S. Waplak

Metabolic and ultrastructural responses of lupine embryo axes to sugar starvation

Embryo axes isolated from germinating lupine seeds were cultivated in vitro for 24-96 h over media containing either 60 mmol/L sucrose or no sucrose. Ultrastructural studies showed that large vacuoles were accumulating in a central region of primary parenchyma cells in sucrose starved lupine embryo axes, whereas cytoplasm along with organelles were forced to a periphery of the cells. We suggest that the autolysis of cytoplasmic proteins contributes to the accumulation of the vacuoles and this suggestion is consistent with the results of the characterisation of protein content. The level of cytosolic proteins was reduced by 50% and the activity of cytosolic marker enzyme, PEP carboxylase, was reduced by 46% in starved embryos as compared to control. The mitochondria from starved tissues were not degraded. The level of mitochondrial proteins was reduced by only 10% and the activity of mitochondrial NAD-isocitrate dehydrogenase decreased by 8% as a result of starvation. As demonstrated by the results of Percoll density gradient centrifugation, sucrose starvation caused an increase of 49% in many of the higher density mitochondria fractions, whereas many of the lower density mitochondria fractions were decreased by 33%. The samples of mitochondria from starved embryo axes were determined to have higher respiration activity in the presence of glutamate and malate as compared to control samples. EPR-based analyses of free radicals showed the presence of free radicals with a signal at g = 2.0060 in embryo axes. The level of the radical was two times higher in sucrose-starved embryo axes than in control (the level of this radical increased in senescing plant tissues as well). The results of EPR-based quantitation of Mn2+ ions revealed that the level was a few times higher in starved material than in control. Starved embryo axes, however, do possess a number of adaptive mechanisms protecting them from oxidative damage. Densitometric analyses of gels revealed an increase in the activity of SOD in sugar-starved embryos, whereas CAT and POX activities were lower in axes grown without sucrose as compared to control. Superoxide dismutase, catalase and peroxidase zymogram analyses showed that synthesis of new isoforms was not induced by sugar starvation. An accumulation of phytoferritin was found in plastids of sucrose starved embryos. These results are discussed in relation to the metabolic changes observed in senescing plant tissues.

Dielectric properties of TGS and TGFB monocrystals under high pressure

The Ps, Ec and Tc under high pressure in TGS and TGFB crystals in the range up to 25 kbar were investigated. At pressures up to 10-14 kbar the shift of the Curie point is linear with dTc/dp = 2.4°K/kbar. At higher pressures a nonlinear increase in Tc has been observed. It is associated with hindered rotation of the NH3 groups. The effect of pressure on the spontaneous polarization is greater than that resulting from a single displacement of TC vs. p.

Low temperature short-range ordering caused by Mn2 + doping of Rb3H(SO4)2

The low temperature behaviour of Rb₃H(SO₄)₂ and Rb₃D(SO₄)₂ and their doped analogues was investigated by means of their dielectric response. Electron paramagnetic resonance was used to control the impurity concentration. Influence of different admixtures on ferroic properties is discussed. It has been shown that an appropriately chosen impurity in doped Rb₃H(SO₄)₂ can lead to a short-range ordering similar to that observed for doped incipient ferroelectric-like SrTiO₃ and KTaO₃.

Crystal structure and phase transitions in the new crystals of [(CH3)2NH2]2CuCl4[(CH3)2NH2]Cl

Crystals grown from a solution of dimethylammonium and copper chlorides are studied using electron paramagnetic resonance (EPR) and X-ray diffraction. The dielectric properties of the crystals grown are measured. It is established that the crystals have the composition [(CH3)2NH2]2CuCl4[(CH3)2NH2]Cl and, in phase I at room temperature, are described by the orthorhombic space group Pna21 with the unit cell parameters a = 11.338 Å, b = 9.981 Å, and c = 15.675 Å. At temperatures of 279 K and 253 K, the crystals undergo jumpwise phase transitions into the incommensurate modulated ferroelectric phase II and commensurate modulated phase III, respectively.

The EPR evidence of local hydrogen bond distortion evoked by ions in crystals

An investigation of the influence of the proton subsystem on the EPR spectra of ions in is performed. The EPR superhyperfine structure from protons and their temperature dependences manifest the existence of asymmetrical configurations of protons at low temperatures. The preserving of the double-minimum character of proton potential on bonds in the near vicinity of ions is realized. It is suggested to be caused by redistribution of electron charges.

Preparation, crystal structure and characterization of C60·2[(Ph3P)AuCl]

Abstract Investigations of crystal structure, infrared spectra and electron spin resonance of the complex of the fullerene C60 with chloro(triphenylophosphine)gold have been performed. It was stated that the C60·2[(Ph3P)AuCl] complex is a molecular crystal in which van der Waals interactions are predominant. The electron spin resonance (ESR) spectrum was discussed and explained. A phase transition at about 195–200 K was suggested.

A study of the x-irradiated crystal by EPR in the 80 - 415 K temperature range

The EPR spectra of the x-irradiated fast proton conductor were investigated in the temperature range of 80 - 415 K. Two kinds of paramagnetic centres with different proton configurations below about 370 K and freeze-out behaviour of one of them below about 200 K were observed. The role of acid proton dynamics with respect to the glassy-like transition is discussed.

Electric modulation in epr as a new method for the study of ferroelectrics

Abstract A new experimental method is presented for a selective study of the electric field effects in the EPR spectra obtained with the electric modulation. The electric modulation (EM) was applied either jointly with the magnetic modulation (MM) as EMM EPR or as EM EPR where the electric modulation alone was used. The application of the method to a study of ferroelectric crystals containing paramagnetic centres, has been discussed.

Electron paramagnetic resonance investigation of K3H(SO4)2 proton conductor doped with Cr5+ ion

Abstract The proton arrangement around SO4 units in K3H(SO4)2 (KHS) was studied in detail by X-band CW EPR spectra of CrO43− paramagnetic centre incorporated into KHS during the crystal growth process. The EPR data prove the theoretical model of coherent motion of protons and SO4 units at the fast-proton conducting phase proposed by Ito and Kamimura.

Dielectric and EPR measurements of the deuterated glass D-RADA x=0.46

Abstract The results of the complex dielectric permittivity measurements and the spin-lattice relaxation times of the deuterated glass D-RADA x = 0.46, by the dielectric and EPR techniques are reported. The transition from paraelectric to antiferroelectric phase is detected at TN = 162 K. Below 90 K the dispersion of the complex dielectric permittivity was detected. The shape of the temperature dependence of the imaginary part of the dielectric permittivity was analyzed. This analysis shows the existence of two relaxation phases forming among the antiferroelectric domains, described by Arrhenius equation, and the glass state appears after the antiferroelectric ordering has been destroyed. The dielectric results are confirmed by the spin-lattice relaxation times data.