Isoprenoid biosynthesis in callus cultures of Croton sublyratus

Abstract

The leaves and callus cultures of Croton sublyratus Kurz were used to determine glucose uptake in experiments to study the original source of isopentenyl diphosphate (IPP) biosynthesis, the universal isoprene unit was possibly formed from either the classical mevalonate pathway or the novel non-mevalonate pathway. The leaves appeared to accumulate plaunotol as oil globules within the chloroplasts of palisade mesophyll cells as observed under electron microscope operation of subcellular organelles of plaunotol-containing tissues, which was confirmed by plaunotol detection in specific leaf tissues. [1-14C]glucose uptake into a leaf showed low incorporation into plaunotol. The callus cultures, on the other hand, did not seem to produce plaunotol but it was found highly active in producing a mixture of two phytosterols, namely stigmasterol and beta-sitosterol. [1-13C]glucose uptake into the callus cultures showed a very high incorporation of the labeled glucose into both forms of phytosterol. Isolation of the labeled products followed by 13C NMR analysis showed that phytosterols had their 13C labeling pattems corresponding to the biosynthetic pathways of both the mevalonate pathway and non-mevalonate pathway. Since the biosynthesis of phytosterols has so far been reported to be mainly from the mevalonate pathway, therefore, this study provides original information on the biosynthesis of phytosterols via the novel non-mevalonate pathway.