The role of Cytochrome b6f in the control of steady-state photosynthesis: a conceptual and quantitative model.

Here, we present a conceptual and quantitative model to describe the role of the Cytochrome [Formula: see text] complex in controlling steady-state electron transport in [Formula: see text] leaves. The model is based on new experimental methods to diagnose the maximum activity of Cyt [Formula: see text] in vivo, and to identify conditions under which photosynthetic control of Cyt [Formula: see text] is active or relaxed. With these approaches, we demonstrate that Cyt [Formula: see text] controls the trade-off between the speed and efficiency of electron transport under limiting light, and functions as a metabolic switch that transfers control to carbon metabolism under saturating light. We also present evidence that the onset of photosynthetic control of Cyt [Formula: see text] occurs within milliseconds of exposure to saturating light, much more quickly than the induction of non-photochemical quenching. We propose that photosynthetic control is the primary means of photoprotection and functions to manage excitation pressure, whereas non-photochemical quenching functions to manage excitation balance. We use these findings to extend the Farquhar et al. (Planta 149:78-90, 1980) model of [Formula: see text] photosynthesis to include a mechanistic description of the electron transport system. This framework relates the light captured by PS I and PS II to the energy and mass fluxes linking the photoacts with Cyt [Formula: see text], the ATP synthase, and Rubisco. It enables quantitative interpretation of pulse-amplitude modulated fluorometry and gas-exchange measurements, providing a new basis for analyzing how the electron transport system coordinates the supply of Fd, NADPH, and ATP with the dynamic demands of carbon metabolism, how efficient use of light is achieved under limiting light, and how photoprotection is achieved under saturating light. The model is designed to support forward as well as inverse applications. It can either be used in a stand-alone mode at the leaf-level or coupled to other models that resolve finer-scale or coarser-scale phenomena.

Large historical growth in global terrestrial gross primary production.

Growth in terrestrial gross primary production (GPP)-the amount of carbon dioxide that is 'fixed' into organic material through the photosynthesis of land plants-may provide a negative feedback for climate change. It remains uncertain, however, to what extent biogeochemical processes can suppress global GPP growth. As a consequence, modelling estimates of terrestrial carbon storage, and of feedbacks between the carbon cycle and climate, remain poorly constrained. Here we present a global, measurement-based estimate of GPP growth during the twentieth century that is based on long-term atmospheric carbonyl sulfide (COS) records, derived from ice-core, firn and ambient air samples. We interpret these records using a model that simulates changes in COS concentration according to changes in its sources and sinks-including a large sink that is related to GPP. We find that the observation-based COS record is most consistent with simulations of climate and the carbon cycle that assume large GPP growth during the twentieth century (31% ± 5% growth; mean ± 95% confidence interval). Although this COS analysis does not directly constrain models of future GPP growth, it does provide a global-scale benchmark for historical carbon-cycle simulations.

Improving respiration measurements with gas exchange analyzers.

Dark respiration measurements with open-flow gas exchange analyzers are often questioned for their low accuracy as their low values often reach the precision limit of the instrument. Respiration was measured in five species, two hypostomatous (Vitis Vinifera L. and Acanthus mollis) and three amphistomatous, one with similar amount of stomata in both sides (Eucalyptus citriodora) and two with different stomata density (Brassica oleracea and Vicia faba). CO2 differential (ΔCO2) increased two-fold with no change in apparent Rd, when the two leaves with higher stomatal density faced outside. These results showed a clear effect of the position of stomata on ΔCO2. Therefore, it can be concluded that leaf position is important to guarantee the improvement of respiration measurements increasing ΔCO2 without affecting the respiration results by leaf or mass units. This method will help to increase the accuracy of leaf respiration measurements using gas exchange analyzers.

Models of fluorescence and photosynthesis for interpreting measurements of solar-induced chlorophyll fluorescence.

