A Determinant of Substrate Specificity Predicted from the Acyl-Acyl Carrier Protein Desaturase of Developing Cat's Claw Seed1

Cat's claw (Doxantha unguis-cati L.) vine accumulates nearly 80% palmitoleic acid (16:1Δ9) plus cis-vaccenic acid (18:1Δ11) in its seed oil. To characterize the biosynthetic origin of these unusual fatty acids, cDNAs for acyl-acyl carrier protein (acyl-ACP) desaturases were isolated from developing cat's claw seeds. The predominant acyl-ACP desaturase cDNA identified encoded a polypeptide that is closely related to the stearoyl (Δ9–18:0)-ACP desaturase from castor (Ricinis communis L.) and other species. Upon expression in Escherichia coli, the cat's claw polypeptide functioned as a Δ9 acyl-ACP desaturase but displayed a distinct substrate specificity for palmitate (16:0)-ACP rather than stearate (18:0)-ACP. Comparison of the predicted amino acid sequence of the cat's claw enzyme with that of the castor Δ9–18:0-ACP desaturase suggested that a single amino acid substitution (L118W) might account in large part for the differences in substrate specificity between the two desaturases. Consistent with this prediction, conversion of leucine-118 to tryptophan in the mature castor Δ9–18:0-ACP desaturase resulted in an 80-fold increase in the relative specificity of this enzyme for 16:0-ACP. The alteration in substrate specificity observed in the L118W mutant is in agreement with a crystallographic model of the proposed substrate-binding pocket of the castor Δ9–18:0-ACP desaturase.

Abundance of palynomorphs and dinoflagellate stratigraphy of ODP Hole 184-1148A, South China Sea

Dinoflagellate stratigraphy is described for the section from 364.75 to 843.85 meters below seafloor (mbsf) at Site 1148 (Sections 184-1148A-40X-1 through 76X-6 and 184-1148B-39X-CC through 56X-1) in the South China Sea. Two assemblage zones and two subzones are defined, based on characteristics of the assemblages and lowest/highest occurrences of some key species. These are the Cleistosphaeridium diversispinosum Assemblage Zone (Zone A; Oligocene), with the Enneadocysta pectiniformis Subzone (Subzone A-1) and the Cordosphaeridium gracile Subzone (Subzone A-2), and the Polysphaeridium zoharyi Assemblage Zone (Zone B; early Miocene). The highest concurrent occurrence of Enneadocysta arcuata, Eneadocysta multicornuta, Homotryblium plectilum, and Homotryblium tenuispinosum delineates the upper boundary of Zone A, which appears to mark a hiatus. Subzone A-1 is of early Oligocene age, as evidenced by the highest occurrences of E. pectiniformis and Phthanoperidinium amoenum at the upper boundary of the subzone. Subzone A-2 is of late Oligocene age based on the highest occurrences of C. gracile and Wetzeliella gochtii close to the upper boundary of the subzone and the occurrence of Distatodinium ellipticum and Membranophoridium aspinatum within the subzone. Zone B is dated as early Miocene based on the lowest occurrences of Cerebrocysta satchelliae, Hystrichosphaeropsis obscura, Melitasphaeridium choanophorum, Membranilarnacia? picena, and Tuberculodinium vancampoae within the zone. The present assemblage zones/subzones are correlative to various degrees with coeval zones/assemblages from areas of high to low latitudes in terms of common key species. We have compared the species content of the assemblage Zones A and B, and the subzones A-1 and A-2, with coeval assemblage(s)/zone(s) described from many, often widely distant, high- and low-latitude regions of the world. These comparisons show that, to various degrees and aside from a number of key species, the coordinated presence of certain important species may also help to assign an age to a given assemblage.

Variation in oxygen isotope fractionation during cellulose synthesis: intramolecular and biosynthetic effects

The oxygen isotopic composition of plant cellulose is commonly used for the interpretations of climate, ecophysiology and dendrochronology in both modern and palaeoenvironments. Further applications of this analytical tool depends on our in-depth knowledge of the isotopic fractionations associated with the biochemical pathways leading to cellulose. Here, we test two important assumptions regarding isotopic effects resulting from the location of oxygen in the carbohydrate moiety and the biosynthetic pathway towards cellulose synthesis. We show that the oxygen isotopic fractionation of the oxygen attached to carbon 2 of the glucose moieties differs from the average fractionation of the oxygens attached to carbons 3–6 from cellulose by at least 9%, for cellulose synthesized within seedlings of two different species (Triticum aestivum L. and Ricinus communis L.). The fractionation for a given oxygen in cellulose synthesized by the Triticum seedlings, which have starch as their primary carbon source, is different than the corresponding fractionation in Ricinus seedlings, within which lipids are the primary carbon source. This observation shows that the biosynthetic pathway towards cellulose affects oxygen isotope partitioning, a fact heretofore undemonstrated. Our findings may explain the species-dependent variability in the overall oxygen isotope fractionation during cellulose synthesis, and may provide much-needed insight for palaeoclimate reconstruction using fossil cellulose.

