Modulation of CHT7 Complexes during Light/Dark- and Nitrogen-Mediated Life Cycle Transitions of Chlamydomonas.

The Chlamydomonas reinhardtii Compromised Hydrolysis of Triacylglycerols7 (CHT7) protein has been previously implicated in the regulation of DNA metabolism and cell-cycle-related gene expression during nitrogen (N) deprivation, and its predicted protein interaction domains are necessary for function. Here, we examined impacts of the cht7 mutation during the cell division cycle under nutrient deficiency in light-dark synchronized cultures. We explored the potential mechanisms affecting CHT7 complex activities during the cell cycle and N starvation, with a focus on the possible interaction between CHT7 and the C. reinhardtii retinoblastoma tumor suppressor (RB) protein homolog MAT3. Notably, the absence of CHT7 did not negatively impact the synchrony of cell division and cell cycle progression during diel growth. Although the majority of CHT7 and MAT3/RB proteins were observed in separate complexes by blue native-PAGE, the two proteins coimmunoprecipitated both during synchronized growth and following N deprivation, suggesting the presence of low abundance subcomplexes containing CHT7 and MAT3/RB. Furthermore, we observed several phosphorylated isoforms of CHT7 under these conditions. To test the potential role of phosphorylation on the structure and function of CHT7, we performed site-directed mutagenesis of previously identified phosphorylated amino acids within CHT7. These phosphorylated residues were dispensable for CHT7 function, but phosphorylated variants of CHT7 persisted, indicating that yet-unidentified residues within CHT7 are also likely phosphorylated. Based on the interaction of CHT7 and MAT3/RB, we postulate the presence of a low-abundance or transient regulatory complex in C. reinhardtii that may be similar to DREAM-like complexes in other organisms.

Lung function deterioration in school children with cystic fibrosis.

INTRODUCTION: Lung disease in cystic fibrosis (CF) begins early in life but the capabilities for detecting abnormalities of pulmonary dysfunction in children remain limited. OBJECTIVE: The study aimed to evaluate the early progression of lung function by the analysis of pulmonary hyperinflation, ventilation inhomogeneity (VI), trapped gas and airway obstruction with age. METHODS: One hundred CF children aged 7 to 18, divided into two groups aged 7 to 12 (n = 40) and 13 to 18 (n = 60), were enrolled. Patients performed multiple-breath nitrogen washout (MBNW) tests and plethysmography for measurements of lung clearance index (LCI), functional residual capacity (FRCpleth , FRCMBNW ), volume of trapped gas (VT ), total resistance, and effective and specific effective airway resistance (Reff , sReff ). RESULTS: We obtained a positive correlation of FRCpleth , FRCMBNW , and LCI with age. A linear correlation between FRCMBNW and FRCpleth (P < .0001) was observed. VI was higher in the group of older patients (9.79 in the group aged 7-12 and 11.67 in the group aged 13-18). An increased effective specific airway resistance >2 (z-score) was present in 58% of all subjects (50% and 63.3%, respectively). Pulmonary hyperinflation (FRCpleth >2 z-score) was observed in 33% of all patients: 25% and 36.6%, respectively. Trapped gas (VT > 2 z-score) was present in 18% of all children: 30% and 10%, respectively. CONCLUSION: A gradual decline in lung function is associated with an increase in VI, airway obstruction, pulmonary hyperinflation and development of trapped gas. In children who cannot perform either spirometry or plethysmography, MBNW can deliver a measurement of LCI connecting with VI as well as FRCMBNW to indicate indirectly the increase of hyperinflation.

Plant Biodiversity Change Across Scales During the Anthropocene.

