Plant growth and respiration re-visited: maintenance respiration defined - it is an emergent property of, not a separate process within, the system - and why the respiration : photosynthesis ratio is conservative

Background and Aims

Plant growth and respiration still has unresolved issues, examined here using a model. The aims of this work are to compare the model''s predictions with McCree''s observation-based respiration equation which led to the ‘growth respiration/maintenance respiration paradigm’ (GMRP) – this is required to give the model credibility; to clarify the nature of maintenance respiration (MR) using a model which does not represent MR explicitly; and to examine algebraic and numerical predictions for the respiration:photosynthesis ratio.

Methods

A two-state variable growth model is constructed, with structure and substrate, applicable on plant to ecosystem scales. Four processes are represented: photosynthesis, growth with growth respiration (GR), senescence giving a flux towards litter, and a recycling of some of this flux. There are four significant parameters: growth efficiency, rate constants for substrate utilization and structure senescence, and fraction of structure returned to the substrate pool.

Key Results

The model can simulate McCree''s data on respiration, providing an alternative interpretation to the GMRP. The model''s parameters are related to parameters used in this paradigm. MR is defined and calculated in terms of the model''s parameters in two ways: first during exponential growth at zero growth rate; and secondly at equilibrium. The approaches concur. The equilibrium respiration:photosynthesis ratio has the value of 0·4, depending only on growth efficiency and recycling fraction.

Conclusions

McCree''s equation is an approximation that the model can describe; it is mistaken to interpret his second coefficient as a maintenance requirement. An MR rate is defined and extracted algebraically from the model. MR as a specific process is not required and may be replaced with an approach from which an MR rate emerges. The model suggests that the respiration:photosynthesis ratio is conservative because it depends on two parameters only whose values are likely to be similar across ecosystems.     

Solution-based targeted genomic enrichment for precious DNA samples

ABSTRACT: BACKGROUND: Solution-based targeted genomic enrichment (TGE) protocols permit selective sequencing of genomic regions of interest on a massively parallel scale. These protocols could be improved by: 1) modifying or eliminating time consuming steps; 2) increasing yield to reduce input DNA and excessive PCR cycling; and 3) enhancing reproducible. RESULTS: We developed a solution-based TGE method for downstream Illumina sequencing in a non-automated workflow, adding standard Illumina barcode indexes during the post-hybridization amplification to allow for sample pooling prior to sequencing. The method utilizes Agilent SureSelect baits, primers and hybridization reagents for the capture, off-the-shelf reagents for the library preparation steps, and adaptor oligonucleotides for Illumina paired-end sequencing purchased directly from an oligonucleotide manufacturing company. CONCLUSIONS: This solution-based TGE method for Illumina sequencing is optimized for small- or medium-sized laboratories and addresses the weaknesses of standard protocols by reducing the amount of input DNA required, increasing capture yield, optimizing efficiency, and improving reproducibility.     

Protein kinase C signaling during T cell activation induces the endoplasmic reticulum stress response

T cell receptor (TCR) ligation (signal one) in the presence of co-stimulation (signal two) results in downstream signals that increase protein production enabling naïve T cells to fully activate and gain effector function. Enhanced production of proteins by a cell requires an increase in endoplasmic reticulum (ER) chaperone expression, which is accomplished through activation of a cellular mechanism known as the ER stress response. The ER stress response is initiated during the cascade of events that occur for the activation of many cells; however, this process has not been comprehensively studied for T cell function. In this study, we used primary T cells and mice circulating TCR transgenic CD8⁺ T cells to investigate ER chaperone expression in which TCR signaling was initiated in the presence or absence of co-stimulation. In the presence of both signals, in vitro and in vivo analyses demonstrated induction of the ER stress response, as evidenced by elevated expression of GRP78 and other ER chaperones. Unexpectedly, ER chaperones were also increased in T cells exposed only to signal one, a treatment known to cause T cells to enter the ‘nonresponsive’ states of anergy and tolerance. Treatment of T cells with an inhibitor to protein kinase C (PKC), a serine/threonine protein kinase found downstream of TCR signaling, indicated PKC is involved in the induction of the ER stress response during the T cell activation process, thus revealing a previously unknown role for this signaling protein in T cells. Collectively, these data suggest that induction of the ER stress response through PKC signaling is an important component for the preparation of a T cell response to antigen.     

