Sensitivity of respiratory metabolism and efficiency to foliar nitrogen during growth and maintenance

Scaling of respiration from the leaf to the canopy level currently depends on identification of physiological parameters that are tightly linked to respiration and that can readily be determined. Several recent studies have helped provide guides to predicting whole canopy respiration on the basis of foliar nitrogen (N). This approach is potentially powerful owing to the well‐described patterns of allocation of N that follow interception of radiation. In the present study, we investigated the sensitivity of the N–respiration correlation to environmental and developmental factors, in order to evaluate its usage for attempts to scale respiration to the organism and ecosystem level. We studied fully expanded, 1 and 2‐year‐old, and current‐year needles from canopies of Pinus radiata that had been treated (unthinned, thinned and thinned+fertilized treatments) in ways likely to induce a wide range of growth and respiratory responses. We examined respiration in detail during the growth period in spring and again at the end of summer, using calorespirometric methods (combined measurements of CO₂ and heat rates) to determine the respiration rates , instantaneous enthalpic growth rates (R_SGΔH_B, a measure of the conservation of electrons in anabolic products) and the enthalpy conversion efficiency (η_H) of needles differing in age. A general linear model revealed that was positively correlated with needle N, but this correlation was strongly dependent on the season and the needle age – indicating an important physiological difference between expanding young needles and fully expanded old needles. Furthermore, the strength of the correlation between needle N and respiration was comparatively weak for the current year, expanding foliage, indicating that factors other than foliage N significantly influenced the respiration of young needles. The analysis of instantaneous growth rates revealed two general processes. Older, nonexpanding foliage showed considerable rates of enthalpic growth (increases in enthalpy) that was mainly caused by the increment of lignin during secondary growth. Secondly, canopy development appeared dynamic and to be optimized according to environmental drivers and constraints – such as light and water availability. In late spring, needle extension slowed in the upper, but not the lower canopy, because the upper canopy appeared to be affected first by the onset of drought stress in late spring. Growth rates were reduced in the upper canopy despite greater rates of respiration, indicating higher demand of ATP for the maintenance of protein and for export of sugars. Consequently, the enthalpy conversion efficiency and enthalpic N productivity (enthalpic growth per unit N) were comparatively poor indicating advanced development of needles in the upper canopy. We suggest that the growth and maintenance paradigm of respiration is, at best, only moderately useful when applied to whole trees, and is not valid at the cellular level or that of the plant organ. A different concept, namely that of respiratory efficiency, seems a more suitable way to represent respiration in carbon (C) balance models and should help provide a better mechanistic understanding of how respiration affects the C conversion efficiency of plants, and ultimately the net primary productivity of ecosystems.     

Rotavirus Architecture at Subnanometer Resolution

Rotavirus, a nonturreted member of the Reoviridae, is the causative agent of severe infantile diarrhea. The double-stranded RNA genome encodes six structural proteins that make up the triple-layer particle. X-ray crystallography has elucidated the structure of one of these capsid proteins, VP6, and two domains from VP4, the spike protein. Complementing this work, electron cryomicroscopy (cryoEM) has provided relatively low-resolution structures for the triple-layer capsid in several biochemical states. However, a complete, high-resolution structural model of rotavirus remains unresolved. Combining new structural analysis techniques with the subnanometer-resolution cryoEM structure of rotavirus, we now provide a more detailed structural model for the major capsid proteins and their interactions within the triple-layer particle. Through a series of intersubunit interactions, the spike protein (VP4) adopts a dimeric appearance above the capsid surface, while forming a trimeric base anchored inside one of the three types of aqueous channels between VP7 and VP6 capsid layers. While the trimeric base suggests the presence of three VP4 molecules in one spike, only hints of the third molecule are observed above the capsid surface. Beyond their interactions with VP4, the interactions between VP6 and VP7 subunits could also be readily identified. In the innermost T=1 layer composed of VP2, visualization of the secondary structure elements allowed us to identify the polypeptide fold for VP2 and examine the complex network of interactions between this layer and the T=13 VP6 layer. This integrated structural approach has resulted in a relatively high-resolution structural model for the complete, infectious structure of rotavirus, as well as revealing the subtle nuances required for maintaining interactions in such a large macromolecular assembly.     

