Growth responses of selected clones of birch (Betula pendula roth.,B. pubescens Ehrh.) and willow (Salix caprea L.,S. cinerea L.) to nitrogen in solution culture

Summary Growth of selected clones of birch and willow obtained from nitrogen deficient soils was compared with that of unselected controls in pot experiments using three levels of nitrogen. Unselected controls of both genera continued shoot growth, albeit very slowly, with a very low level of nitrogen (5 ppm), while selected clones of birch grew significantly more than the controls. Selected clones of willow, on the other hand, ceased shoot growth after 10 weeks with this low nitrogen treatment. Nevertheless, they remained healthy, their leaves containing similar concentrations of nitrogen to those of the plants which continued stem growth throughout the experiment. Furthermore, they had very high root: shoot ratios compared with those of control willows and both selected and unselected birch. The two genera may have developed different mechanisms for tolerating low nitrogen, birch producing a small, relatively efficient root system; willow a larger but less efficient one. Both appear equally effective in ensuring survival on low-nitrogen sites in the field since all the selected clones were obtained from such sites and have survived well in field trials on similar sites. Both birch and willow responded toincreased nitrogen availability with increasing shoot growth and a relative decline in root growth. However, whereas in willow the unselected plants responded significantly more than selected clones, a similar but less markeddifference was found in birch. It appears that in both genera, as in herbaceous plants originating from nitrogen deficient sites, selected clones are less able to respond to increasing nitrogen supply than control plants from more fertile habitats. Attempts to correlate the response of the selected clones to nitrogen in this experiment with that to added nitrogen fertilizer in field trials has been unsuccessful. Further work is required to determine the importance of the many interacting factors which influence the response of young trees to nitrogen under the unusual field conditions associated with restored mineral workings.     

Phosphorus requirements of the wheat plant in various stages of its life cycle

Summary In pot experiments root growth and P uptake were found to precede shoot growth. The high rate of P uptake in the early stages of the life cycle is not an expression of luxury consumption but reflects a high P requirement in plants. Plants cultivated in nutrient solutions with different P concentrations during various stages of development showed that a high P supply (1 ppm) between Feekes stages 6 and 9 (30 days) caused a higher grain yield than the same P concentration between Feekes stages 11 and 17 (30 days). The early applied P caused a high number of fertile ears per area, a high number of grains per ear, and a high P pool in vegetative parts. The latter could be mobilized during the grain-filling period. Therefore, for high grain yields soil and fertilizers have to meet the high P requirement (about 20 g P/m root · day) in an early stage of plant growth. During the grain filling period the P supply can be much lower.     

Lunasin is a redox sensitive intrinsically disordered peptide with two transiently populated α-helical regions

Lunasin is a 43 amino acid peptide with anti-cancer, antioxidant, anti-inflammatory and cholesterol-lowering properties. Although the mechanism of action of lunasin has been characterized to some extent, its exact three-dimensional structure as well as the function of the N-terminal sequence remains unknown. We established a novel method for the production of recombinant lunasin that allows efficient isotope labeling for NMR studies. Initial studies showed that lunasin can exist in a reduced or oxidized state with an intramolecular disulfide bond depending on solution conditions. The structure of both forms of the peptide at pH 3.5 and 6.5 was characterized by CD spectroscopy and multidimensional NMR methods. The data indicate that lunasin belongs to the class of intrinsically disordered proteins. The analysis of secondary structure propensities indicates the presence of two helical regions and an extended (beta strand) conformation at the C-terminus. We hypothesize that the transient secondary structure elements could be stabilized upon interaction with the histones H3 and H4. The newly discovered redox properties of lunasin could explain its antioxidant and anti-inflammatory activity.     

Origin of the regioselectivity in an intramolecular nucleophilic addition to arene chromium tricarbonyl complexes

The source of the regioselectivity in the intramolecular nucleophilic addition of nitrile-stabilized carbanions to arene chromium tricarbonyl complexes was investigated for seven different substitution patterns on the arenes. All of the arenes are 1,4-dioxygenated and the substitution varies in the oxygen substituent and in the substituents of the arene carbons (hydrogen and alkyl). The regioselectivity is correlated with the preferred conformations of the chromium tricarbonyl group which in turn was determined by solution and solid-state ¹³C NMR spectroscopy, ¹H NMR spectroscopy in solution as well as X-ray diffraction. In the four complexes analyzed by X-ray diffraction and the three complexes analyzed by solid-state ¹³C NMR spectroscopy, there was only one complex where it was found that the preferred conformation of the -Cr(CO)₃ is different in solution than it is in the solid-state.     

