Effects of elevated atmospheric CO2 concentrations, clipping regimen and differential day/night atmospheric warming on tissue nitrogen concentrations of a perennial pasture grass

Forecasting the effects of climate change on nitrogen (N) cycling in pastures requires an understanding of changes in tissue N. We examined the effects of elevated atmospheric CO2 concentration, atmospheric warming and simulated grazing (clipping frequency) on aboveground and belowground tissue N concentrations and C : N ratios of a C3 pasture grass. Phalaris aquatica L. cv. 'Holdfast' was grown in the field in six transparent temperature gradient tunnels (18 × 1.5 × 1.5 m each), three at ambient atmospheric CO2 and three at 759 p.p.m. CO2. Within each tunnel, there were three air temperature treatments: ambient control, +2.2/+4.0 °C above ambient day/night warming and +3.0 °C continuous warming. A frequent and an infrequent clipping treatment were applied to each warming × CO2 combination. Green leaf N concentrations were decreased by elevated CO2 and increased by more frequent clipping. Both warming treatments increased leaf N concentrations under ambient CO2 concentrations, but did not significantly alter leaf N concentrations under elevated CO2 concentrations. Nitrogen resorption from leaves was decreased under elevated CO2 conditions as well as by more frequent clipping. Fine root N concentrations decreased strongly with increasing soil depth and were further decreased at the 10-60 cm soil depths by elevated CO2 concentrations. The interaction between the CO2 and warming treatments showed that leaf N concentration was affected in a non-additive manner. Changes in leaf C : N ratios were driven by changes in N concentration. Overall, the effects of CO2, warming and clipping treatments on aboveground tissue N concentrations were much greater than on belowground tissue.

Temperature responses of photosynthesis and respiration in a sub-Antarctic megaherb from Heard Island

Understanding the response of sub-Antarctic plants to a warming climate requires an understanding of the relationship of carbon gain and loss to temperature. In a field study on Heard Island, we investigated the responses of photosynthesis and respiration of the sub-Antarctic megaherb Pringlea antiscorbutica R. Br. to temperature. This was done by instantaneously manipulating leaf temperature in a gas exchange cuvette on plants adapted to natural temperature variation along an altitudinal gradient. There was little altitudinal variation in the temperature response of photosynthesis. Photosynthesis was much less responsive to temperature than electron transport, suggesting that Rubisco activity was generally the rate-limiting process. The temperature response of leaf respiration rates was greater in cold-grown (high altitude) plants compared with warm-grown (low altitude) plants. This thermal acclimation would enable plants to maintain a positive carbon budget over a greater temperature range.

Short-term outcomes after perinatal hypoxic ischemic encephalopathy: a report from the Children's Hospitals Neonatal Consortium HIE focus group

OBJECTIVE

To characterize infants affected with perinatal hypoxic ischemic encephalopathy (HIE) who were referred to regional neonatal intensive care units (NICUs) and their related short-term outcomes.

STUDY DESIGN

This is a descriptive study evaluating the data collected prospectively in the Children's Hospital Neonatal Database, comprised of 27 regional NICUs within their associated children's hospitals. A consecutive sample of 945 referred infants born ⩾36 weeks' gestation with perinatal HIE in the first 3 days of life over approximately 3 years (2010-July 2013) were included. Maternal and infant characteristics are described. Short-term outcomes were evaluated including medical comorbidities, mortality and status of survivors at discharge.

RESULT

High relative frequencies of maternal predisposing conditions, cesarean and operative vaginal deliveries were observed. Low Apgar scores, profound metabolic acidosis, extensive resuscitation in the delivery room, clinical and electroencephalographic (EEG) seizures, abnormal EEG background and brain imaging directly correlated with the severity of HIE. Therapeutic hypothermia was provided to 85% of infants, 15% of whom were classified as having mild HIE. Electrographic seizures were observed in 26% of the infants. Rates of complications and morbidities were similar to those reported in prior clinical trials and overall mortality was 15%.

