Metabolic engineering of isoprenoid biosynthesis in Arabidopsis for the production of taxadiene, the first committed precursor of Taxol

Paclitaxel (Taxol) is a widely used anticancer isoprenoid produced by the secondary metabolism of yew (Taxus sp.) trees. However, only limited amounts of Taxol or related metabolites (taxoids) can be obtained from the currently available sources. In this work we have taken the first step toward genetically engineering the biosynthesis of taxoids in angiosperms. The first committed step in Taxol biosynthesis is the production of taxadiene from geranylgeranyl diphosphate (GGPP), catalyzed by the plastid-localized enzyme taxadiene synthase (TXS). A recombinant T. baccata TXS lacking the putative plastid targeting peptide and fused to a C-terminal histidine (His) tag was shown to be enzymatically active in Escherichia coli. Constitutive production of the full-length His-tagged enzyme in Arabidopsis thaliana plants led to the accumulation of taxadiene and concomitant growth retardation and decreased levels of photosynthetic pigment in transgenic plants. Although these phenotypes may derive from a toxic effect of taxadiene, the lower accumulation of endogenous plastid isoprenoid products such as carotenoids and chlorophylls in transgenic plants also suggests that the constitutive production of an active TXS enzyme might alter the balance of the GGPP pool. Induction of transgene expression using a glucocorticoid-mediated system consistently resulted in a more efficient recruitment of GGPP for the production of taxadiene, which reached levels 30-fold higher than those in plants constitutively expressing the transgene. This accomplishment illustrates the possibility of engineering the production of taxoids and other GGPP-derived isoprenoids in crop plants despite the constraints associated with limited knowledge with regard to regulation of GGPP availability.     

A propos de coefficients de temperature en biologie

Sommaire Une revue des bases théoriques de l'équation proposée parBlehrádek montre que celle-ci n'est autre chose que l'équation d'Esson écrite d'une autre manière (substitution de t° centigrade à T, température absolue). La raison de cette substitution de graduation est basée sur la prétendue existence d'un «zéro biologique» au voisinage de 0° centigrade; impliquant par là, l'équivalence pour un système organique du 0° centigrade au 0° absolu pour un système inorganique.La déduction d'un «coefficient» de température pour la viscosité cellulaire est, de plus, absolument non fondée. Elle repose sur des expériences inadéquates ou sur des extensions illégitimes de raisonnement.Sa revue de l'applicabilité de l'équation d'Arrhenius se montre de plus incorrecte dans son traitement. Elle se base sur des travaux dont les données d'observation sont fréquemment plus que critiquables. Elle montre de plus le grand danger des «moyennes d'observations» ainsi que la nécessité, pour tout travail sur la relation entre l'activité d'un organisme vivant et la température, de procéder à un grand nombre de points de l'échelle thermométrique. Cette technique permet alors de mettre en évidence l'existence de températures critiques pour le processus considéré.     

Dynorphin-Related Opioid Peptides in the Neurointermediate Pituitary of Rats Are Not α-N-Acetylated

Immunoreactive dynorphin in the neurointermediate pituitary of rats was found to consist of four different molecular weight forms. The three larger molecular weight forms, with apparent molecular weights of 4800, 3200, and 1700, constituted more than 80% of the total dynorphin immunoreactivity, and each liberated leucine-enkephalin but not alpha-N-acetyl-leucine-enkephalin upon enzymatic treatment with trypsin followed by carboxypeptidase B. Only a minor portion of the smallest dynorphin-related molecular weight form, dynorphin-(1-8), released alpha-N-acetyl-leucine-enkephalin upon enzymatic cleavage. This suggests that the vast majority of dynorphin-related peptides in the rat neurointermediate pituitary is not alpha-N-acetylated. The exceptionally high opiate-like activity of the molecular weight 1700 dynorphin suggests that this dynorphin-related opioid peptide may constitute the major part of opioid activity in the neurointermediate pituitary of rats.     

Fortress Holland? Support for ethnocentric policies among the 1994‐electorate of The Netherlands

Abstract

The Dutch have a long tradition of hospitality towards ethnic immigrants. In the nineties, however, quite dramatic changes have taken place among the Dutch. The central question addressed in this contribution is: to what extent do specific categories within the electorate favour ethnocentric policies? This question is answered by deducing hypotheses that are tested using recent data polled within the framework of the Dutch National Election Studies. Our crucial conclusion is that a rather widespread support for ethnocentric policies is present in contemporary Dutch society, especially among manual labourers, self‐employed and lowly educated people, but also among young cohorts and among modal income categories.     

Involvement of endorphins in emotional hyperthermia of rats

When rats were confronted with the novel experience of a new environment and stressful handling procedure their body temperature increased within minutes. At the same time β-endorphin-like immunoreactivity in the plasma increased dramatically. The stress-induced hyperthermia could be antagonized or reversed by the active, not however, by the inactive enantiomer of naloxone. The data provide evidence for a physiological role of endorphins.     

Composition and Intraspecific Chemical Variability of Leaf Essential Oil of Laggera pterodonta from Côte d'Ivoire

The chemical composition of 44 leaf oil samples of Laggera pterodonta (DC.) Sch.Bip. ex Oliv. (Asteraceae) from Côte d'Ivoire was investigated, using combination of chromatographic (GC‐FID) and spectroscopic (GC/MS, ¹³C‐NMR) techniques. Two oil samples chosen according to their chromatographic profiles were submitted to column chromatography and all fractions of CC were analyzed by GC‐FID, GC/MS and ¹³C‐NMR. In total, 83 components accounting for 96.5 to 99.4 % of the whole chemical composition were identified. Significant variations were observed within terpene classes: monoterpene hydrocarbons (0.4–22.7 %), oxygenated monoterpenes (32.9–54.9 %), sesquiterpene hydrocarbons (18.6–38.3 %) and oxygenated sesquiterpenes (3.5–38.4 %). Thus, the 44 compositions were subjected to hierarchical cluster analysis (HCA) and principal component analysis (PCA). Two groups were differentiated according to their composition. All the samples contained 2,5‐dimethoxy‐p‐cymene, α‐humulene and (E)‐β‐caryophyllene among the main components. Other components were present at appreciable contents and allowed differentiation of two groups: sabinene and germacrene D for Group I; 10‐epi‐γ‐eudesmol and eudesm‐7(11)‐en‐4α‐ol for Group II. All the samples collected in Eastern Côte d'Ivoire constituted Group I, while samples collected in the Central area of the country constituted Group II.