Rauvolfia alkaloids cell cultures

Isolation of the stereospecific strictosidine s)mthase (STS) and formation of strictosidine with the 3a-(S) configuration proved conclusively that this was the natural precursor of the terpenoid indole alkaloids. Strictosidine occurs naturally in Rhazya stricta and the synthase has been isolated from a number of other species Amsonia salicifolia, A. tabemaemontam, Catharanthus pusillus, C. roseus, Rauvolfia verticillata, R. vomitoria, R. serpentina, Rhazya orientalis and Voacanga africana. The enzyme has been purified to homogeneity from R. serpentina (Hampp and Zenk, 1988). A comparison of the activity of STS from C. roseus roots, the only portion of the plant to contain ajmalicine, with that present in plant cell cultures producing the same alkaloid demonstrated that the plant cell cultures are far more metabolically active (Ziegler and Facchini, 2008). 

Biosynthesis The biosynthesis of these alkaloids begins with the key reaction, the condensation of tryptamine with secologanin to give strictosidine catalyzed by the enzyme strictosidine synthase. The biosynthesis was elucidated mainly by the use of plant cell suspension cultures. Cell cultures of Catharanthus and Rauvolfia species have been the subject of intense phytochemical studies. 

Conclusively, these three plant systems of Rauvolfia including cell suspension cultures, hybrid ceU suspension cultures, and hairy root cultures became available for the first analysis of their alkaloid pattern, including isolation and identification of the single alkaloid metaboUtes in concentrations of about 100 tg to 1.6 per liter nutrition medium. ... 

Tissue and cell cultures of Rauvolfia serpentina synthesize a plethora of alkaloids, dominated by yohimbine (5), ajmaline (37), and ajmalidine, which differed from that of any plant part and from undifferentiated cultures (Ellis, 1988). 

Plant Cells. The metabolism of unlabelled alkaloids in plant cell cultures has been followed using heteronuclear multiple quantum coherence NMR. The addition of ajmaline to cell suspension cultures of somatic hybrids of Rauvolfia serpentina Benth. ex Kurz and Rhazya stricta Decaisne (R x R cells) resulted in its conversion to raumacline. When, vinorine, an intermediate of ajmaline metabolism, was added to suspensions on R x R cells, vellosimine was formed and then converted to 10-deoxysarpagine. However, vinorine was apparently metabolised by a second pathway to vomilenine or raucaffricine." ... 

Thirty-six plant species tested in cell suspension culture could be elicited by exogenously supplied methyl jasmonate to accumulate secondary metabolites by a factor of 9 to 30 over the control values. Induction by MJ was not specific to any one type of secondary metabolite but rather general to a wide spectrum of low molecular weight substances ranging from flavonoids, guaianolides and anthraquinones to various classes of alkaloids [96]. Endogenous jasmonic acid and its methyl ester (MJ) accumulate rapidly and transiently after treatment of plant cell suspension cultures of Rauvolfia canescens and Eschscholtzia califor-nica with a yeast elicitor [97]. 

Figure 3 Overview on the structural diversit)r of detected and identified indole alkaloids produced in cell suspension cultures of Rauvolfia.

Figure 4 Additional indole alkaloids produced in intergeneric hybrid cell suspension cultures of Rauvolfia serpentina x Rhazya stricta after treatment with methyljasmonate. ...

The enzyme which follows the vinorine synthase was commonly named vinorine hydroxylase. VH is responsible for the generation of vomiienine (29) by selective hydroxylation of vinorine (17) at the C-21 position (Figure 18). The reaction is catalyzed exclusively by a microsomal protein from Rauvolfia cultured cells in the presence of the substrate vinorine, NADPH, and O2. The investigation of the taxonomical distribution of the enzyme indicated that vinorine hydroxylase is exclusively present in ajmahne-producing plant cells. It was also observed that the substrate specificity of VH was high. Alkaloids with vinorine-related structures such as fJ-tetra-phyllicine or its Z-configurated isomer were not hydroxylated... 

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