REGULATION IN BIOSYNTHESIS OF CHLOROPHYLL IN CHLOROPLAST OF CULTURED CELLS OF LIVERWORT

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Chloroplastidic terpenoids were believed for long time to be biosynthesized via mevalonate utilizing pathway. They have, however, very recently been proven to be biosynthesized via non-mevalonate mediating pathway. The objectives of this research are to demonstrate a mechanism of preferential labelling in the formation of isoprenoids within chloroplasts of livewort and to prove a simultaneous operation of mevalonate utilizing pathway and non-mevalonate-mediating pathway. I also verified involvement of acetate assimilation in biosynthesis of chloroplastidic terpenoids.The ^2H- and ^<13>C-labelled acetate, glycerol and glucose were fed to the suspension cultures of H.planus to verify involvement of non-mevalonate pathway and acetate assimilation in the formation of chloroplastidic terpenoids. To elucidate the mechanism of the preferential labelling of the FPP-derived portion, we isolated chloroplasts from protoplasts which are prepared from cultured cells oh H.planus. and incubated with … More non-labelled, and ^3H and ^<14>C labelled mevalonate, isoprenyl diphosphate (IPP) and FPP.Labelling patterns of the phytyl side chain incorporating [6,6-^2H_2]-glucose and [2-^<13>C]-glycerol indicated that non-mevalonate pathway involves the biosynthesis of the phytyl side chain. Labelling patterns of the phytyl side chain incorporating labelled acetate demonstrate two important results, i.e. (1) intact acetate was decomposed prior to the formation of mevalonate. Acetate was reformed either from two methyl carbons or two carboxy carbon. Mevalonate was formed from the reformed acetate, and (2) these findings suggest that mevalonate was also formed in chloroplasts. And acetate was assimilated by a consecutive passages of TCA cycle, reductive pentose phosphate cycle and glycolic path way.Radioisotopically labelled FPP was effectively incorporated into chloroplasts and converted to geranylgeranyl moiety and phytyl moiety very rapidly, while labelled mevalonate was incorporated to these compounds to a less extent. These results indicated that chloroplasts can take in FPP directly (or indirectly) and then convert it to geranylgeranyl diphosphate (GGPP). While mevalonate might be incorporated into chloroplasts at very low level but it can be metabolized to GGPP within chloroplasts. They also indeed indicate that the preferential labelling of the FPP-derived portion was caused by direct (or indirect) uptake of FPP by chloroplasts. Less