Plant communities have undergone dramatic changes in recent centuries, although not all such changes fit with the dominant biodiversity-crisis narrative used to describe them. At the global scale, future declines in plant species diversity are highly likely given habitat conversion in the tropics, although few extinctions have been documented for the Anthropocene to date (<0.1%). Nonnative species introductions have greatly increased plant species richness in many regions of the world at the same time that they have led to the creation of new hybrid polyploid species by bringing previously isolated congeners into close contact. At the local scale, conversion of primary vegetation to agriculture has decreased plant diversity, whereas other drivers of change-e.g., climate warming, habitat fragmentation, and nitrogen deposition-have highly context-dependent effects, resulting in a distribution of temporal trends with a mean close to zero. These results prompt a reassessment of how conservation goals are defined and justified.

Arabidopsis cryptochrome 1 functions in nitrogen regulation of flowering.

The phenomenon of delayed flowering after the application of nitrogen (N) fertilizer has long been known in agriculture, but the detailed molecular basis for this phenomenon is largely unclear. Here we used a modified method of suppression-subtractive hybridization to identify two key factors involved in N-regulated flowering time control in Arabidopsis thaliana, namely ferredoxin-NADP(+)-oxidoreductase and the blue-light receptor cryptochrome 1 (CRY1). The expression of both genes is induced by low N levels, and their loss-of-function mutants are insensitive to altered N concentration. Low-N conditions increase both NADPH/NADP(+) and ATP/AMP ratios, which in turn affect adenosine monophosphate-activated protein kinase (AMPK) activity. Moreover, our results show that the AMPK activity and nuclear localization are rhythmic and inversely correlated with nuclear CRY1 protein abundance. Low-N conditions increase but high-N conditions decrease the expression of several key components of the central oscillator (e.g., CCA1, LHY, and TOC1) and the flowering output genes (e.g., GI and CO). Taken together, our results suggest that N signaling functions as a modulator of nuclear CRY1 protein abundance, as well as the input signal for the central circadian clock to interfere with the normal flowering process.

[Effects of purified humic acid on growth and nutrient absorption of cucumber (Cucumis sativus)seedlings under low nitrogen stress.] / çº¯åŒ–è æ¤é ¸å¯¹ä½Žæ°®èƒè¿«ä¸‹é»„ç“œå¹¼è‹—ç”Ÿé•¿åŠå »åˆ†å¸æ”¶çš„å½±å“.

Taking 'Xintaimici' and 'Jinyou 1' as experimental cucumber cultivars, this paper studied the effects of watering purified humic acid (PHA) at different levels (0, 50, 100, 150, 200 mg·L-1) on growth and nutrient absorption of cucumber seedlings under low nitrogen stress (1 mmol·L-1 NO3-) in sand culture pots. The results showed that, under low N condition, PHA could significantly increase the total root length, root surface area, root tip number and root volume of cucumber seedlings, and promote plant height, stem diameter and leaf area. Proline and soluble sugar contents in cucumber leaves were significantly increased by PHA. The absorption of N, P, K, Ca, Mg, Fe in cucumber seedlings was promoted. According to the response of the two cucumber cultivars to PHA under low N stress, some traits of two cultivars showed different sensitivity to PHA level. The comprehensive analysis of the above results inferred that the PHA level from 100 mg·L-1 to 150 mg·L-1 could significantly enhance the growth and nutrient absorption of cucumber seedlings.

Oxandrolone use in adult burn patients. Systematic review and meta-analysis

PURPOSE: This study is a systematic literature review and meta-analysis concerning the use of a testosterone synthetic analog, oxandrolone, and its use in severe adult burns. METHODS: Randomized prospective clinical studies, in English, Portuguese or Spanish, were sought on the following databases: MEDLINE, COCHRANE, EMBASE and LILACS. There was no restriction in relation to the publication date. RESULTS: This search produced 24 studies on MEDLINE and twelve articles were presented on the COCHRANE database .Sixteen were excluded due to the title not being related to this search or by including children. Of the eigth residual studies, after adaptation to the inclusion criteria, only four were selected. After analyzing the results, two were discarded since they did not present adequate patient characterization and the facts on these articles were analyzed differently from the others, hindering the meta-analysis. CONCLUSION: The analysis of the available data demonstrated significant benefits (p<0.05) considering lesser loss of corporal mass, lesser nitrogen loss, and shorter donor area healing time, when Oxandrolone was used, comparatively with the control group (placebo or not). .

