots from 10 day old plants with and without application of sethoxydim.

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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