Lower Albian benthic foraminifera

The Early Albian Oceanic Anoxic Event 1b (OAE 1b) black shale is interrupted by one or more ventilation events that display significant changes in benthic and planktic populations. Within the OAE 1b sections studied, at ODP Site 1049, DSDP Site 545, and the Vocontian Basin, the benthic foraminiferal repopulation events last between ~500 and ~1,250 years and occur with a cyclicity of approximately 5.7 kyr. This period may represent an amplitude modulation of the precessional cycle. The OAE 1b sections from the marginal setting of the Vocontian Basin exhibit up to eight repopulation events. In contrast, there is only one repopulation event identified in the Atlantic OAE 1b sections from the Mazagan Plateau (DSDP 545) and Blake Nose (ODP 1049). Within the margin of dating uncertainties, this supraregional repopulation event occurred synchronously in the Vocontian Basin and the Atlantic Ocean. While the OAE 1b black shale formed under extremely warm and humid conditions, the repopulation events occurred during intervals of short-term cooling and reduced humidity at deep-water formation sites. The resulting increase in evaporation led to enhanced formation of low-latitude deep water, thus improving the ventilation of the sea floor.

Juniperus navicularis - a study of Portuguese population structure and fitness

Juniperus navicularis Gand. is a dioecious endemic conifer that constitutes the understory of seaside pine forests in Portugal, areas currently threatened by increasing urban expansion. The aim of this study is to assess the conservation status of previously known populations of this species located on its core area of distribution. The study was performed in south-west coast of Portugal. Three populations varying in size and pine density were analyzed. Number of individuals, population density, spatial distribution and individual characteristics of junipers were estimated. Female cone, seed characteristics and seed viability were also evaluated. Results suggest that J. navicularis populations are vulnerable because seminal recruitment is scarce, what may lead to a reduction of genetic variability due solely to vegetative propagation. This vulnerability seems to be strongly determined by climatic constraints toward increasing aridity. Ratio between male and female shrubs did not differ from 1:1 in any population. Deviations from 1:1 between mature and non-mature plants were found in all populations, denoting population ageing. Very low seed viability was observed. A major part of described Juniperus navicularis populations have disappeared through direct habitat loss to urban development, loss of fitness in drier and warmer locations and low seed viability. This study is the first to address J. navicularis conservation, and represents a valuable first step toward this species preservation. 

Desenvolvimento de um novo processo para a produção de biodiesel etílico de mamona

No presente trabalho estudou-se a produção de ésteres etílicos de ácido graxo de Ricinus communis L. através da tranesterificação alcalina do óleo de mamona com etanol. Esta metodologia foi adotada para determinar as melhores condições para a produção de biodiesel a partir de óleo de mamona usando o mínimo de operações unitárias com benefícios do ponto de vista econômico e de produção de efluentes. Para a obtenção dos ésteres etílicos através do processo de transesterificação (etapa 1) utilizou-se como catalisador 1% de NaOH com etanol em uma razão molar de 6:1 seguido da adição de ácido sulfúrico. Após, a reação de esterificação (etapa 2) dos ácidos graxos contidos no biodiesel foi realizada visando reduzir o índice de acidez da amostra, ficando em torno de 2 mg de KOH/g. A quebra in situ dos sabões (provenientes da reação paralela de saponificação do triglicerídeo) pela adição de ácido sulfúrico ao meio reacional foi bem sucedida melhorando a separação dos FAEEs do glicerol. O processo em duas etapas transesterificação/esterificação apresentou boa conversão para os ésteres etílicos, diminuindo o índice de acidez e atingindo as especificações para glicerina total e livre. O biodiesel proveniente do óleo de mamona foi composto de 90,6% ácido ricinoléico (C18:1, OH), 3,2% ácido oléico (C18:1), 4,5% ácido linoléico (C18:2), 0,7% ácido esteárico (C18:0), 1,0% ácido palmítico (C16:0), triacilgliceróis (TGs, 0%), diacilgliceróis (DGs, 0,37%) monoacilgliceróis (MGs, 0,46%) e glicerol livre (0,25%) após o processo em duas etapas transesterificação/esterificação. O processo em duas etapas foi muito importante para determinar a integralidade da reação no rendimento do produto. Os resultados demonstram que o procedimento desenvolvido para a produção de FAEEs em escala de laboratório pode ser escalonado para uma planta piloto.