CONCLUSION

Within this large contemporary cohort of newborns with perinatal HIE, the application of therapeutic hypothermia and associated neurodiagnostic studies appear to have expanded relative to reported clinical trials. Although seizure incidence and mortality were lower compared with those reported in the trials, it is unclear whether this represented improved outcomes or therapeutic drift with the treatment of milder disease.

Temperature responses of mesophyll conductance differ greatly between species

The temperature responses of mesophyll conductance (gm ) were investigated for nine species using carbon isotope techniques combining tunable diode laser spectroscopy and gas exchange measurements. Species included the evergreen trees Eucalyptus pauciflora and Quercus engelmannii; the tropical evergreen tree Lophostemon confertus; as well as the herbaceous species Nicotiana tabacum, Oryza sativa, Triticum aestivum, Gossypium hirsutum, Glycine max and Arabidopsis thaliana. Responses varied from a two- to threefold increase in mesophyll conductance between 15 and 40 °C observed for N. tabacum, G. hirsutum, G. max and E. pauciflora to almost no change in L. confertus and T. aestivum. To account for the different temperature responses between species, we suggest that there must be variation in both the activation energy for membrane permeability and the effective pathlength for liquid phase diffusion. Stomatal conductance was relatively independent of increases in leaf temperature and concomitant increases in leaf to air vapour pressure difference. Two exceptions were Eucalyptus and Gossypium, where stomatal conductance increased with temperature up to 35 °C despite increasing leaf to air vapour pressure. For a given species, temperature responses of stomatal and mesophyll conductance were independent of one another.

Global variability in leaf respiration in relation to climate, plant functional types and leaf traits

Leaf dark respiration (Rdark ) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of Rdark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in Rdark . Area-based Rdark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8-28°C). By contrast, Rdark at a standard T (25°C, Rdark (25) ) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher Rdark (25) at a given photosynthetic capacity (Vcmax (25) ) or leaf nitrogen concentration ([N]) than species at warmer sites. Rdark (25) values at any given Vcmax (25) or [N] were higher in herbs than in woody plants. The results highlight variation in Rdark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of Rdark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs).

Drought increases heat tolerance of leaf respiration in Eucalyptus globulus saplings grown under both ambient and elevated atmospheric [CO2] and temperature

Climate change is resulting in increasing atmospheric [CO2], rising growth temperature (T), and greater frequency/severity of drought, with each factor having the potential to alter the respiratory metabolism of leaves. Here, the effects of elevated atmospheric [CO2], sustained warming, and drought on leaf dark respiration (R(dark)), and the short-term T response of R(dark) were examined in Eucalyptus globulus. Comparisons were made using seedlings grown under different [CO2], T, and drought treatments. Using high resolution T-response curves of R(dark) measured over the 15-65 °C range, it was found that elevated [CO2], elevated growth T, and drought had little effect on rates of R(dark) measured at T <35 °C and that there was no interactive effect of [CO2], growth T, and drought on T response of R(dark). However, drought increased R(dark) at high leaf T typical of heatwave events (35-45 °C), and increased the measuring T at which maximal rates of R(dark) occurred (Tmax) by 8 °C (from 52 °C in well-watered plants to 60 °C in drought-treated plants). Leaf starch and soluble sugars decreased under drought and elevated growth T, respectively, but no effect was found under elevated [CO2]. Elevated [CO2] increased the Q 10 of R(dark) (i.e. proportional rise in R(dark) per 10 °C) over the 15-35 °C range, while drought increased Q 10 values between 35 °C and 45 °C. Collectively, the study highlights the dynamic nature of the T dependence of R dark in plants experiencing future climate change scenarios, particularly with respect to drought and elevated [CO2].