We have extended a conventional photosynthesis model to simulate field and laboratory measurements of chlorophyll fluorescence at the leaf scale. The fluorescence paramaterization is based on a close nonlinear relationship between the relative light saturation of photosynthesis and nonradiative energy dissipation in plants of different species. This relationship diverged only among examined data sets under stressed (strongly light saturated) conditions, possibly caused by differences in xanthophyll pigment concentrations. The relationship was quantified after analyzing data sets of pulse amplitude modulated measurements of chlorophyll fluorescence and gas exchange of leaves of different species exposed to different levels of light, CO2, temperature, nitrogen fertilization treatments, and drought. We used this relationship in a photosynthesis model. The coupled model enabled us to quantify the relationships between steady state chlorophyll fluorescence yield, electron transport rate, and photosynthesis in leaves under different environmental conditions. KEY POINTS: Light saturation of photosynthesis determines quenching of leaf fluorescenceWe incorporated steady state leaf fluorescence in a photosynthesis model.

Photosynthetic control of atmospheric carbonyl sulfide during the growing season.

Climate models incorporate photosynthesis-climate feedbacks, yet we lack robust tools for large-scale assessments of these processes. Recent work suggests that carbonyl sulfide (COS), a trace gas consumed by plants, could provide a valuable constraint on photosynthesis. Here we analyze airborne observations of COS and carbon dioxide concentrations during the growing season over North America with a three-dimensional atmospheric transport model. We successfully modeled the persistent vertical drawdown of atmospheric COS using the quantitative relation between COS and photosynthesis that has been measured in plant chamber experiments. Furthermore, this drawdown is driven by plant uptake rather than other continental and oceanic fluxes in the model. These results provide quantitative evidence that COS gradients in the continental growing season may have broad use as a measurement-based photosynthesis tracer.

Phytochrome-driven changes in respiratory electron transport partitioning in soybean (Glycine max. L.) cotyledons.

After it was observed that light induces changes in electron partitioning between the cytochrome and the alternative pathway, the focus interest was directed to assessing what type of photoreceptors are involved and the extent of such modifications. Studies on 5-day-old soybean (Glycine max L.) cotyledons using an oxygen isotope fractionation technique showed that phytochrome is involved in changes in electron partitioning between the cytochrome and the alternative respiratory pathway. A follow-up of a previous study, showing that 5 min of white light caused changes in mitochondrial electron partitioning, demonstrated that while blue light was not involved in any such changes, red light caused a significant shift of electrons toward the alternative pathway. The major shift, observed after 24 h of light, is mainly due to both a decrease in the activity of the cytochrome pathway and an increase in the activity of the alternative pathway. The involvement of a phytochrome receptor was confirmed by demonstration of reversibility by far-red light. The implications of the possible involvement of phytochrome in the regulation of mitochondrial electron transport are discussed.

Analysis of leakage in IRGA's leaf chambers of open gas exchange systems: quantification and its effects in photosynthesis parameterization.

The measurement of the response of net photosynthesis to leaf internal CO2 (i.e. A-Ci curves) is widely used for ecophysiological studies. Most studies did not consider CO2 exchange between the chamber and the surrounding air, especially at the two extremes of A-Ci curves, where large CO2 gradients are created, leading to erroneous estimations of A and Ci. A quantitative analysis of CO2 leakage in the chamber of a portable open gas exchange system (Li-6400, LI-COR Inc., NE, USA) was performed. In an empty chamber, the measured CO2 leakage was similar to that calculated using the manufacturer's equations. However, in the presence of a photosynthetically inactive leaf, the magnitude of leakage was substantially decreased, although still significant. These results, together with the analysis of the effects of chamber size, tightness, flow rate, and gasket material, suggest that the leakage is larger at the interface between the gaskets than through the gaskets. This differential leakage rate affects the parameterization by photosynthesis models. The magnitude of these errors was assessed in tobacco plants. The results showed that leakage results in a 10% overestimation of the leaf maximum capacity for carboxylation (Vc,max) and a 40% overestimation of day respiration (Rl). Using the manufacturer's equations resulted in larger, non-realistic corrections of the true values. The photosynthetic response to CO2 concentrations at the chloroplast (i.e. A-Cc curves) was significantly less affected by leakage than A-Ci curves. Therefore, photosynthetic parameterization can be improved by: (i) correcting A and Ci values for chamber leakage estimated using a photosynthetically inactive leaf; and (ii) using A-Cc instead of A-Ci curves.

