No abstract

We investigate the supercurrent through a quantum dot for the whole range of couplings using the numerical renormalization group method. We find that the Josephson current switches abruptly from a -to a 0-phase as the coupling increases. At intermediate couplings the total spin in the ground state depends on the phase difference between the two superconductors. Our numerical results can explain the crossover in the conductance observed experimentally by Buitelaar et al.

One of the actual challenges of spintronics is the realization of a spin transistor allowing control of spin transport through an electrostatic gate. In this paper, we report on different experiments which demonstrate gate control of spin transport in a carbon nanotube connected to ferromagnetic leads. We also discuss some theoretical approaches which can be used to analyse spin transport in these systems. We emphasize the roles of the gate-tunable quasi-bound states inside the nanotube and the coherent spin-dependent scattering at the interfaces between the nanotube and its ferromagnetic contacts.

A comparative proteomic approach has been adopted in combination with physiological and biochemical analysis of tomato leaves responding to waterlogging stress. Waterlogging resulted in increases of relative ion leakage, lipid peroxidation and in vivo H2O2 content, whereas the chlorophyll content was decreased. Histocytochemical investigations with 3,3'-diaminobenzidine to localize H2O2 and Evans blue to detect dead cells suggested that oxidative stress has a significant role to leaf senescence. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the most abundant leaf protein, was successfully reduced from the samples by a fractionation method based on 15% polyethylene glycol (PEG). Elimination of Rubisco was further confirmed by Western blot analysis. To elucidate the temporal changes of the protein patterns in tomato leaves, the total soluble and the PEG-fractionated proteins were separated by two-dimensional electrophoresis (2-DE) and visualized by Coomassie Brilliant Blue staining. A total of 52 protein spots were differentially expressed, wherein 33 spots were identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry or electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis. The identified proteins are involved in several processes, i.e. photosynthesis, disease resistance, stress and defense mechanisms, energy and metabolism and protein biosynthesis. Results from 2-DE analysis, combined with immunoblotting clearly showed that the fragments of Rubisco large subunit were significantly degraded. This could result from a higher production of reactive oxygen species in leaves under waterlogging stress. Furthermore, four differentially accumulated proteins were analyzed at the mRNA level, confirming the differential gene expression levels and revealing that transcription levels are not always concomitant to the translation level. A number of novel proteins were differentially expressed or appeared only in the PEG-fractionated protein samples, indicating that PEG fractionation system can be used as a versatile protein fractionation technique in proteomic analysis to identify novel or low-abundant proteins from all kinds of plant species.

Positive selection of transgenic plants is essential during plant transformation. Thus, strong promoters are often used in selectable marker genes to ensure successful selection. Many plant transformation vectors, including pPZP family vectors, use the 35S promoter as a regulatory sequence for their selectable marker genes. We found that the 35S promoter used in a selectable marker gene affected the expression pattern of a transgene, possibly leading to a misinterpretation of the result obtained from transgenic plants. It is likely that the 35S enhancer sequence in the 35S promoter is responsible for the interference, as in the activation tagging screen. This affected expression mostly disappeared in transgenic plants generated using vectors without the 35S sequences within their T-DNA region. Therefore, we suggest that caution should be used in selecting a plant transformation vector and in the interpretation of the results obtained from transgenic approaches using vectors carrying the 35S promoter sequences within their T-DNA regions.