The Children's Hospitals Neonatal Database: an overview of patient complexity, outcomes and variation in care

The Children's Hospitals Neonatal Consortium is a multicenter collaboration of leaders from 27 regional neonatal intensive care units (NICUs) who partnered with the Children's Hospital Association to develop the Children's Hospitals Neonatal Database (CHND), launched in 2010. The purpose of this report is to provide a first summary of the population of infants cared for in these NICUs, including representative diagnoses and short-term outcomes, as well as to characterize the participating NICUs and institutions. During the first 2 1/2 years of data collection, 40910 infants were eligible. Few were born inside these hospitals (2.8%) and the median gestational age at birth was 36 weeks. Surgical intervention (32%) was common; however, mortality (5.6%) was infrequent. Initial queries into diagnosis-specific inter-center variation in care practices and short-term outcomes, including length of stay, showed striking differences. The CHND provides a contemporary, national benchmark of short-term outcomes for infants with uncommon neonatal illnesses. These data will be valuable in counseling families and for conducting observational studies, clinical trials and collaborative quality improvement initiatives.

Predicting death or tracheostomy placement in infants with severe bronchopulmonary dysplasia

OBJECTIVE

To estimate the risk of death or tracheostomy placement (D/T) in infants with severe bronchopulmonary dysplasia (sBPD) born < 32 weeks' gestation referred to regional neonatal intensive care units.

STUDY DESIGN

We conducted a retrospective cohort study in infants born < 32 weeks' gestation with sBPD in 2010-2011, using the Children's Hospital Neonatal Database. sBPD was defined as the need for FiO2 ⩾ 0.3, nasal cannula support >2 l min(-1) or positive pressure at 36 weeks' post menstrual age. The primary outcome was D/T before discharge. Predictors associated with D/T in bivariable analyses (P < 0.2) were used to develop a multivariable logistic regression equation using 80% of the cohort. This equation was validated in the remaining 20% of infants.

RESULT

Of 793 eligible patients, the mean gestational age was 26 weeks' and the median age at referral was 6.4 weeks. D/T occurred in 20% of infants. Multivariable analysis showed that later gestational age at birth, later age at referral along with pulmonary management as the primary reason for referral, mechanical ventilation at the time of referral, clinically diagnosed pulmonary hypertension, systemic corticosteroids after referral and occurrence of a bloodstream infection after referral were each associated with D/T. The model performed well with validation (area under curve 0.86, goodness-of-fit χ(2), P = 0.66).

CONCLUSION

Seven clinical variables predicted D/T in this large, contemporary cohort with sBPD. These results can be used to inform clinicians who counsel families of affected infants and to assist in the design of future prospective trials.

Exploiting transplastomically modified Rubisco to rapidly measure natural diversity in its carbon isotope discrimination using tuneable diode laser spectroscopy

Carbon isotope discrimination (Δ) during C3 photosynthesis is dominated by the fractionation occurring during CO2-fixation by the enzyme Rubisco. While knowing the fractionation by enzymes is pivotal to fully understanding plant carbon metabolism, little is known about variation in the discrimination factor of Rubisco (b) as it is difficult to measure using existing in vitro methodologies. Tuneable diode laser absorption spectroscopy has improved the ability to make rapid measurements of Δ concurrently with photosynthetic gas exchange. This study used this technique to estimate b in vivo in five tobacco (Nicotiana tabacum L. cv Petit Havana [N,N]) genotypes expressing alternative Rubisco isoforms. For transplastomic tobacco producing Rhodospirillum rubrum Rubisco b was 23.8±0.7‰, while Rubisco containing the large subunit Leu-335-Val mutation had a b-value of 13.9±0.7‰. These values were significantly less than that for Rubisco from wild-type tobacco (b=29‰), a C3 species. Transplastomic tobacco producing chimeric Rubisco comprising tobacco Rubisco small subunits and the catalytic large subunits from either the C4 species Flaveria bidentis or the C3-C4 species Flaveria floridana had b-values of 27.8±0.8 and 28.6±0.6‰, respectively. These values were not significantly different from tobacco Rubisco.

