Interspecific differences in aluminium tolerance in relation to root cation-exchange capacity

Genotypic differences in aluminium (Al) tolerance hold considerable promise in overcoming an important limitation to plant growth in acid soils. Little is known, however, about the biochemical basis of such differences. Extracellular properties, particularly low root cation-exchange capacity (CEC), have been associated with Al tolerance, since roots of low CEC adsorb less Al than do those of high CEC. A solution culture study was conducted in which 12 plant species (monocots and dicots) were grown in solution culture of low ionic strength (ca 2 mM) for 8 d at four Al concentrations (0, 16, 28 and 55 M). The species differed significantly in Al tolerance as shown by differences in root length. Root length relative to that of the same species grown in the absence of Al varied from 6 to 117% at 16 M Al, and from 6 to 75% at 28 M Al. Species tolerance of Al was not closely associated with differences in root CEC. Although in some species Al sensitivity was associated with high adsorption of Al during a 10- or 40-min exposure to Al (expressed on a fresh mass or root length basis), this was not a good predictor of Al tolerance across all species studied.     

13C, 2H NMR Studies of Structural and Dynamical Modifications of Glucose-Exposed Porcine Aortic Elastin

Elastin, the principal component of the elastic fiber of the extracellular matrix, imparts to vertebrate tissues remarkable resilience and longevity. This work focuses on elucidating dynamical and structural modifications of porcine aortic elastin exposed to glucose by solid-state NMR spectroscopic and relaxation methodologies. Results from macroscopic stress-strain tests are also presented and indicate that glucose-treated elastin is mechanically stiffer than the same tissue without glucose treatment. These measurements show a large hysteresis in the stress-strain behavior of glucose-treated elastin—a well-known signature of viscoelasticity. Two-dimensional relaxation NMR methods were used to investigate the correlation time, distribution, and population of water in these samples. Differences are observed between the relative populations of water, whereas the measured correlation times of tumbling motion of water across the samples were similar. ¹³C magic-angle-spinning NMR methods were applied to investigate structural and dynamical modifications after glucose treatment. Although some overall structure is preserved, the process of glucose exposure results in more heterogeneous structures and slower mobility. The correlation times of tumbling motion of the ¹³C-¹H internuclear vectors in the glucose-treated sample are larger than in untreated samples, pointing to their more rigid structure. The ¹³C cross-polarization spectra reveal a notably increased α-helical character in the alanine motifs after glucose exposure. Results from molecular dynamics simulations are provided that add further insight into dynamical and structural changes of a short repeat, [VPGVG]₅, an alanine pentamer, desmosine, and isodesmosine sites with and without glucose. The simulations point to changes in the entropic and energetic contributions in the retractive forces of VPGVG and AAAAA motifs. The most notable change is the increase of the energetic contribution in the retractive force due to peptide-glucose interactions of the VPGVG motif, which may play an important role in the observed stiffening in glucose-treated elastin.     

The effect of prymnesin on the electric conductivity of thin lipid membranes

Summary A proteolipidic toxin, prymnesin, when added to the aqueous solutions around thin lipid membranes causes a marked increase in membrane conductance. The toxin-treated membrane is cation-permselective. The extent of cation permselectivity is dependent upon ionic strength of the aqueous solutions in a fashion similar to the dependence of cation permselectivity of a cation exchanger containing about 100mm of fixed negative sites. Dose-response relationship studies reveal a linear relation between log prymnesin concentration and log membrane conductance. The slope of the curve is around 3 if the toxin is applied to one side of the membrane and is around 7 if the toxin is applied to both sides of the membrane. The membrane treated with toxin on one side only is clearly asymmetric in its properties. These characteristics are expressed by an asymmetric current-voltage relationship, and by asymmetric sensitivity of membrane conductance to pH and to salt concentration. The conductance of the toxin-treated membrane is inversely proportional to temperature. It is suggested that aggregates of toxin moieties assemble in the membrane to form negatively charged aqueous pores. There is roughly a good correlation between the increase in membrane conductance and the increase in membrane permeability to urea if both were attributed to the formation of aqueous channels in the membrane.     

The interaction of phagocytes and the large-sized parasite Cryptococcus neoformans: Cytochemical and ultrastructural study

Summary The yeast Cryptococcus neoformans may develop under certain conditions a large polysaccharide capsule 50–100 M in diameter and therefore cannot be phagocytosed by either polymorphonuclear cells (PMN's) or mononuclear phagocytes (MN's). The cellular defense mechanism — in various animals — against the yeast is composed by formation of ringlike structure of PMN's or MN's cells which surround the C. neoformans. Ring structures develop either in vivo or in vitro in tissue culture; destruction of the yeast occurs within 36–72 hours.Several hydrolases, such as acid phosphatase, -glucuronidase and non-specific esterase were found to be released from the phagocytic cells into the enclosed yeast. Considerable reduction of NBT used as a marker for oxidative activity was observed in MN rings at contact regions of the MN cells and the yeast. Electron microscopic studies indicate that the phagocytic cells in the ring structure have many pseudopodes penetrating into the polysaccharide capsule of the yeast. Disintegration of the capsule was observed as well as phagocytosis of its material. A possible analogy between normal phagocytosis of small-sized bodies and the ring structure obtained when large bodies are involved is discussed.     