The Impact of Antiretroviral Therapy in a Cohort of HIV Infected Patients Going in and out of the San Francisco County Jail

Background

Jails are an important venue of HIV care and a place for identification, treatment and referral for care. HIV infected inmates in the San Francisco County jail are offered antiretroviral treatment (ART), which many take only while in jail. We evaluated the effect of ART administration in a cohort of jail inmates going in and out of jail over a nine year period.

Methodology/Principal Findings

In this retrospective study, we examined inmates with HIV going in and out of jail. Inmates were categorized by patterns of ART use: continuous ART - ART both in and out of jail, intermittent ART - ART only in jail; never on ART - eligible by national guidelines, but refused ART. CD4 and HIV viral load (VL) were compared over time in these groups. Over a 9 year period, 512 inmates were studied: 388 (76%) on intermittent ART, 79 (15%) on continuous ART and 45(9%) never-on ART. In a linear mixed model analysis, inmates on intermittent ART were 1.43; 95%CI (1.03, 1.99) times and those never on ART were 2.89; 95%CI (1.71, 4.87) times more likely to have higher VL than inmates on continuous ART. Furthermore, Inmates on intermittent ART and never-on ART lost 1.60; 95%CI (1.06, 2.13) and 1.97; 95%CI (0.96, 3.00) more CD4 cells per month, respectively, compared to continuously treated inmates. The continuous ART inmates gained 0.67CD4 cells/month.

Conclusions/Significance

Continuous ART therapy in jail inmate''s benefits CD4 cell counts and control of VL especially compared to those who never took ART. Although jail inmates on intermittent ART were more likely to lose CD4 cells and experience higher VL over time than those on continuous ART, CD4 cell loss was slower in these inmates as compared to inmates never on ART. Further studies are needed to evaluate whether or not intermittent ART provides some benefit in outcome if continuous ART is not possible or likely.     

Norovirus disease: changing epidemiology and host susceptibility factors

Noroviruses cause the majority of acute viral gastroenteritis cases that occur worldwide. The increased recognition of noroviruses as the cause of outbreaks and sporadic disease is due to the recent availability of improved norovirus-specific diagnostics. Transmission of these viruses is facilitated by their high prevalence in the community, shedding of infectious virus particles from asymptomatic individuals and the high stability of the virus in the environment. Currently, the spectrum of clinical disease and the understanding of host susceptibility factors are changing. Cases of chronic norovirus gastroenteritis have been observed in transplant recipients and unusual clinical presentations have been recognized in otherwise healthy adults that are under physical stress. Recently, noroviruses were found to bind to gut-expressed carbohydrates, leading to a correlation between a person's genetically determined carbohydrate expression and their susceptibility to Norwalk virus infection. Greater community surveillance and further investigation of carbohydrate receptor-binding properties could provide further insights into norovirus transmission, susceptibility and pathogenesis, and should aid in developing vaccines and antiviral therapies for this common viral disease.     

Interactions between rotavirus and gastrointestinal cells

Rotaviruses are the leading cause of life-threatening diarrheal disease in infants and in young animals worldwide. The outcome of rotavirus infection of intestinal epithelial cells is more complex and involves induction of more diverse cellular responses than initially appreciated. Similar to bacteria, the pathogenesis of rotavirus-induced disease involves an enterotoxin, activation of the enteric nervous system and malabsorption, suggesting that common mechanisms of pathogenesis may exist between viral and bacterial pathogens.     

Maintenance of Y receptor dimers in epithelial cells depends on interaction with G-protein heterotrimers

Treatment of CHO cells expressing human Y receptors (Y₁, Y₂ or Y4 subtype) with pertussis toxin results in a large decrease in functional receptors, with a preferential loss of heteropentameric assemblies of receptor dimers and G-protein trimers. This occurs in parallel to inactivation of the nucleotide site of Gi α subunits, with a half period of about 4 h. The loss could be mainly due to proteolysis at the level of recycling/perinuclear endosomes, and of receptor completion in the ER, since it is reduced by co-treatment with ammonium chloride, an inhibitor of particulate proteinases. Antagonists do not strongly decrease the heteropentameric fraction. These findings indicate that the upkeep of Y receptor dimers in epithelial cell lines depends on the association of receptor oligomers with functional Gi α subunits. This interaction could use the juxtamembrane helix 8 in the fourth intracellular domain, and could also be supported by the C-terminal helix of the third intracellular loop, as outlined in the companion review (Parker et al., Amino Acids, doi:, 2010).