The role of the ubiquitin-proteasome system in the response of the ligninolytic fungus Trametes versicolor to nitrogen deprivation.

The white rot fungus Trametes versicolor is an efficient lignin degrader with ecological significance and industrial applications. Lignin-modifying enzymes of white rot fungi are mainly produced during secondary metabolism triggered in these microorganisms by nutrient deprivation. Selective ubiquitin/proteasome-mediated proteolysis is known to play a crucial role in the response of cells to various stresses such as nutrient limitation, heat shock, and heavy metal exposure. Previous studies from our laboratory demonstrated that proteasomal degradation of intracellular proteins is involved in the regulation of laccase, a major ligninolytic enzyme of T. versicolor, in response to cadmium. In the present study, it was found that the 6-h nitrogen starvation leads to depletion of intracellular free ubiquitin pool in T. versicolor. The difference in the intracellular level of free monomeric ubiquitin observed between the mycelium extract from the nitrogen-deprived and that from the nitrogen-sufficient culture was accompanied by the different pattern of ubiquitin-dependent degradation. Furthermore, it was found that nitrogen deprivation affected 26S proteasome activities of T. versicolor. Proteasome inhibition by lactacystin beta-lactone, a highly specific agent, increased laccase activity in nitrogen-deprived cultures, but not in nitrogen-sufficient cultures. The present study implicates the ubiquitin/proteasome-mediated proteolytic pathway in the response of T. versicolor to nitrogen deprivation.

Cyanobacterial heterocysts: terminal pores proposed as sites of gas exchange.

In many filamentous cyanobacteria, oxygenic photosynthesis is restricted to vegetative cells, whereas N(2) fixation is confined to microoxic heterocysts. The heterocyst has an envelope that provides a barrier to gas exchange: N(2) and O(2) diffuse into heterocysts at similar rates, which ensures that concentrations of N(2) are high enough to saturate N(2) fixation while respiration maintains O(2) at concentrations low enough to prevent nitrogenase inactivation. I propose that the main gas-diffusion pathway is through the terminal pores that connect heterocysts with vegetative cells. Transmembrane proteins would make the narrow pores permeable enough and they might provide a means of regulating the rate of gas exchange, increasing it by day, when N(2) fixation is most active, and decreasing it at night, minimizing O(2) entry. Comparisons are made with stomata, which regulate gas exchange in plants.

Feedback control of morphogenesis in fungi by aromatic alcohols.

Many fungi undergo a developmental transition from a unicellular yeast form to an invasive filamentous form in response to environmental cues. Here we describe a quorum signaling pathway that links environmental sensing to morphogenesis in Saccharomyces cerevisiae. Saccharomyces cells secrete aromatic alcohols that stimulate morphogenesis by inducing the expression of FLO11 through a Tpk2p-dependent mechanism. Mutants defective in synthesis of these alcohols show reduced filamentous growth, which is partially suppressed by the addition of these aromatic alcohols. The production of these auto signaling alcohols is regulated by nitrogen: High ammonia restricts it by repressing the expression of their biosynthetic pathway, whereas nitrogen-poor conditions activate it. Moreover, the production of these aromatic alcohols is controlled by cell density and subjected to positive feedback regulation, which requires the transcription factor Aro80p. These interactions define a quorum-sensing circuit that allows Saccharomyces to respond to both cell density and the nutritional state of the environment. These same autoregulatory molecules do not evoke the morphological switch in Candida albicans, suggesting that these molecular signals are species-specific.

Cadmium toxicity to two marine phytoplankton under different nutrient conditions.

