Early angiosperm ecology: evidence from the Albian-Cenomanian of Europe

BACKGROUND AND AIMS: The mid-Cretaceous is a period of sudden turnover from gymnosperm to angiosperm-dominated floras. The aim was to investigate the fossil plant ecology in order to follow the spread of angiosperm taxa. METHODS: Floristic lists and localities from the latest Albian-Cenomanian of Europe are analysed with Wagner's Parsimony Method, a clustering method currently used in phylogeny (cladistics). KEY RESULTS: Wagner's Parsimony Method points out that (a) gymnosperms dominated brackish water-related environments while angiosperms dominated freshwater-related environments (e.g. swamps, floodplains, levees, channels), (b) angiosperms showed the highest diversity in stable, freshwater-related environments, (c) a single angiosperm, 'Diospyros' cretacea, is restricted to brackish water-related environments and (d) the families Lauraceae and Platanaceae were exclusive to disturbed, braided river environments, implying a opportunist strategy for early tree angiosperms. CONCLUSIONS: During the Mid-Cretaceous, European floras were characterized by (a) coastal gymnosperms, (b) highly diversified fluvial angiosperms and (c) the first European brackish water-related angiosperm.     

Characteristics of sun- and shade-adapted populations of an endangered plant <Emphasis Type="Italic">Primulina tabacum</Emphasis> Hance

Primulina tabacum Hance is an endangered perennial herb distributed in calcium-rich and nitrogen-limited soil of the karst limestone areas in southern China. The morphological, ultrastructural, and physiological traits were determined for P. tabacum populations growing in three different environment conditions: twilight zone of a cave (site TZ, extremely low light intensity), at a cave entrance (site EZ, low light intensity), and in an open area (site OA, high light intensity). At site OA, P. tabacum plants were exposed to high light (635 μmol m⁻² s⁻¹ of mean daily photosynthetically active radiation) with drought stress, and expressed traits to minimize light capture and water loss. Compared to plants at sites EZ and TZ, those at site OA had thicker leaves with higher densities of stomata and pubescence, higher palisade/spongy ratio, higher light-saturated rate of net photosynthetic rate (P _max), higher biomass, higher non-photochemical quenching coefficient (NPQ), and higher light saturation point (LSP) but fewer grana per chloroplast and less thylakoid stacking per granum. In contrast, P. tabacum growing at the cave vicinities: EZ (mean daily irradiance 59 μmol m⁻² s⁻¹) and TZ (mean daily irradiance 11 μmol m⁻² s⁻¹) showed typical shade-adapted characteristics for optimum light capture. The presence of sun- and shade-adapted characteristics indicates that P. tabacum has different strategies to cope with different environments but whether these strategies reflect genetic selection or phenological plasticity is yet to be determined. Such variability in physiological and morphological traits is important for the survival of P. tabacum in heterogeneous light conditions.     

Nuclear localization of PAPS synthetase 1: a sulfate activation pathway in the nucleus of eukaryotic cells.

Sulfation is a major modification of many molecules in eukaryotes that is dependent on the enzymatic synthesis of an activated sulfate donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS). While sulfate activation has long been assumed to occur in the cytosol, we show in this study that human PAPS synthetase 1 (PAPSS1), a bifunctional ATP sulfurylase/adenosine 5'-phosphosulfate (APS) kinase enzyme sufficient for PAPS synthesis, accumulates in the nucleus of mammalian cells. Nuclear targeting of the enzyme is mediated by its APS kinase domain and requires a catalytically dispensable 21 amino acid sequence at the amino terminus. Human PAPSS1 and Drosophila melanogaster PAPSS localize to the nucleus in yeast and relieve the methionine auxotrophy of ATP sulfurylase- or APS kinase-deficient strains, suggesting that PAPSS1 is fully functional in vivo when targeted to the nucleus. A second PAPS synthetase gene, designated PAPSS2, has recently been described, mutations of which are responsible for abnormal skeletal development in human spondyloepimetaphyseal dysplasia and murine brachymorphism. We found that PAPSS2, which localizes to the cytoplasm when ectopically expressed in mammalian cells, is relocated to the nucleus when coexpressed with PAPSS1. Taken together, these results indicate that a sulfation pathway might exist in the nucleus of eukaryotic cells. -Besset, S., Vincourt, J.-B., Amalric, F., Girard, J.-P. Nuclear localization of PAPS synthetase 1: a sulfate activation pathway in the nucleus of eukaryotic cells.     

Une nouvelle fonction pour la transferrine exprimée par le testicule

In men, oligozoospermia corresponds with a low level of transferrin in semen. Transferrin appears to be a relevant indicator of gonadal function. Transferrin expression in normal testes is perfectly controlled. Transferrin contributes to iron transport. However, recent results show the existence of a dimeric form, which acts as a powerful regulator of phagocytosis of residual bodies by Sertoli cells. A disturbance of this new highlighted function may account for some forms of oligozoospermia.