Rhizobium specificity of Trifolium ambiguum M. Bieb × T. repens L. hybrid clovers

Growth of full-sib families of an F₁ interspecific hybrid between Trifolium ambiguum M.Bieb and T. repens L, and two generations of backcross hybrids (BC₁F₂ and BC₂F₁) with T. repens as the recurrent parent, were compared to their parental species. Plants were grown in a N-free medium and inoculated with Rhizobium leguminosarum biovar trifolii rhizobia effective on T. ambiguum or T. repens. Hybridisation produced progeny that nodulated with rhizobia from either T. ambiguum or T. repens, but plant growth varied. Mean weights of T. repens and hybrids, particularly F₁ and BC₁F₂, were higher when inoculated with a mixture of strains isolated from field grown T. repens than with the New Zealand inoculant strain for T. repens. When inoculated with the mix of rhizobia from T. repens, mean weights were 242, 189, 132, 125, and 100 mg/plant for T. repens, BC₂F₁, BC₁F₂, F₁ and T. ambiguum, respectively. However, although the mean weight of BC₂F₁ lines was significantly less than T. repens, there was considerable variation in individual full-sib families indicating the potential to select within BC₂F₁ hybrids for high plant growth/symbiotic nitrogen fixation. The weight of T. ambiguumplants inoculated with the New Zealand inoculant strain for hexaploid T. ambiguum was similar to T. repens inoculated with the mix of rhizobia from T. repens (253 and 242 mg/plant, respectively). Mean fresh weights of F₁ hybrid plants were similar when inoculated with rhizobia for T. ambiguum or T. repens (125 and 130 mg/plant, respectively). However, weight of T. repens, BC₁F₂ and BC₂F₁ hybrids inoculated with rhizobia for T. ambiguum were all less than 90 mg/plant. There was a significant relationship between plant fresh weight and ethylene production. The results indicate that measuring weights of inoculated plants growing in N-free media is a rapid initial method of screening a range of plant germplasm for plant growth/symbiotic nitrogen fixation rates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of Changing Temperature on the Deterioration of Soya Beans

Deterioration rates as indicated by carbon dioxide evolution for soya bean (Glycine max L. Merr.) stored under changing temperature conditions were quantified and compared with those predicted using equations. Experiments included soya bean moisture contents of 18, 22, and 26% (wet basis), constant storage temperatures of 15, 20, 25, and 30°C, and cyclical storage temperatures that changed between 15 and 25°C and between 20 and 30°C on a 24 h basis. Also, the growth of micro-organisms was identified after 10 days from the treatments by using the pour plate method.The results indicated an increase in deterioration by increasing storage temperature and moisture content of soya bean. Equations of carbon dioxide weight versus time for each moisture content and storage temperature were fitted. The longest allowable storage time to reach 0·5% dry matter loss (1132 h) occurred at lower moisture content and lower constant storage temperature, while the shortest allowable storage time (170 h) occurred at higher moisture content and higher constant storage temperature. The allowable storage times for soya bean stored under cyclical temperatures were close to the allowable storage time for soya bean stored at a constant temperature equal to the average cyclical temperature. Microbial infection levels increased with increasing storage temperature and moisture content. The increasing rate of micro-organism growth decreased by increasing the storage temperature over 25°C. However, this increasing rate of micro-organism growth for soya bean exposed to a cyclical storage temperature was usually lower than that for soya bean held at constant storage temperatures of about 20°C (the average of 15 and 25°C) and 25°C (the average of 20 and 30°C).     

Time-resolved X-ray diffraction studies of the B in equilibrium D structural transition in the DNA double helix

Because of the relation between topology and function, there has been much interest in the structural transitions of the various conformations of DNA polymers. The x-ray fiber diffraction analysis system at the Daresbury Synchrotron Radiation Source was used to study the reversible transition between the B and D forms of the synthetic DNA poly[d(A-T)].poly[d(A-T)]. The gradual progression of conformations between these two forms indicates that the DNA double helix does not undergo a change of handedness during this transition.     

From a single-band metal to a high-temperature superconductor via two thermal phase transitions

The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at T* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (T(c)), entangled in an energy-momentum-dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.     

Using leaf tip necrosis as a phenotypic marker to predict the presence of durable rust resistance gene pair <Emphasis Type="Italic">Lr34</Emphasis>/<Emphasis Type="Italic">Yr18</Emphasis> in wheat

Fifty wheat varieties along with Jupateco-73 and Morocco were studied for the expression of leaf tip necrosis (LTN), a trait linked with the durable rust resistance gene pair Lr34/Yr18. LTN was frequent (i.e., ≥6) in nine replications of a field experiment over 3 years in 17 genotypes, and the varieties were considered positive for LTN. In molecular analyses of these varieties, having relative severity values up to 78 for yellow rust and 45 for leaf rust, the 150-bp Lr34/Yr18-linked allele was consistently amplified. Expression of LTN in six of nine replications is an appropriate threshold for predicting the presence of Lr34/Yr18 gene pair, and genotypes can be selected using this trait.     

Subcellular compartmentation of sugars in wheat leaves under the influence of salinity and boron toxicity

In this study, long-term effects of salinity and high boron (B) on subcellular distribution of sugars in wheat leaves were investigated. Four treatments with three replications of each; control, high B, sodium chloride (NaCl) and NaCl + high B, respectively were established according to completely randomized design. Plants were grown hydroponically and harvested after 6 weeks onset of experiment. NaCl treatment markedly decreased the shoot fresh and dry weight compared to high B or NaCl + high Boron. It increased the sugar concentrations in subcellular compartments, whereas decreased in NaCl + high B. Contrary, NaCl either alone or in combination with high B decreased the sugar contents in whole leaf compared to control or high B. Overall, higher concentrations of sugars were observed in symplast compared to apoplast indicating the symplast as major compartment for sugar transport. Furthermore, wheat plants accumulate sugars in subcellular compartments to maintain their growth under stress conditions.     

Metal chemistry of irrigation and drainage waters of Al-Ahsa Oasis of Saudi Arabia and its effects on soil properties

Water samples from 18 springs and 13 drainage canals and subcanals were collected from Al-Ahsa Oasis. Concentrations of total dissolved salts, Cl, SO₄ HCO₃, B, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, V, Ti, and Zn were determined. The soil salinity development (SSD), the adjusted Na ratio (adj. SAR), the adjusted Na adsorption ratio (adj. RNa), and exchangeable Na percentage (ESP) were calculated. Sodium was the most abundant cation in all water samples followed by Ca, Mg, Sr, and K in descending order. Concentrations of all other metals were below 0.1 mg L^–1. Chloride was the most abundant anion, followed by SO₄ and HCO₃ in these waters. A significant correlation (P < 0.05)=" between=" na=" and=" cl=" in=" water=" samples=" was=" found.=" thermodynamic=" calculations=" revealed=" that=" an=" appreciable=" fraction=" of=" ca=" and=" mg=" in=" spring=" and=" drainage=" waters=" were=" associated=" with=">₄ and HCO₃ ions. Calcium increased from less than 10 meq L^–1 in spring waters to > 16 meq L^–1, Mg was doubled, and Na and Cl increased several times in the drainage waters. The salinity and sodicity hazards of the spring and drainage waters were classified as C₄S₂ i.e. high salinity with medium sodicity problems.