No abstract

Complexes of NaDNA with bipyridyl-͑ethylenediamine͒platinum͑II͒ ͑abbreviated ͓(bipy)Pt(en)͔ 2ϩ ) in solid, oriented films, prepared with a wet-spinning method, have been studied using x-ray diffraction, elastic neutron scattering, two-dimensional magic-angle-spinning nuclear magnetic resonance ͑NMR͒, infrared ͑IR͒ linear dichroism, and IR absorption. All of these experiments indicate that the DNA in this complex is in the B conformation. The neutron diffraction experiments reveal that the rise per residue is 3.31 Å, indicating that the ͓(bipy)Pt(en)͔ 2ϩ molecular ion causes a small distortion of the B conformation. The neutron data in the direction perpendicular to the helical axis are consistent with a centered orthorhombic unit cell with a ϭ22.65 Å and bϭ32.2 Å. The NMR and IR experiments show that the orientation of phosphate groups in the DNA•͓(bipy)Pt(en)͔ 2ϩ complex is the same as that observed for pure DNA in the B conformation. The IR experiments also show that the ͓(bipy)Pt(en)͔ 2ϩ molecular ion stabilizes the B conformation of DNA down to 59% relative humidity, a low water activity. Mechanochemical experiments on wet-spun NaDNA fibers in 68% ethanol with and without ͓(bipy)Pt(en)͔ 2ϩ reveal a 9% elongation of the DNA fibers as the complex is formed.

Effects of unfavourable environmental conditions (stresses) induce stressor specific and unspecific shortand long-term responses in plants. Long-term responses depend on intensity and duration of the stress. Short-term effects comprise the accumulation of reactive oxygen species (ROS), membrane damages by the oxidation of fatty acids, and the release of amino alcohols. They can incite higher stress tolerance in plants.In the present study, shoots of barley (Hordeum vulgare) were pre-treated with 2-aminoethanol, and, 2 days later, with the oxidative stress inducing herbicide, paraquat. Pre-treatments with 2-aminoethanol increased the stress tolerance in barley by the stabilization of the cell membranes, the enhanced production of superoxide dismutase and catalase, and the stimulation of glutathione metabolism (GSH, GST). These mechanisms of stress tolerance activation by 2-aminoethanol are discussed.

We have studied the catalysis of the exchange of the hydrogen-bonded NH-N protons of the short DNA helix (d-CCAAGCTTGG)2 by phosphate addition. The NH exchange rates were monitored by the line widths of the corresponding NH resonances in the 1H nmr spectra. The exchange catalyst phosphate is most effective on the exchange rate of the terminal CG1 base pairs. However, all internal base pairs are also moderately affected by phosphate which suggests an exchange mechanism governed by a fast equilibrium between opened and closed states of the duplex. Within the limits of error the same effectiveness of phosphate on the exchange rate of all internal NH-N protons has been observed. With the exception of the terminal base pairs, no sequence and/or position specificity of the exchange rates of the NH-N protons of the base pairs has been found.

No abstract