Effects of fibroblast growth factor 9 on steroidogenesis and control of FGFR2IIIc mRNA in porcine granulosa cells

The objectives of this study were to investigate the effects of fibroblast growth factor 9 (FGF9) on hormone-stimulated porcine granulosa cell proliferation and steroid production and to further elucidate the hormonal and developmental control of FGFR2IIIc gene expression in granulosa cells. Porcine ovaries were collected from a local slaughterhouse and granulosa cells were collected from small to medium (1 to 5 mm) follicles for 5 in vitro studies that were conducted. Cells were cultured for 48 h in 5% fetal calf serum plus 5% porcine serum and then treated with various combinations of FSH, IGF-I, FGF9, Sonic hedgehog (SHH), cortisol, PGE2, and/or wingless-type mouse mammary tumor virus integration site family member 5A (WNT5A) in serum-free medium for an additional 24 or 48 h. Medium was collected for analysis of steroid concentration via RIA, or RNA was collected for gene expression analysis of FGFR2IIIc via quantitative reverse transcription PCR. Fibroblast growth factor 9 stimulated (P < 0.05) IGF-I-induced estradiol production in the presence of FSH and testosterone. However, FGF9 had inconsistent effects on progesterone production, stimulating progesterone production in the presence of FSH and testosterone but inhibiting progesterone production in the presence of IGF-I, FSH, and testosterone. Cell numbers were increased (P < 0.05) by FGF9 in the presence of IGF-I and FSH but not in the presence of FSH and absence of IGF-I. For FGFR2IIIc mRNA studies, granulosa cells were treated with FSH, IGF-I, FGF9, SHH, cortisol, PGE2, or WNT5A. Follicle-stimulating hormone alone had no effect (P > 0.10) whereas IGF-I increased (P < 0.05) FGFR2IIIc mRNA abundance. Cortisol, PGE2, SHH, and WNT5A had no effect (P > 0.10) on FGFR2IIIc gene expression whereas FGF9 in the presence of FSH and IGF-I inhibited (P < 0.05) FGFR2IIIc gene expression. In an in vivo study, granulosa cells from large (7 to 14 mm) follicles had greater (P < 0.05) abundance of FGFR2IIIc mRNA than small (1 to 3 mm) or medium (4 to 6 mm) follicles. In conclusion, IGF-I-induced FGFR2IIIc mRNA may be a mechanism for increased responses to FGF9 in FSH plus IGF-I-treated granulosa cells. Fibroblast growth factor 9 and IGF-I may work together as amplifiers of follicular growth and granulosa cell differentiation by stimulating estradiol production and concomitantly stimulating granulosa cell growth in pigs.

PrometheusWiki Gold Leaf Protocol: gas exchange using LI-COR 6400

This leaf gas exchange protocol enables light or CO2 response curves using a LI-COR LI-6400 portable photosynthesis system. The protocol originates in PrometheusWiki (http://prometheuswiki.publish.csiro.au/) where it has been tested and verified, and has received favourable user reviews. This reformatted and non-editable version is published as a Gold Leaf Protocol. For the most current version, including any user-commentary updates, readers may view the live version of the protocol at http://bit.ly/PWLicorGold.

Therapeutic interventions and short-term outcomes for infants with severe bronchopulmonary dysplasia born at <32 weeks' gestation

OBJECTIVE

To characterize the treatments and short-term outcomes in infants with severe bronchopulmonary dysplasia (sBPD) referred to regional neonatal intensive care units.

STUDY DESIGN

Infants born <32 weeks' gestation with sBPD were identified using the Children's Hospital Neonatal Database. Descriptive outcomes are reported.

RESULT

A total of 867 patients were eligible. On average, infants were born at 26 weeks' gestation and referred 43 days after birth. Infants frequently experienced lung injury (pneumonia: 24.1%; air leak: 9%) and received systemic corticosteroids (61%) and mechanical ventilation (median duration 37 days). Although 91% survived to discharge, the mean post-menstrual age was 47 weeks. Ongoing care such as supplemental oxygen (66%) and tracheostomy (5%) were frequently needed.

CONCLUSION

Referred infants with sBPD sustain multiple insults to lung function and development. Because affected infants have no proven, safe or efficacious therapy and endure an exceptional burden of care even after referral, urgent work is required to observe and improve their outcomes.

