Osmoregulation and membrane-mediated responses to altered water potential in plant cells

Plant cells respond to short-term stress dehydration by modification of internal Ψ_π such that an inward gradient of Ψ_ω is maintained. In response to lowered Ψ_ω, increases in internal Ψ_π are created by alteration of cell inorganic ions and small organic solute content. Passive movement of water follows, changing cell hydration and forcing the plasma membrane against the elastic cell wall. The stretched cell wall presses against the cell contents, creating a hydrostatic pressure, Ψ_π, which tends to force water out of the cell. The resulting hydrostatic pressure eventually comes into equilibrium with forces bringing water into the cell, largely Ψ_π, and the net flow of water ceases.The mechanism for sensing cell Ψ_ω changes is unknown but the initial event must be physical, not biochemical. The method of translation of such physical events into biochemical actions is also unknown but the Zimmermann model provides a means of signal transduction and amplification, through the alteration of membrane parameters, which could account for the observed changes. As for animal cells, cell levels of Ca²⁺ are important for their regulation of membrane P_j in these responses but unlike osmoregulation in higher animals, the involvement of plant hormones in these responses have not been clearly established. However, the important role of plant cell limiting membranes in plant cell osmoregulation responses seems obvious.     

Venous Graft Surgery in Treatment of Coronary Heart Disease

Sixty-seven patients have had aortocoronary venous graft bypass surgery by one surgeon for the relief of symptoms of severe coronary heart disease, including eight emergency operations. The overall operative, hospital, and late mortality was low in patients with favourable myocardial function and no previous myocardial infarction. There was a 7% mortality in patients with a normal preoperative chest radiogram, 8% mortality when the left ventricular end-diastolic pressure was normal preoperatively, and a 5% mortality in patients who had normal left ventricular angiograms. The overall mortality in all elective operations for cardiac pain resistant to medical treatment was 15·8%. 89% of survivors improved; 67% are pain-free. Exercise tolerance in survivors is increased by 135%, atrial pacing results are improved by 10%. Left ventricular end-diastolic pressure is unchanged. Left ventricular function on angiography is improved. The improvement in left ventricular function assessed objectively correlates positively with vein-graft patency, as does freedom from angina pectoris.     

A Balanced Ratio of Proteins from Gene G and Frameshift-Extended Gene GT Is Required for Phage Lambda Tail Assembly

In bacteriophage λ, the overlapping open reading frames G and T are expressed by a programmed translational frameshift similar to that of the gag-pol genes of many retroviruses to produce the proteins gpG and gpGT. An analogous frameshift is widely conserved among other dsDNA tailed phages in their corresponding “G” and “GT” tail genes even in the absence of detectable sequence homology. The longer protein gpGT is known to be essential for tail assembly, but the requirement for the shorter gpG remained unclear because mutations in gene G affect both proteins. A plasmid system that can direct the efficient synthesis of tails was created and used to show that gpG and gpGT are both essential for correct tail assembly. Phage complementation assays under conditions where levels of plasmid-expressed gpG or gpGT could be altered independently revealed that the correct molar ratio of these two related proteins, normally determined by the efficiency of the frameshift, is also crucial for efficient assembly of functional tails. Finally, the physical connection between the G and T domains of gpGT, a consequence of the frameshift mechanism of protein expression, appears to be important for efficient tail assembly.     

Insights into the Excitonic States of Individual Chlorosomes from Chlorobaculum tepidum

Green-sulfur bacteria have evolved a unique light-harvesting apparatus, the chlorosome, by which it is perfectly adapted to thrive photosynthetically under extremely low light conditions. We have used single-particle, optical spectroscopy to study the structure-function relationship of chlorosomes each of which incorporates hundreds of thousands of self-assembled bacteriochlorophyll (BChl) molecules. The electronically excited states of these molecular assemblies are described as Frenkel excitons whose photophysical properties depend crucially on the mutual arrangement of the pigments. The signature of these Frenkel excitons and its relation to the supramolecular organization of the chlorosome becomes accessible by optical spectroscopy. Because subtle spectral features get obscured by ensemble averaging, we have studied individual chlorosomes from wild-type Chlorobaculum tepidum by polarization-resolved fluorescence-excitation spectroscopy. This approach minimizes the inherent sample heterogeneity and allows us to reveal properties of the exciton states without ensemble averaging. The results are compared with predictions from computer simulations of various models of the supramolecular organization of the BChl monomers. We find that the photophysical properties of individual chlorosomes from wild-type Chlorobaculum tepidum are consistent with a (multiwall) helical arrangement of syn-anti stacked BChl molecules in cylinders and/or spirals of different size.     

Divergence of mycorrhizal fungal communities in crop production systems

Mycorrhizal fungi are present in all arable soils and colonize nearly all crops and weed pests of crops. They may be involved as mutualists or pathogens of crops in well known but poorly understood phenomena such as crop rotation and green manure effects on soil productivity. Crop change effects on mycorrhizal fungal community parameters were evaluated in three field experiments. In Experiment 1, soybean (Glycine max (L.) Merr. cv. Douglas) was grown continuously or rotated with corn (Zea mays L.), milo (Sorghum bicolor (L.) Moench), or fescue (Festuca arundinacea Schreb cv. Johnstone) for two years, then soybean was grown on all plots. Continuous soybean plots were dominated byGigaspora spp., while rotated crops were dominated byGlomus spp. Differences in communities and community indices of continuous soybean and rotated plots were reduced after growing soybeans on rotated plots. In Experiment 2, a fescue sod was plowed and pearl millet (Pennisetum americanum Leeke) or crabgrass (Digitaria sanguinalis (L.) Scop.) grown. Both hosts resulted in great changes in populations of individual species, decreases in community dominance, and increases in community diversity and equitability. Crabgrass also resulted in reduced species richness. In Experiment 3, tobacco (Nicotiana tabacum L.) or fescue was planted on adjacent tracts of land with a long-term history of either fescue (30 yr) or sorghum-sudangrass (Sorghum bicolor (L.) Moench. ×S. sudanense (Piper) Staph.) (3 yr). The long-term cropping history had major effects on the mycorrhizal fungal communities which were related to the expression of mycorrhizal stunt disease of tobacco. Changes occurred in these communities in response to either current-season crop. These experiments suggest that crop rotation causes large changes in mycorrhizal fungal communities, that these changes may be involved in the rotation effect on soil productivity, and that design of cropping systems should take mycorrhizal fungal communities into consideration.     

Is Motor Learning Mediated by tDCS Intensity?

Although tDCS has been shown to improve motor learning, previous studies reported rather small effects. Since physiological effects of tDCS depend on intensity, the present study evaluated this parameter in order to enhance the effect of tDCS on skill acquisition. The effect of different stimulation intensities of anodal tDCS (atDCS) was investigated in a double blind, sham controlled crossover design. In each condition, thirteen healthy subjects were instructed to perform a unimanual motor (sequence) learning task. Our results showed (1) a significant increase in the slope of the learning curve and (2) a significant improvement in motor performance at retention for 1.5 mA atDCS as compared to sham tDCS. No significant differences were reported between 1 mA atDCS and sham tDCS; and between 1.5 mA atDCS and 1 mA atDCS.