Hepatitis B in a high prevalence New Zealand population: a mathematical model applied to infection control policy

Background

Chronic hepatitis B (CHB) is a vaccine preventable disease of global public health importance. The prevalence of CHB in New Zealand's Tongan population is over 10%, a level consistent with endemic infection, which contrasts to the low overall New Zealand prevalence (<0.5%). Despite the introduction of infant vaccination in 1988, coverage among Tongan children is estimated to be only 53%.

Aims

To estimate the population benefit of additional public health control measures besides ‘business as usual’ infant vaccination for hepatitis B in high prevalence populations.

Methods

A mathematical model of hepatitis B virus (HBV) transmission was used to predict future CHB prevalence in the New Zealand Tongan population under different infection control strategies.

Results

Prevalence of CHB is predicted to plateau at 2% in the New Zealand Tongan population if coverage remains at current levels, which are therefore insufficient to achieve long-term elimination of HBV. The critical proportion of immunisation coverage for elimination of the virus is estimated to be 73%. The effect of screening for HBV carriage and early disease management was unable to be quantified, but is likely to reduce the population burden of HBV infection and thus contribute to accelerating elimination.

Conclusions and recommendations

Mathematical models are a useful tool to forecast the future burden of CHB under a range of control strategy scenarios in high prevalence populations. Serosurveillance and targeted vaccination has similarly arrested HBV transmission in time-series prevalence studies from Taiwan and Alaska. Such a policy may demonstrate similar efficacy in New Zealand ethnic groups with endemic HBV infection.     

Dynamics of Fructan and Sucrose Biosynthesis in Crested Wheatgrass

Fructan metabolism occurs in many temperate grasses when ambienttemperatures are cool. Fructan is believed to influence thecold hardiness of grasses and to have osmoregulatory and carbohydratestorage functions. In the cold deserts of the western UnitedStates, crested wheatgrass (Agropyron spp.) usually maintainsmetabolically active leaves throughout the winter. The investigationreported here concerns nonstructural carbohydrate content ofcrested wheatgrass during a growing season (September-June).Fructan accumulated in plant parts during the fall and springwhen temperatures were near 15?C. However, fructan content waslowest when temperatures were coldest. Surose content peakedwhen fructan levels were low and when maximum daily temperaturesremained below 0?C. We propose that fructan biosynthesis inleaf vacuoles provides a sink for photosynthates when temperaturesare too cold for translocation, and growth. Stored fructan thenprovide a readily available substrate for sucrose synthesisand plant growth. Because crested wheatgrass maintains greenleaves during the winter and is capable of photosynthesis attemperatures near 0?C, less stored carbohydrates are requiredfor respiratory maintenance and spring growth than for warm-seasongrasses. ¹Cooperative investigations of the USDA-Agricultural ResearchService and the Utah Agricultural Experiment Station, Logan,Utah 84322, U.S.A. Approved as Journal Paper No. 3755. ²Plant Physiologists, USDA-ARS-Forage and Range Research, Logan,UT 84322-6300, U.S.A. (Received March 25, 1988; Accepted July 11, 1988)     

Poor physical fitness is independently associated with mild cognitive impairment in elderly Koreans

The purpose of this study was to investigate the association between physical fitness and mild cognitive impairment (MCI) in elderly Koreans. This was a cross-sectional study that involved 134 men and 299 women aged 65 to 88 years. Six senior fitness tests were used as independent variables: 30 s chair stand for lower body strength, arm curl for upper body strength, chair-sit-and-reach for lower body flexibility, back scratch for upper body flexibility, 8-ft up-and-go for agility/dynamic balance, and 2-min walk for aerobic endurance. Global cognitive function was assessed using the Korean version of the Mini-Mental State Examination (MMSE). Potential covariates such as age, education levels, blood lipids, and insulin resistance (IR) markers were also assessed. Compared to individuals without MMSE-based MCI, individuals with MMSE-based MCI had poor physical fitness based on the senior fitness test (SFT). There were significant positive trends observed for education level (p=0.001) and MMSE score (p<0.001) across incremental levels of physical fitness in this study population. Individuals with moderate (OR=0.341, p=0.006) and high (OR=0.271, p=0.007) physical fitness based on a composite score of the SFT measures were less likely to have MMSE-based MCI than individuals with low physical fitness (referent, OR=1). The strength of the association between moderate (OR=0.377, p=0.038) or high (OR=0.282, p=0.050) physical fitness and MMSE-based MCI was somewhat attenuated but remained statistically significant even after adjustment for the measured compounding factors. We found that poor physical fitness was independently associated with MMSE-based MCI in elderly Koreans.