Nocturnal stomatal conductance effects on the delta(18)O signatures of foliage gas exchange observed in two forest ecosystems.

We report field observations of oxygen isotope ((18)O) discrimination during nocturnal foliage respiration ((18)Delta(R)) in branch chambers in two forest ecosystems: a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation in Scotland; and a beech (Fagus sylvatica L.) forest in Germany. We used observations and modeling to examine the impact of nocturnal stomatal conductance on the (18)O/(16)O (delta(18)O) signatures of foliage gas exchange at night. We found that nocturnal stomatal conductance can influence the delta(18)O signature by affecting: (1) the bidirectional diffusion of CO(2) into and out of the leaf (with isotopic equilibration); and (2) the (18)O enrichment of the foliage water with which the CO(2) equilibrates. Both effects were manifest in high apparent (18)Delta(R) values and enriched delta(18)O signatures of foliage water at night. The effects were more pronounced for Sitka spruce because of its higher nocturnal stomatal conductance and higher specific leaf water content compared to beech. We found that taking the effects of nocturnal stomatal conductance into account may change the sign of the delta(18)O signature of nocturnal foliage respiration, generally thought to decrease the delta(18)O of atmospheric CO(2). We conclude that nocturnal stomatal exchange can have a profound effect on isotopic exchange depending on species and environmental conditions. These effects can be important when using delta(18)O signatures of canopy CO(2) to distinguish foliage and soil respiration, and when modeling the delta(18)O signature of CO(2) exchanged between ecosystems and the atmosphere.

COX-2 involvement in breast cancer metastasis to bone.

Cyclooxygenase-2 (COX-2) is expressed in 40% of human invasive breast cancers. Bone is the predominant site of metastasis in case of breast cancer. We investigated the role of COX-2 in a suitable mouse model of breast cancer metastasis to bone using the whole-body luciferase imaging of cancer cells. We provide several lines of evidence that COX-2 produced in breast cancer cells is important for bone metastasis in this model including (1) COX-2 transfection enhanced the bone metastasis of MDA-435S cells and (2) breast cancer cells isolated and cultured from the bone metastases produced significantly more prostaglandin E(2) (an important mediator of COX-2) than the parental injected cell populations of breast cancer cells. Next, we found that a COX-2 inhibitor, MF-tricyclic, inhibited bone metastasis caused by a bone-seeking clone both in prevention regimen (in which case mice started receiving MF-tricyclic 1 week before the injection of cancer cells) and in treatment regimen (in which case mice received MF-tricyclic after the development of bone metastasis). These studies indicate that COX-2 produced in breast cancer cells may be vital to the development of osteolytic bone metastases in patients with breast cancer, and that COX-2 inhibitors may be useful in halting this process.

Non-steady state effects in diurnal 180 discrimination by Picea sitchensis branches in the field.

We report diurnal variations in 18O discrimination (18 delta) during photosynthesis (18 delta A) and respiration (18 delta R) of Picea sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18 delta (18 delta pred) based on concurrent measurements of branch gas exchange to evaluate steady state and non-steady state (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the Delta 18O of atmospheric CO2. The non-steady state approach substantially improved the agreement between 18 delta pred and observed 18 delta (18 delta obs) compared with the assumption of isotopic steady state (ISS) for the Delta 18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18 delta values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, neglecting these effects leads to an underestimation of daily net canopy isofluxes from this forest by up to 30%. We expect NSS effects to be most pronounced in species with high specific leaf water content such as conifers and when stomata are open at night or when there is high relative humidity, and we suggest modifications to ecosystem and global models of delta 18O of CO2.

Analysis of intracytoplasmic sperm injection procedures related to delayed insemination and ejaculated, epididymal and testicular spermatozoa.