Cd accumulation and toxicity in two marine phytoplankton (diatom Thalassiosira weissflogii and dinoflagellate Prorocentrum minimum) under different nutrient conditions (nutrient-enriched, N- and P-starved conditions) were examined in this study. Strong interactions between the nutrients and Cd uptake by the two algal species were found. Cd accumulation as well as N and P starvation themselves inhibited the assimilation of N, P, and Si by the phytoplankton. Conversely, N starvation strongly inhibited Cd accumulation but no influence was observed under P starvation. However, the Cd accumulation difference between nutrient-enriched and N-starved cells was smaller when [Cd(2+)] was increased in the medium, indicating that net Cd accumulation was less dependent on the N-containing ligands at high-Cd levels. As for the subcellular distribution of the accumulated Cd, most was distributed in the insoluble fraction of T. weissflogii while it was evenly distributed in the soluble and insoluble fractions of P. minimum at low-Cd levels. A small percentage of cellular Cd (<15%) was adsorbed on the cell surface for both algae at the lowest [Cd(2+)], which increased when the [Cd(2+)] increased. Cd toxicity in phytoplankton was quantified as depression of growth and maximal photosynthetic system II quantum yield, and was correlated with the [Cd(2+)], intracellular Cd concentration, and Cd concentrations in the cell-surface-adsorbed, soluble, and insoluble fractions. According to the estimated median inhibition concentration (IC50) based on the different types of Cd concentration, the toxicity difference among the different nutrient-conditioned cells was the smallest when the Cd concentration in the soluble fraction was used, suggesting that it may be the best predictor of Cd toxicity under different nutrient conditions.

The 3' untranslated region of a soybean cytosolic glutamine synthetase (GS1) affects transcript stability and protein accumulation in transgenic alfalfa.

Higher plants assimilate nitrogen in the form of ammonia through the concerted activity of glutamine synthetase (GS) and glutamate synthase (GOGAT). The GS enzyme is either located in the cytoplasm (GS1) or in the chloroplast (GS2). Glutamine synthetase 1 is regulated in different plants at the transcriptional level and there are some reports of regulation at the level of protein stability. Here we present data that clearly establish that GS1 in plants is also regulated at the level of transcript turnover and at the translational level. Using a Glycine max (soybean) GS1 transgene, with and without its 3' untranslated region (UTR), driven by the constitutive CaMV 35S promoter in Medicago sativa (alfalfa) and Nicotiana tabacum (tobacco), we show that the 3' UTR plays a major role in both transcript turnover and translation repression in both the leaves and the nodules. Our data suggest that the 3' UTR mediated turnover of the transcript is regulated by a nitrogen metabolite or carbon/nitrogen ratios. We also show that the 3' UTR of the gene for the soybean GS1 confers post-transcriptional regulation on a reporter gene. Our dissection of post-transcriptional and translational levels of regulation of GS in plants shows that the situation in plants strongly resembles that in other organisms where GS is regulated at almost all levels. Multistep regulation of GS shows the high priority given by organisms to regulating and ensuring optimal control of nitrogen substrates and preventing overproduction of glutamine and drainage of the glutamate pool.

Identification and expression analysis of two inorganic C- and N-responsive genes encoding novel and distinct molecular forms of eukaryotic phosphoenolpyruvate carboxylase in the green microalga Chlamydomonas reinhardtii.