The stability of intramolecular DNA G-quadruplexes compared with other macromolecules

DNA quadruplexes are often conceived as very stable structures. However, most of the free energy of stabilization derives from specific ion binding via inner sphere coordination of the GO6 of the guanine residues comprising the basic quartet. When compared with other nucleic acid structures such as DNA or RNA duplexes and hairpins, or proteins of the same number of atoms, metal-coordinated intramolecular quadruplexes are found to be of comparable or lower thermodynamic stability under similar solution conditions. Furthermore, intramolecular quadruplexes are actually less stable kinetically, than DNA duplexes or hairpins of the same size.     

Syntheses of oligomannosides in solution and on a soluble polymer support: a comparison

The alpha-(1-->6)-linked and the alpha-(1-->2)-linked linear mannotetraose glycosides and, respectively, and the branched mannopentaoside [R=CH2(CH2)2CH2Cl] were synthesised by conventional methods in solution, using trichloroacetimidate donors, and the products were obtained in 39%, 42% and 40% overall yield, respectively. For comparative purposes, the same two linear tetrasaccharides were prepared by use of MPEG as a soluble polymer support, the yields being 34% and 14%, respectively. An attempted MPEG-supported synthesis of the branched pentasaccharide was unsuccessful. The merits and shortcomings of oligosaccharide syntheses on MPEG are discussed.     

NMR solution structure of BmK-betaIT, an excitatory scorpion beta-toxin without a 'hot spot' at the relevant position

BmK-betaIT (previously named as Bm32-VI in the literature), an excitatory scorpion beta-toxin, is purified from the venom of the Chinese scorpion Buthus martensii Karsch. It features a primary sequence typical of the excitatory anti-insect toxins: two contiguous Cys residues (Cys37-Cys38) and a shifted location of the fourth disulfide bridges (Cys38-Cys64), and demonstrates bioactivity characteristic of the excitatory beta-toxins. However, it is noteworthy that BmK-betaIT is not conserved with a glutamate residue at the preceding position of the third Cys residue, and is the first example having a non-glutamate residue at the relevant position in the excitatory scorpion beta-toxin subfamily. The 3D structure of BmK-betaIT is determined with 2D NMR spectroscopy and molecular modeling. The solution structure of BmK-betaIT is closely similar to those of BmK IT-AP and Bj-xtrIT, only distinct from the latter by lack of an alpha(0)-helix. The surface functional patch comparison with those of BmK IT-AP and Bj-xtrIT reveals their striking similarity in the spatial arrangement. These results infer that the functional surface of beta-toxins is composed of two binding regions and a functional site. The main binding site is consisted of hydrophobic residues surrounding the alpha(1)-helix and its preceding loop, which is common to all beta-type scorpion toxins affecting Na(+) channels. The second binding site, which determines the specificity of the toxin, locates at the C-terminus for excitatory insect beta-toxin, while rests at the beta-sheet and its linking loop for anti-mammal toxins. The functional site involved in the voltage sensor-trapping model, which characterizes the function of all beta-toxins, is the negatively charged residue Glu15.     

The solution structure of bis(acetylacetonato)oxovanadium(IV)

The behaviour of the bis-chelated oxovanadium(IV) complexes formed by acetylacetone (acac) and five of its derivatives was re-examined through a combination of spectroscopic methods in different solvents. It has been found that the complexes are penta-coordinated with a geometry close to the square pyramid and maintain in solution the same structure as in the solid state. The results rule out a cis-trans isomerism of the species VOL₂S (L = acac or derivative, S = solvent) in solution. Depending on the coordinating ability of the solvent a sixth molecule can be bound, more or less strongly, to the free axial position of the complexes. The combined application of the electronic absorption and IR spectroscopies allows to establish if the complexes in solution are penta- or hexa-coordinated.     

Complex formation between calmodulin and a peptide from the intracellular loop of the gap junction protein connexin43: Molecular conformation and energetics of binding

Gap junctions are formed by a family of transmembrane proteins, connexins. Connexin43 is a widely studied member of the family, being ubiquitously expressed in a variety of tissues and a target of a large number of disease mutations. The intracellular loop of connexin43 has been shown to include a calmodulin binding domain, but detailed 3-dimensional data on the structure of the complex are not available. In this study, we used a synthetic peptide from this domain to reveal the conformation of the calmodulin-peptide complex by small angle X-ray scattering. Upon peptide binding, calmodulin lost its dumbbell shape, adopting a more globular conformation. We also studied the energetics of the interaction using calorimetry and computational methods. All our data indicate that calmodulin binds to the peptide from cx43 in the classical ‘collapsed’ conformation.