In all, 1210 treatment cycles were divided into three categories for retrospective analysis according to the period of delay between oocyte retrieval (occurring at a fixed time after human chorionic gonadotrophin) and intracytoplasmic sperm injection (ICSI) of <3 h, 3-5 h, >5 h (referred to as 'delayed ICSI'). Three stages from oocyte to the birth of a live baby were identified for statistical analysis, (i) fertilization (2PN zygotes), (ii) cleavage of 2PN zygotes, (iii) transferred embryo to live birth. Stages 1, 2 and 3 were analysed statistically for the three time periods. Chi-square analysis showed no significant effect of delayed ICSI on fertilization (chi(2) = 3.615, P = 0.65), and embryo transfer to birth (chi(2) = 1.840, P = 0.399). The effect on cleavage was significant (chi(2) = 9.625, P = 0.008). However, shorter incubation times produced results which were better than the traditional longer ones. The success rate at the cleavage stage was so high that the marginal advantage had very little effect on the overall process. This study of a substantial patient sample establishes that ICSI on a peri-ovulatory oocyte (<3 h after oocyte retrieval) does not compromise outcome parameters, and that longer periods of incubation (>5 h) do not offer a statistically significant advantage.

In vitro resistance to bacterial biofilm formation on coated fluoroplastic tympanostomy tubes.

Bacterial biofilm formation has been implicated in persistent posttympanostomy otorrhea and irreversible tube contamination. The use of a tympanostomy tube with a resistance to biofilm formation by the most common organisms associated with persistent infection may decrease the incidence of chronic otorrhea and the need for tube removal. In this investigation, scanning electron microscopy was used to compare a phosphorylcholine-coated fluoroplastic tympanostomy tube to plain fluoroplastic and silver oxide-impregnated fluoroplastic for resistance to biofilm formation after in vitro incubation with Staphylococcus aureus or Pseudomonas aeruginosa. Only a biofilm from Pseudomonas formed on the untreated fluoroplastic tubes, whereas the silver oxide-impregnated tubes developed biofilms from both S aureus and P aeruginosa. In contrast, the coated fluoroplastic tube showed resistance to both staphylococcal and pseudomonal biofilm adhesion. This is the first study to demonstrate the effect of a surface treatment of fluoroplastic as a method to inhibit biofilm formation by both S aureus and P aeruginosa. This reinforces our previous studies showing that surface-adherence properties such as charge or slickness or both may be more beneficial than antibacterial treatments in preventing film adhesion.

Appropriateness of routine postoperative chest radiography after tracheotomy.

OBJECTIVE: To determine the appropriateness of postoperative chest radiography after adult tracheotomy. DESIGN: Retrospective case series. SETTING: Tertiary care academic medical center. PATIENTS: The records of 379 consecutive adult patients who underwent tracheotomy by the Otolaryngology-Head and Neck Surgery Service from January 1992 to December 1996 were available for review and met inclusion criteria. All patients underwent postoperative chest radiography. MAIN OUTCOME MEASURES: Frequency of postoperative tracheotomy-associated complications, most significantly pneumothorax. RESULTS: The patients had no pneumothorax on postoperative chest films. Minor complications, which were found in 7.1% of the patients, included small bleeds, wound infection, and subcutaneous emphysema. Tracheostomy-associated death occurred in 2 patients (0.5%). CONCLUSIONS: Routine postoperative chest radiography is unnecessary after adult tracheotomy. Chest radiography may be indicated by clinically suspicious signs or symptoms.

Delineation of the regions of interleukin-2 (IL-2) receptor beta chain important for association of Jak1 and Jak3. Jak1-independent functional recruitment of Jak3 to Il-2Rbeta.

