15 research outputs found
The quest for companions to post-common envelope binaries: I. Searching a sample of stars from the CSS and SDSS
As part of an ongoing collaboration between student groups at high schools
and professional astronomers, we have searched for the presence of
circum-binary planets in a bona-fide unbiased sample of twelve post-common
envelope binaries (PCEBs) from the Catalina Sky Survey (CSS) and the Sloan
Digital Sky Survey (SDSS). Although the present ephemerides are significantly
more accurate than previous ones, we find no clear evidence for orbital period
variations between 2005 and 2011 or during the 2011 observing season. The
sparse long-term coverage still permits O-C variations with a period of years
and an amplitude of tens of seconds, as found in other systems. Our
observations provide the basis for future inferences about the frequency with
which planet-sized or brown-dwarf companions have either formed in these
evolved systems or survived the common envelope (CE) phase.Comment: accepted by A&
RPE, a plant gene involved in early developmental steps of nematode feeding cells.
Sedentary plant-parasitic nematodes are able to induce the redifferentiation of root cells into multinucleate nematode feeding sites (NFSs). We have isolated by promoter trapping an Arabidopsis thaliana gene that is essential for the early steps of NFS formation induced by the root-knot nematode Meloidogyne incognita. Its pattern of expression is similar to that of key regulators of the cell cycle, but it is not observed with the cyst nematode. Later in NFS development, this gene is induced by both root-knot and cyst nematodes. It encodes a protein similar to the D-ribulose-5-phosphate 3-epimerase (RPE) (EC 5.1.3.1), a key enzyme in the reductive Calvin cycle and the oxidative pentose phosphate pathway (OPPP). Quantitative RT-PCR showed the accumulation of RPE transcripts in potato, as in Arabidopsis NFS. Homozygous rpe plants have a germination mutant phenotype that can be rescued in dwarf plants on sucrose-supplemented medium. During root development, this gene is expressed in the meristems and initiation sites of lateral roots. These results suggest that the genetic control of NFSs and the first stages of meristem formation share common steps and confirms the previous cytological observations which indicate that root cells undergo metabolic reprogramming when they turn into NFSs