Improving photosynthesis

Photosynthesis is the basis of plant growth, and improving photosynthesis can contribute toward greater food security in the coming decades as world population increases. Multiple targets have been identified that could be manipulated to increase crop photosynthesis. The most important target is Rubisco because it catalyses both carboxylation and oxygenation reactions and the majority of responses of photosynthesis to light, CO₂, and temperature are reflected in its kinetic properties. Oxygenase activity can be reduced either by concentrating CO₂ around Rubisco or by modifying the kinetic properties of Rubisco. The C₄ photosynthetic pathway is a CO₂-concentrating mechanism that generally enables C₄ plants to achieve greater efficiency in their use of light, nitrogen, and water than C₃ plants. To capitalize on these advantages, attempts have been made to engineer the C₄ pathway into C₃ rice (Oryza sativa). A simpler approach is to transfer bicarbonate transporters from cyanobacteria into chloroplasts and prevent CO₂ leakage. Recent technological breakthroughs now allow higher plant Rubisco to be engineered and assembled successfully in planta. Novel amino acid sequences can be introduced that have been impossible to reach via normal evolution, potentially enlarging the range of kinetic properties and breaking free from the constraints associated with covariation that have been observed between certain kinetic parameters. Capturing the promise of improved photosynthesis in greater yield potential will require continued efforts to improve carbon allocation within the plant as well as to maintain grain quality and resistance to disease and lodging.

High-resolution temperature responses of leaf respiration in snow gum (Eucalyptus pauciflora) reveal high-temperature limits to respiratory function

We tested whether snow gum (Eucalyptus pauciflora) trees growing in thermally contrasting environments exhibit generalizable temperature (T) response functions of leaf respiration (R) and fluorescence (Fo). Measurements were made on pot-grown saplings and field-grown trees (growing between 1380 and 2110 m a.s.l.). Using a continuous, high-resolution protocol, we quantified T response curves of R and Fo--these data were used to identify an algorithm for modelling R-T curves at subcritical T's and establish variations in heat tolerance. For the latter, we quantified Tmax [T where R is maximal] and Tcrit [T where Fo rises rapidly]. Tmax ranged from 51 to 57 °C, varying with season (e.g. winter  summer). Tcrit ranged from 41 to 49 °C in summer and from 58 to 63 °C in winter. Thus, surprisingly, leaf energy metabolism was more heat-tolerant in trees experiencing ice-encasement in winter than warmer conditions in summer. A polynomial model fitted to log-transformed R data provided the best description of the T-sensitivity of R (between 10 and 45 °C); using these model fits, we found that the negative slope of the Q10 -T relationship was greater in winter than in summer. Collectively, our results (1) highlight high-T limits of energy metabolism in E. pauciflora and (2) provide a framework for improving representation of T-responses of leaf R in predictive models.

Temperature response of carbon isotope discrimination and mesophyll conductance in tobacco

The partial pressure of CO2 at the sites of carboxylation within chloroplasts depends on the conductance to CO2 diffusion from intercellular airspace to the sites of carboxylation, termed mesophyll conductance (gm ). We investigated the temperature response of gm in tobacco (Nicotiana tabacum) by combining gas exchange in high light, ambient CO2 in either 2 or 21% O2 with carbon isotope measurements using tuneable diode laser spectroscopy. The gm increased linearly with temperature in 2 or 21% O2 . In 21% O2 , isotope discrimination associated with gm decreased from 5.0 ± 0.2 to 1.8 ± 0.2‰ as temperature increased from 15 to 40 °C, but the photorespiratory contribution to the isotopic signal is significant. While the fractionation factor for photorespiration (f = 16.2 ± 0.7‰) was independent of temperature between 20 and 35 °C, discrimination associated with photorespiration increased from 1.1 ± 0.01 to 2.7 ± 0.02‰ from 15 to 40 °C. Other mitochondrial respiration contributed around 0.2 ± 0.03‰. The drawdown in CO2 partial pressure from ambient air to intercellular airspaces was nearly independent of leaf temperature. By contrast, the increase in gm with increasing leaf temperature resulted in the drawdown in CO2 partial pressure between intercellular airspaces and the sites of carboxylation decreasing substantially at high temperature.

