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Sclareol, an antifungal specialized metabolite produced by clary sage, Salvia sclarea, is the starting plant natural molecule used for the hemisynthesis of the perfume ingredient ambroxide. Sclareol is mainly produced in clary sage flower calyces; however, the cellular localization of the sclareol biosynthesis remains unknown. To elucidate the site of sclareol biosynthesis, we analyzed its spatial distribution in the clary sage calyx epidermis using laser desorption/ionization mass spectrometry imaging (LDI–FTICR-MSI) and investigated the expression profile of sclareol biosynthesis genes in isolated glandular trichomes (GTs). We showed that sclareol specifically accumulates in GTs' gland cells in which sclareol biosynthesis genes are strongly expressed. We next isolated a glabrous beardless mutant and demonstrate that more than 90% of the sclareol is produced by the large capitate GTs. Feeding experiments, using 1-13C-glucose, and specific enzyme inhibitors further revealed that the methylerythritol-phosphate (MEP) biosynthetic pathway is the main source of isopentenyl diphosphate (IPP) precursor used for the biosynthesis of sclareol. Our findings demonstrate that sclareol is an MEP-derived diterpene produced by large capitate GTs in clary sage emphasing the role of GTs as biofactories dedicated to the production of specialized metabolites. [ABSTRACT FROM AUTHOR]

The cornerstone of carbon ( C) and nitrogen ( N) metabolic interactions - respiration - is presently not well understood in plant cells: the source of the key intermediate 2-oxoglutarate (2 OG), to which reduced N is combined to yield glutamate and glutamine, remains somewhat unclear ., We took advantage of combined mutations of NAD- and NADP-dependent isocitrate dehydrogenase activity and investigated the associated metabolic effects in Arabidopsis leaves (the major site of N assimilation in this genus), using metabolomics and 13 C-labelling techniques., We show that a substantial reduction in leaf isocitrate dehydrogenase activity did not lead to changes in the respiration efflux rate but respiratory metabolism was reorchestrated: 2 OG production was supplemented by a metabolic bypass involving both lysine synthesis and degradation., Although the recycling of lysine has long been considered important in sustaining respiration, we show here that lysine neosynthesis itself participates in an alternative respiratory pathway. Lys metabolism thus contributes to explaining the metabolic flexibility of plant leaves and the effect (or the lack thereof) of respiratory mutations. [ABSTRACT FROM AUTHOR]

Many horticultural and natural plant species have variegated leaves, that is, patchy leaves with green and non-green or white areas. Specific studies on the metabolism of variegated leaves are scarce and although white (non-green) areas have been assumed to play the role of a 'nitrogen store', there is no specific studies showing the analysis of nitrogenous metabolites and the dynamics of nitrogen assimilation. Here, we examined the metabolism of variegated leaves of Pelargonium x hortorum. We show that white areas have a larger N : C ratio, more amino acids, with a clear accumulation of arginine. Metabolomic analyses revealed clear differences in the chemical composition, suggesting contrasted metabolic commitments such as an enhancement of alkaloid biosynthesis in white areas. Using isotopic labelling followed by nuclear magnetic resonance or liquid chromatography/mass spectrometry, we further showed that in addition to glutamine, tyrosine and tryptophan, N metabolism forms ornithine in green area and huge amounts of arginine in white areas. Fine isotopic measurements with isotope ratio mass spectrometry indicated that white and green areas exchange nitrogenous molecules but nitrogen export from green areas is quantitatively much more important. The biological significance of the metabolic exchange between leaf areas is briefly discussed. Metabolic differences between green and white parts of variegated leaves, which may help understanding nitrogen assimilation and partitioning in horticultural species, are poorly documented. Here, using integrative and isotopic methods, an enhancement of amino acid and alkaloid synthesis in white parts and an exchange of nitrogenous compounds between leaf parts is demonstrated. White parts seem to play the role of an advantageous 'nitrogen reserve' to sustain leaf metabolism. [ABSTRACT FROM AUTHOR]