Evidence of parasitic Oomycetes (Peronosporomycetes) infecting the stem cortex of the Carboniferous seed fern <i>Lyginopteris oldhamia</i>

Thin sections of petrified fossils made during the latter part of the nineteenth and early twentieth centuries to investigate the internal tissue systems of plants now provide an important new source of information on associated micro-organisms. We report a new heterokont eukaryote (Combresomyces williamsonii sp. nov.) based on exquisitely preserved fossil oogonia, antheridia and hyphae from the Carboniferous (Pennsylvanian: Bashkirian stage) of UK. The structure of the oogonia and antheridia and features observed within the hyphae demonstrate a relationship with Oomycetes (Peronosporomycetes). The fossil micro-organism was documented in situ in petrified stem cortex and rootlets of the extinct seed fern Lyginopteris oldhamia (Pteridospermales). The main observed features point towards a pythiaceous Oomycete but links to biotrophic Albuginales or Peronosporaceae cannot be ruled out owing to the observation of a possible haustorium. Our study provides the earliest evidence for parasitism in Oomycetes

Information biochimique donnée par les acides aminés libres du phylloplan

National audienc

Chemicals on the leaf surface, information about the plant available to insects

International audienc

Chemicals on the leaf surface, information about the plant available to insects

International audienc

Electronic spectra of the amorphous Au/Si interface

Auger and Electron Loss Spectra (ELS) have been measured on Au deposited on the (111) Si surface at room temperature. The absence of LEED pattern and a structural analysis by Auger technique clearly show an amorphous surface composition close to the eutectic composition Au.81Si.19 irrespective of the amount of Au deposited. This is also confirmed by the evolution of ELS spectra during the growth process and during a subsequent sputtering. Evidence is found for the formation on top of the Si substrate of 1. a diffuse interface of ~ 20 Å thickness, 2. a pure Au film and 3. an eutectic amorphous surface. The stability of the surface composition is discussed using molecular dynamics calculations. The parameters of the model have been deduced from thermodynamical data on the Au-Si system. They reflect a strong attractive hetero-atomic interaction. The calculations show that the surface with eutectic concentration is in equilibrium with a pure gold substrate

ELECTRONIC SPECTRA OF THE AMORPHOUS AuSi INTERFACE

Auger and Electron Loss Spectra (ELS) have been measured on Au deposited on the (111) Si surface at room temperature. The absence of LEED pattern and a structural analysis by Auger technique clearly show an amorphous surface composition close to the eutectic composition Au.81Si.19 irrespective of the amount of Au deposited. This is also confirmed by the evolution of ELS spectra during the growth process and during a subsequent sputtering. Evidence is found for the formation on top of the Si substrate of 1. a diffuse interface of ~ 20 Å thickness, 2. a pure Au film and 3. an eutectic amorphous surface. The stability of the surface composition is discussed using molecular dynamics calculations. The parameters of the model have been deduced from thermodynamical data on the Au-Si system. They reflect a strong attractive hetero-atomic interaction. The calculations show that the surface with eutectic concentration is in equilibrium with a pure gold substrate