The cyanobacterial CCM as a source of genes for improving photosynthetic CO2 fixation in crop species

Crop yields need to nearly double over the next 35 years to keep pace with projected population growth. Improving photosynthesis, via a range of genetic engineering strategies, has been identified as a promising target for crop improvement with regard to increased photosynthetic yield and better water-use efficiency (WUE). One approach is based on integrating components of the highly efficient CO(2)-concentrating mechanism (CCM) present in cyanobacteria (blue-green algae) into the chloroplasts of key C(3) crop plants, particularly wheat and rice. Four progressive phases towards engineering components of the cyanobacterial CCM into C(3) species can be envisaged. The first phase (1a), and simplest, is to consider the transplantation of cyanobacterial bicarbonate transporters to C(3) chloroplasts, by host genomic expression and chloroplast targeting, to raise CO(2) levels in the chloroplast and provide a significant improvement in photosynthetic performance. Mathematical modelling indicates that improvements in photosynthesis as high as 28% could be achieved by introducing both of the single-gene, cyanobacterial bicarbonate transporters, known as BicA and SbtA, into C(3) plant chloroplasts. Part of the first phase (1b) includes the more challenging integration of a functional cyanobacterial carboxysome into the chloroplast by chloroplast genome transformation. The later three phases would be progressively more elaborate, taking longer to engineer other functional components of the cyanobacterial CCM into the chloroplast, and targeting photosynthetic and WUE efficiencies typical of C(4) photosynthesis. These later stages would include the addition of NDH-1-type CO(2) pumps and suppression of carbonic anhydrase and C(3) Rubisco in the chloroplast stroma. We include a score card for assessing the success of physiological modifications gained in phase 1a.

Antisense reductions in the PsbO protein of photosystem II leads to decreased quantum yield but similar maximal photosynthetic rates

Photosystem (PS) II is the multisubunit complex which uses light energy to split water, providing the reducing equivalents needed for photosynthesis. The complex is susceptible to damage from environmental stresses such as excess excitation energy and high temperature. This research investigated the in vivo photosynthetic consequences of impairments to PSII in Arabidopsis thaliana (ecotype Columbia) expressing an antisense construct to the PsbO proteins of PSII. Transgenic lines were obtained with between 25 and 60% of wild-type (WT) total PsbO protein content, with the PsbO1 isoform being more strongly reduced than PsbO2. These changes coincided with a decrease in functional PSII content. Low PsbO (less than 50% WT) plants grew more slowly and had lower chlorophyll content per leaf area. There was no change in content per unit area of cytochrome b6f, ATP synthase, or Rubisco, whereas PSI decreased in proportion to the reduction in chlorophyll content. The irradiance response of photosynthetic oxygen evolution showed that low PsbO plants had a reduced quantum yield, but matched the oxygen evolution rates of WT plants at saturating irradiance. It is suggested that these plants had a smaller pool of PSII centres, which are inefficiently connected to antenna pigments resulting in reduced photochemical efficiency.

Note: rotaphone, a new self-calibrated six-degree-of-freedom seismic sensor

We have developed and tested (calibration, linearity, and cross-axis errors) a new six-degree-of-freedom mechanical seismic sensor for collocated measurements of three translational and three rotational ground motion velocity components. The device consists of standard geophones arranged in parallel pairs to detect spatial gradients. The instrument operates in a high-frequency range (above the natural frequency of the geophones, 4.5 Hz). Its theoretical sensitivity limit in this range is 10(-9) m/s in ground velocity and 10(-9) rad/s in rotation rate. Small size and weight, and easy installation and maintenance make the instrument useful for local-earthquake recording and seismic prospecting.