Phosphoenolpyruvate carboxylase (PEPC [Ppc]) has been previously purified and characterized in biochemical and immunological terms from two green microalgae, Chlamydomonas reinhardtii and Selenastrum minutum. The findings indicate that these algae possess at least two distinct PEPC enzyme-forms, homotetrameric Class-1 and heteromeric Class-2, that differ significantly from each other and their plant and prokaryotic counterparts. Surprisingly, however, green-algal PEPC has been unexplored to date in molecular terms. This study reports the molecular cloning of the two Ppc genes in C. reinhardtii (CrPpc1, CrPpc2), each of which is transcribed in vivo and encodes a fully active, recombinant PEPC that lacks the regulatory, N-terminal seryl-phosphorylation domain that typifies the vascular-plant enzyme. These distinct catalytic subunit-types differ with respect to their (i) predicted molecular mass ( approximately 108.9 [CrPpc1] versus approximately 131.2 kDa [CrPpc2]) and critical C-terminal tetrapeptide; and (ii) immunoreactivity with antisera against the p102 and p130 polypeptides of S. minutum PEPC1/PEPC2 and PEPC2, respectively. Only the Ppc1 transcript encodes the p102 catalytic subunits common to both Class-1 and Class-2 enzyme-forms in C. reinhardtii. The steady-state transcript levels of both CrPpc1/2 are coordinately up-/down-regulated by changes in [CO2] or [NH] during growth, and generally mirror the response of cytoplasmic glutamine synthetase (Gs1) transcript abundance to changes in inorganic [N] at 5% CO2. These collective findings provide key molecular insight into the Ppc genes and corresponding PEPC catalytic subunits in the eukaryotic algae.

The role of alternative oxidase in modulating carbon use efficiency and growth during macronutrient stress in tobacco cells.

When wild-type (wt) tobacco (Nicotiana tabacum cv. Petit Havana SR1) cells are grown under macronutrient (P or N) limitation, they induce large amounts of alternative oxidase (AOX), which constitutes a non-energy-conserving branch of the respiratory electron transport chain. To investigate the significance of AOX induction, wt cells were compared with transgenic (AS8) cells lacking AOX. Under nutrient limitation, growth of wt cell cultures was dramatically reduced and carbon use efficiency (g cell dry weight gain g(-1) sugar consumed) decreased by 42-63%. However, the growth of AS8 was only moderately reduced by the nutrient deficiencies and carbon use efficiency values remained the same as under nutrient-sufficient conditions. As a result, the nutrient limitations more severely compromised the tissue nutrient status (P or N) of AS8 than wt cells. Northern analyses and a comparison of the mitochondrial protein profiles of wt and AS8 cells indicated that the lack of AOX in AS8 under P limitation was associated with increased levels of proteins commonly associated with oxidative stress and/or stress injury. Also, the level of electron transport chain components was consistently reduced in AS8 while tricarboxylic acid cycle enzymes did not show a universal trend in abundance in comparison to the wt. Alternatively, the lack of AOX in AS8 cells under N limitation resulted in enhanced carbohydrate accumulation. It is concluded that AOX respiration provides an important general mechanism by which plant cells can modulate their growth in response to nutrient availability and that AOX also has nutrient-specific roles in maintaining cellular redox and carbon balance.

Catabolismo muscular nos pacientes com infarto agudo do moicárdio / Muscular catabolism in patients with acute myocardial infarction

Introdução: O trauma e a sepse apresentam demanda metabólica aumentada devido à tríplice liberação hormonal com consequente aumento do catabolismo muscular. O infarto agudo do miocárdio(IAM) também pode ser considerado um trauma por apresentar as alterações hormonais características da fase aguda do estresse.Objetivo: Avaliar o grau de catabolismo muscular, quantificado pela excreção urinária de nitrogênio uréico em urina de 24 horas, nos pacientes admitidos com IAM.Métodos: Analisados prospectivamente 22 pacientes internados com IAM, sendo 12 de parede inferior e 10 de anterior, caracterizados elétrica e bioquimicamente com injúria e necrose transmural. A área do infarto foi diagnosticada pelo eletrocardiograma e confirmada pelas alterações no ecocardiograma. Foram excluídos os pacientes com insuficiência renal, IAM não transmural(ausência da onda Q evolutiva) e aqueles com mais de 48 horas de IAM. A coleta de urina de 24 horas foi realizada no 1º, 3º e 5º dias de internação para a quantificação da uréia excretada. O nitrogênio urinário foi calculado a partir da uréia, considerando-se um percentual nitrogendo de 46.66 por cento na molécula uréica. A avaliação estatística foi realizada pela análise de variância two way e pelo teste de Tukey, com nível de significância de 5 po cento.Resultados: O IAM, tanto anterior como inferior, apresenta catabolismo muscular evolutivo(terceiro dia) caracterizado como moderado(N2Dia3/Dia1, p igual 0,001). O catabolismo muscular foi idêntico mo IAM anterior e inferior (p igual 0,49). O catabolismo muscular é revertido no quinto dia.Conclusão: Os pacientes com IAM apresentaram um aumento reversível do catabolismo muscular

Stress-induced changes in protease composition are determined by nitrogen supply in non-nodulating white clover.