Effect of trabecular curvature on the stiffness of trabecular bone

Simplified structural models of trabecular bone have been used to model various forms of trabecular variability. The structural effects of variability of direction, length and thickness of the trabeculae have been studied using 'lattice-type' finite element models. However, many of the trabeculae are not perfectly straight, and have a small degree of curvature. The objective of this study is to quantify the influence of small curvatures of the trabeculae on the effective modulus of trabecular bone, in the principal material direction. An analytical analysis of the effect of curvature on a single trabecula is performed, utilizing the concept of cellular-solid models. Closed-form expressions are derived for the effect of curvature on the flexibility in the principal material direction. For comparison, expressions are derived for the flexibility of a straight oblique element, representing angular variability. A quantitative comparison is presented, which is dependent on the thickness of the trabeculae. It was found that small curvatures have a large effect on the stiffness of the trabecular structure. This effect is largest for thin trabeculae, and decreases for thick trabeculae. The stiffness of the trabecular structure can be reduced by a factor of up to four for thin trabeculae and up to two for thick trabeculae, even for small curvatures. The flexibility of curved elements is found to be larger than the flexibility of oblique elements with similar eccentricities. Thus it seems that curvature might play a role in determining the effective modulus of trabecular bone.     

Endpiece: Ideas must be comforting

ObjectivesTo explore general practitioners’ perceptions of effective health care and its application in their own practice; to examine how these perceptions relate to assumptions about clinicians’ values and behaviour implicit in the evidence based medicine approach.DesignA qualitative study using semistructured interviews.SettingEight general practices in North Thames region that were part of the Medical Research Council General Practice Research Framework.Participants24 general practitioners, three from each practice.ResultsThree categories of definitions emerged: clinical, patient related, and resource related. Patient factors were the main reason given for not practising effectively; others were lack of time, doctors’ lack of knowledge and skills, lack of resources, and “human failings.” Main sources of information used in situations of clinical uncertainty were general practitioner partners and hospital doctors. Contact with hospital doctors and observation of hospital practice were just as likely as information from medical and scientific literature to bring about changes in clinical practice.ConclusionsThe findings suggest that the central assumptions of the evidence based medicine paradigm may not be shared by many general practitioners, making its application in general practice problematic. The promotion of effective care in general practice requires a broader vision and a more pragmatic approach which takes account of practitioners’ concerns and is compatible with the complex nature of their work.

Key messages

• Evidence based medicine has emerged as a new paradigm to prevent inappropriate variations in clinical practice
• This study explored the extent to which evidence based medicine’s emphasis on clinical effectiveness, self analysis, and information seeking is congruent with the modes of thinking and behaviour of general practitioners
• General practitioners’ definitions of effective health care fell into three categories of clinical, patient related, and resource related; their main reason for not practising effectively was patient factors, and others were lack of time, lack of knowledge and skills, lack of resources, and “human failings”; and their main sources of information in cases of clinical uncertainty were general practitioner partners and hospital doctors
• The central assumptions of the evidence based medicine paradigm may not be shared by many general practitioners, making its application in general practice problematic
• Promotion of effective care in general practice requires a broader vision and a more pragmatic approach that takes account of practitioners’ concerns and is compatible with the complex nature of their work

     

Induction of oestrus and ovulation in anoestrous fallow deer (Dama dama) by using progesterone and GnRH treatment

Fourteen seasonally anoestrous, non-lactating fallow does were each treated with an intravaginal progesterone device for 14 days followed by a subcutaneously implanted osmotic minipump delivering synthetic GnRH at doses of 125 ng/h (7 does) or 250 ng/h (7 does) for up to 7 days, about 6 weeks before the natural breeding season. One doe (low delivery rate) lost its intravaginal device and 6 of the remaining does (46.2%) exhibited oestrus between 71 and 120 h after progesterone withdrawal/minipump insertion. Only one of these does received the low GnRH delivery rate and 5 received the high rate. Serum progesterone profiles indicated that an induced oestrus was followed by apparently normal luteal development. Does which did not exhibit oestrus failed to show a luteal response. Only 1 doe conceived at induced oestrus, producing a viable female fawn 6 weeks before the start of the natural fawning season. The remaining does returned to an anoestrous state until the onset of the natural breeding season.     

Diverse subcellular locations of cryptogein-induced reactive oxygen species production in tobacco Bright Yellow-2 cells

Reactive oxygen species (ROS) play a crucial role in many cellular responses and signaling pathways, including the oxidative burst defense response to pathogens. We have examined very early events in cryptogein-induced ROS production in tobacco (Nicotiana tabacum) Bright Yellow-2 suspension cells. Using Amplex Red and Amplex Ultra Red reagents, which report real-time H2O2 accumulation in cell populations, we show that the internal signal for H2O2 develops more rapidly than the external apoplastic signal. Subcellular accumulation of H2O2 was also followed in individual cells using the 2',7'-dichlorofluorescein diacetate fluorescent probe. Major accumulation was detected in endomembrane, cytoplasmic, and nuclear compartments. When cryptogein was added, the signal developed first in the nuclear region and, after a short delay, in the cell periphery. Interestingly, isolated nuclei were capable of producing H2O2 in a calcium-dependent manner, implying that nuclei can serve as a potential active source of ROS production. These results show complex spatial compartmentalization for ROS accumulation and an unexpected temporal sequence of events that occurs after cryptogein application, suggesting novel intricacy in ROS-signaling cascades.