Low levels of gibberellic acid control the biosynthesis of ajmalicine in Catharanthus roseus cell suspension cultures.

In periwinkle cell suspensions, amounts of gibberellic acid ranging from 10 ( - 10) M to 10 ( - 7) M significantly antagonized, in a dose-dependant manner, the stimulation of ajmalicine biosynthesis by cytokinins (CKs). This inhibitory effect was strictly correlated with the abolition of the expression of two genes encoding enzymes of the monoterpenoid indole alkaloid (MIA) biosynthetic pathway and was normally upregulated after CK treatments. Moreover, low concentrations of the gibberellin biosynthesis inhibitor paclobutrazol could reverse the inhibitory effects of low auxin levels on ajmalicine accumulation in the cells. On the other hand, gibberellic acid could not affect the expression of two type-A response regulators considered to be CK primary response genes in periwinkle cells. The antagonistic effects of gibberellins and cytokinins on MIA biosynthesis and their possible impact on elements of the signal transduction are discussed.

Synthesis and biological evaluation with plant cells of new fosmidomycin analogues containing a benzoxazolone or oxazolopyridinone ring.

Fosmidomycin, 3-(N-formyl-N-hydroxyamido) propylphosphonic acid sodium salt, is an efficient inhibitor of 1-deoxy-D-xylulose-5-phosphate (DOXP) reductoisomerase, the second enzyme of the 2C-methyl-D-erythritol-4-phosphate (MEP) pathway notably present in Plasmodium species. We have synthesized a new series of analogues of fosmidomycin, containing a benzoxazolone, benzoxazolethione or oxazolopyridinone ring. As the MEP pathway is involved in the biosynthesis of all isoprenoids, accumulation of ajmalicine in Catharanthus roseus cells was chosen as a marker of monoterpenoid indole alkaloid (MIA) production. None of the twelve studied phosphonic esters 3 and phosphonic acids 4 affected periwinkle cell growth, but some of them (3c, 3e, 3g and 3h) showed a significant inhibition of ajmalicine accumulation: 45-85% at 125 microM. Surprisingly, this effect disappeared by conversion of 3c and 3g into the corresponding acids 4c and 4g, respectively.

Effect of the hydroalcoholic extract of rauwolfia ligustrina on smooth and cardiac muscles in-vitro.

The actions of the hydroalcoholic extract (HE) of Rauwolfia ligustrina (the whole plant) on agonist-induced contractions were analysed in the rat uterus and guinea-pig ileum and trachea, and also in rat atrium contracting spontaneously in-vitro. The HE (100-400 micrograms mL-1) caused concentration-dependent rightward shifts of the concentration-response curves and reduced the maximal contraction induced by oxytocin, bradykinin, angiotensin II, prostaglandin F2 alpha and acetylcholine in the rat uterus. The calculated mean IC50 values were: 300, 147, 158, 197 and 105 micrograms mL-1, respectively. In the guinea-pig ileum the HE also caused graded displacement to the right of the concentration-response curves for bradykinin, histamine and carbachol, associated with pronounced inhibition of the agonist-induced maximal contractions. The calculated mean IC50 values were 165, 134 and 241 micrograms mL-1, respectively. The HE (100-3000 micrograms mL-1) caused graded relaxation (IC50 of 271 micrograms mL-1) of strips of guinea-pig trachea precontracted with carbachol (0.2 microM). This effect was not influenced by propranolol (1 microM), 3-isobutyl-1-methylxanthine (1 microM) or methylene blue (10 microM), but was significantly potentiated (1.5-to 3-fold) by indomethacin (3 microM) and forskolin (1 nM). In addition, NG-monomethyl-L-arginine (L-NMMA, 100 nM) significantly reduced the HE-induced maximal relaxation, while indomethacin (3 microM) potentiated the HE response. Finally, the HE caused a concentration-dependent and long-lasting inotropic effect in the rat right atrium, contracting spontaneously with a mean EC50 value of 409 micrograms mL-1. It is suggested that the effects of the HE of R. ligustrina on smooth and cardiac muscles "in-vitro' may result from its ability to interact, at least partially, with the cAMP pathway.