Temperature response of mesophyll conductance in cultivated and wild Oryza species with contrasting mesophyll cell wall thickness

A critical component of photosynthetic capacity is the conductance of CO(2) from intercellular airspaces to the sites of CO(2) fixation in the stroma of chloroplasts, termed mesophyll conductance (g(m)). Leaf anatomy has been identified as an important determinant of g(m). There are few studies of the temperature response of g(m) and none has examined the implications of leaf anatomy. Hence, we compared a cultivar of Oryza sativa with two wild Oryza relatives endemic to the hot northern savannah of Australia, namely Oryza meridionalis and Oryza australiensis. All three species had similar leaf anatomical properties, except that the wild relatives had significantly thicker mesophyll cell walls than O. sativa. Thicker mesophyll cell walls in the wild rice species are likely to have contributed to the reduction in g(m) , which was associated with a greater drawdown of CO(2) into chloroplasts (C(i) -C(c) ) compared with O. sativa. Mesophyll conductance increased at higher temperatures, whereas the rate of CO(2) assimilation was relatively stable between 20 and 40 °C. Consequently, C(i) -C(c) decreased for all three species as temperature increased.

Functional analysis of corn husk photosynthesis

The husk surrounding the ear of corn/maize (Zea mays) has widely spaced veins with a number of interveinal mesophyll (M) cells and has been described as operating a partial C(3) photosynthetic pathway, in contrast to its leaves, which use the C(4) photosynthetic pathway. Here, we characterized photosynthesis in maize husk and leaf by measuring combined gas exchange and carbon isotope discrimination, the oxygen dependence of the CO(2) compensation point, and photosynthetic enzyme activity and localization together with anatomy. The CO(2) assimilation rate in the husk was less than that in the leaves and did not saturate at high CO(2), indicating CO(2) diffusion limitations. However, maximal photosynthetic rates were similar between the leaf and husk when expressed on a chlorophyll basis. The CO(2) compensation points of the husk were high compared with the leaf but did not vary with oxygen concentration. This and the low carbon isotope discrimination measured concurrently with gas exchange in the husk and leaf suggested C(4)-like photosynthesis in the husk. However, both Rubisco activity and the ratio of phosphoenolpyruvate carboxylase to Rubisco activity were reduced in the husk. Immunolocalization studies showed that phosphoenolpyruvate carboxylase is specifically localized in the layer of M cells surrounding the bundle sheath cells, while Rubisco and glycine decarboxylase were enriched in bundle sheath cells but also present in M cells. We conclude that maize husk operates C(4) photosynthesis dispersed around the widely spaced veins (analogous to leaves) in a diffusion-limited manner due to low M surface area exposed to intercellular air space, with the functional role of Rubisco and glycine decarboxylase in distant M yet to be explained.

An analysis of the natural course of compensatory sweating following thoracoscopic sympathectomy

BACKGROUND

To evaluate the long-term results of thoracoscopic sympathectomy in the treatment of hyperhydrosis.

METHODS

Theatre log books were used to identify all patients who underwent thoracoscopic sympathectomy between 2000 and 2006. Details of pre-operative symptoms, surgical procedure and post-operative complications were collected from the patient notes. Each patient was sent a questionnaire regarding success of the procedure, compensatory sweating and overall satisfaction.

RESULTS

46 hyperhydrosis patients (34 females) age range 14-57 years. 20 patients suffered with hyperhydrosis in a combination of areas, 14 in the axillae alone, 9 palms alone and with 2 facial symptoms. There were 2 early post-operative complications, 1 haemothorax which required a chest drain and a chest infection. 3 patients required redo procedures. Of follow-up of 42 months (range 6-84), 32 (69·5%) patients reported complete dryness or a significant improvement in symptoms and 15 a substantial improvement in quality of life. However 43 patients (93%) suffered with compensatory sweating, of these 27 had to change clothes more than once daily. Compensatory sweating was graded as severe in 18 and incapacitating in 2. Of note only 5 patients noticed an improvement in the compensatory sweating over time. Only 26 (56%) would recommend thoracoscopic sympathectomy to others with hyperhydrosis.

CONCLUSION

Thoracoscopic sympathectomy is effective in the treatment of hyperhydrosis. However compensatory sweating seems unavoidable and infrequently improves with time. Patients need to be carefully counselled before committing to surgery.