Interleukin-2 (IL-2) induces heterodimerization of the IL-2 receptor beta (IL-2Rbeta) and gammac chains of its receptor and activates the Janus family tyrosine kinases, Jak1 and Jak3. Whereas Jak1 associates with IL-2Rbeta, Jak3 associates primarily with gammac but also with IL-2Rbeta. We analyzed four IL-2Rbeta mutations that diminish IL-2-induced proliferation and found that each also decreased IL-2-induced signal transducer and activator of transcription (STAT) activation. For this reason, and because the mutations were in the IL-2Rbeta membrane-proximal region, we investigated and found that each mutation diminished IL-2Rbeta association with both Jak1 and Jak3. This suggested that these Jaks might interact with the same region of IL-2Rbeta; however, certain IL-2Rbeta internal deletions and C-terminal truncations differentially affected the association of Jak1 and Jak3. Interestingly, just as Jak1-IL-2Rbeta association is Jak3-independent and functionally important, we show that Jak3-IL-2Rbeta association is Jak1-independent and implicate this association as being important for IL-2-induced Stat5 activation. Moreover, Jak1 and Jak3 could associate only in the presence of IL-2Rbeta, suggesting that these kinases can simultaneously bind to IL-2Rbeta. Thus, our data not only demonstrate that somewhat more distal as well as membrane-proximal cytoplasmic regions of a type I cytokine receptor are important for Jak kinase association but also suggest that two IL-2Rbeta-Jak kinase interactions are important for IL-2 signaling.

The Regulation of Electron Partitioning between the Cytochrome and Alternative Pathways in Soybean Cotyledon and Root Mitochondria.

The regulation of electron partitioning between the cytochrome (Cyt) and alternative pathways in soybean (Glycine max L. cv Ransom) mitochondria in the absence of added inhibitors has been studied using the oxygen isotope fractionation technique. This regulation can depend on several factors, including the amount of alternative oxidase protein, the redox status of the alternative oxidase regulatory sulfhydryl-disulfide system, the degree of activation by [alpha]-keto acids, and the concentration and redox state of the ubiquinone pool. We studied electron partitioning onto the alternative pathway in mitochondria isolated from etiolated and light-grown cotyledons and roots to ascertain how these factors interact in different tissues. In light-grown cotyledon mitochondria there is some partitioning to the alternative pathway in state 4, which is increased dramatically by either pyruvate or dithiothreitol. In etiolated cotyledon mitochondria, the alternative pathway shows little ability to compete for electrons with the Cyt pathway under any circumstances. In root mitochondria, control of alternative pathway activity is exercised by both the ubiquinone pool and the regulatory sulfhydryl-disulfide system. In addition, oxygen isotope fractionation by the Cyt and alternative pathways in mitochondria were identical to the fractionation for the respective pathways seen in intact tissue, suggesting that residual respiration is not present in the absence of inhibitors.

Cyclic electron flow around Photosystem II in vivo.

The oxygen flash yield (YO2) and photochemical yield of PS II (ΦPS II) were simultaneously detected in intact Chlorella cells on a bare platinum oxygen rate electrode. The two yields were measured as a function of background irradiance in the steady-state and following a transition from light to darkness. During steady-state illumination at moderate irradiance levels, YO2 and ΦPS II followed each other, suggesting a close coupling between the oxidation of water and QA reduction (Falkowski et al. (1988) Biochim. Biophys. Acta 933: 432-443). Following a light-to-dark transition, however, the relationship between QA reduction and the fraction of PS II reaction centers capable of evolving O2 became temporarily uncoupled. ΦPS II recovered to the preillumination levels within 5-10 s, while the YO2 required up to 60 s to recover under aerobic conditions. The recovery of YO2 was independent of the redox state of QA, but was accompanied by a 30% increase in the functional absorption cross-section of PS II (σPS II). The hysteresis between YO2 and the reduction of QA during the light-to-dark transition was dependent upon the reduction level of the plastoquinone pool and does not appear to be due to a direct radiative charge back-reaction, but rather is a consequence of a transient cyclic electron flow around PS II. The cycle is engaged in vivo only when the plastoquinone pool is reduced. Hence, the plastoquinone pool can act as a clutch that disconnects the oxygen evolution from photochemical charge separation in PS II.