Albitization in the Inkisi Sandstones, Republic of Congo: Characterization and Interpretation

Albitization appears to be one of the most important transformations affecting aluminium silicates in the superficial zone of the Earth’s crust, occurring in a variety of different formations. However, this process has not yet been clearly recognized in Africa. In this paper, we present the process of albitization in the context of an African sedimentary basin, in particular the Neoproterozoic to Palaeozoic arkosic sandstones of the Niari basin in the Republic of Congo. Differents faciès, mineral parageneses associated, chemical compositions of these albitizations are presented. The morphology of these albitization textures, which are often developed as a peripheral halo composed of pure albite surrounding (with a sharp contact) the practically unaltered potassium feldspar, would argue in favour of in situ albitization. In the same way, the presence of calcium-rich zones sometimes surrounding the albitized domains would support this hypothesis, the calcium being exsolved at the outer grain boundary during in situ formation of the albite. Thus, the presence of in situ albitization in the Inkisi sandstone could indicate an important marine influence on the sedimentary environment and diagenesis of these sandstones.Keywords: Albitization, Sandstone, Inkisi, Congo, Feldspa

Le marcottage aerien de Grewia coriacea Mast.

Grewia coriacea, tree from 4 to 25 m in height and 12 to 40 cm in diameter is a plant of the Congoleses forests. Its fruits use the manufacture of several drinks. The barks are used in pharmacopeia. The sectionof the branches and the demolition of the tree practised in the zones of production, like method of gathering of the fruits, the practice of the itinerant culture on brûlis, involve the crumbling of this botanical capital. Also, we undertook tests of layering in order to perennialize this species. All the marcottes emitted the roots before 3 months. The orthotropic branches and plagiotropes seem to be adapted best to the layering. Key words: Grewia coriacea Mast, layering, oblique, orthotropic, plagiotrope, branche

Abscisic acid negatively regulates elicitor-induced synthesis of capsidiol in wild tobacco (Nicotiana plumbaginifolia)

International audienc

Abscisic acid negatively regulates elicitor-induced synthesis of capsidiol in wild tobacco (Nicotiana plumbaginifolia)

International audienc

Characterization of plant carotenoid cyclases as members of the flavoprotein family functioning with no net redox change

International audienceThe later steps of carotenoid biosynthesis involve the formation of cyclic carotenoids. The reaction is catalyzed by lycopene beta-cyclase (LCY-B), which converts lycopene into beta-carotene, and by capsanthin-capsorubin synthase (CCS), which is mainly dedicated to the synthesis of kappa-cyclic carotenoids (capsanthin and capsorubin) but also has LCY-B activity. Although the peptide sequences of plant LCY-Bs and CCS contain a putative dinucleotide-binding motif, it is believed that these two carotenoid cyclases proceed via protic activation and stabilization of resulting carbocation intermediates. Using pepper (Capsicum annuum) CCS as a prototypic carotenoid cyclase, we show that the monomeric protein contains one noncovalently bound flavin adenine dinucleotide (FAD) that is essential for enzyme activity only in the presence of NADPH, which functions as the FAD reductant. The reaction proceeds without transfer of hydrogen from the dinucleotide cofactors to beta-carotene or capsanthin. Using site-directed mutagenesis, amino acids potentially involved in the protic activation were identified. Substitutions of alanine, lysine, and arginine for glutamate-295 in the conserved 293-FLEET-297 motif of pepper CCS or LCY-B abolish the formation of beta-carotene and kappa-cyclic carotenoids. We also found that mutations of the equivalent glutamate-196 located in the 194-LIEDT-198 domain of structurally divergent bacterial LCY-B abolish the formation of beta-carotene. The data herein reveal plant carotenoid cyclases to be novel enzymes that combine characteristics of non-metal-assisted terpene cyclases with those attributes typically found in flavoenzymes that catalyze reactions, with no net redox, such as type 2 isopentenyl diphosphate isomerase. Thus, FAD in its reduced form could be implicated in the stabilization of the carbocation intermediate

Light-Induced Acclimation of the Arabidopsis chlorina1 Mutant to Singlet Oxygen.

International audienceSinglet oxygen (O-1(2)) is a reactive oxygen species that can function as a stress signal in plant leaves leading to programmed cell death. In microalgae, O-1(2)-induced transcriptomic changes result in acclimation to O-1(2). Here, using a chlorophyll b-less Arabidopsis thaliana mutant (chlorina1 [ch1]), we show that this phenomenon can also occur in vascular plants. The ch1 mutant is highly photosensitive due to a selective increase in the release of O-1(2) by photosystem II. Under photooxidative stress conditions, the gene expression profile of ch1 mutant leaves very much resembled the gene responses to O-1(2) reported in the Arabidopsis mutant flu. Preexposure of ch1 plants to moderately elevated light intensities eliminated photooxidative damage without suppressing O-1(2) formation, indicating acclimation to O-1(2). Substantial differences in gene expression were observed between acclimation and high-light stress: A number of transcription factors were selectively induced by acclimation, and contrasting effects were observed for the jasmonate pathway. Jasmonate biosynthesis was strongly induced in ch1 mutant plants under high-light stress and was noticeably repressed under acclimation conditions, suggesting the involvement of this hormone in O-1(2)-induced cell death. This was confirmed by the decreased tolerance to photooxidative damage of jasmonate-treated ch1 plants and by the increased tolerance of the jasmonate-deficient mutant delayed-dehiscence2