An inbreeding line of white clover has been identified which remains non-nodulated under appropriate physiological conditions and so the nitrogen concentration of the plant can be manipulated by altering the nitrate supply to the roots. Non-nodulating plants were used to test the hypothesis that acclimation to nitrogen limitation in white clover involves changes in protease activity and composition. These results indicate that acclimation to nitrogen limitation involves the realignment of constituent proteases without necessarily incurring significant changes in total protease activity. Plants grown at 2.5, 5.0, 7.5, and 10 mM nitrate showed a positive correlation between nitrate supply and foliar protein concentration. Protein profiles, revealed by Coomassie-stained SDS-PAGE, were unchanged between treatments for a given amount of protein. Serine, aspartate/metalloprotease, and two cysteine proteases were identified in the leaves. Although total protease activity per gram fresh weight was unchanged between treatments, the relative contributions of these four proteases was determined by nitrate supply. When plants were stressed further by withholding nitrate there was an increase in cysteine protease activity, but a senescence-related aspartate/metalloprotease was not visible. Hence, while protease expression in white clover leaves responded to the current and past nitrogen status of the plant, the proteases involved in remobilization during nutrient limitation were distinct from those involved during the main senescence period. It is suggested that nitrogen limitation induced an early, reversible stage of senescence in which perturbations in protease activity facilitated the degradation of non-essential proteins in order to increase the chances of plant survival or seed set.

Leaf chlorophyll, net gas exchange and chloroplast ultrastructure in citrus leaves of different nitrogen status.

One-year-old 'Cleopatra mandarin' (Citrus reticulata Blanco) seedlings were raised in a greenhouse and fertilized with nitrogen (N) at four application frequencies. Nitrogen-deficient leaves (86 mmol N m-2) had less chlorophyll per unit area, but a greater chlorophyll a:b ratio than N-fertilized leaves (> 187 mmol N m-2). Leaf dry mass per area (DM area-1) and total chlorophyll concentration increased linearly with increasing leaf N, whereas chlorophyll a:b ratio declined. Net assimilation of CO2 (A(CO2)) and leaf water-use efficiency (WUE) reached maximum values in leaves with approximately 187 mmol N m-2. Nitrogen-deficient leaves exhibited small chloroplasts with no starch granules; grana and stroma lamellae that coincided with the accretion of numerous large plastoglobuli in the stroma disintegrated. High-N leaves had large chloroplasts with well-developed grana, stroma lamellae and starch granules that enlarged with increasing N concentration. The lack of an increase in A(CO2) capacity at leaf N concentrations above 187 mmol N m-2 appeared to be correlated with the presence of numerous large starch granules.

The response of Leuconostoc mesenteroides to low external oxidoreduction potential generated by hydrogen gas.

AIMS: The physiological consequences of low external oxidoreduction potential in Leuconostoc mesenteroides were investigated. METHODS AND RESULTS: Leuconostoc mesenteroides was grown under two initial oxidoreduction potential conditions (Eh7: +200 mV and -400 mV) using nitrogen and hydrogen as reducing agents. Growth was affected by Eh7; the lag phase increased from 1 h at an initial Eh7 of +200 mV to 6 h at an initial Eh7 of -400 mV; the maximum specific growth rate at -400 mV was 68% of the one observed at +200 mV. The NADH/NAD+ ratio and (NADH + NAD+) pool were independent of the external Eh7. CONCLUSIONS: This study shows that changing the external oxidoreduction potential from +200 to -400 mV has a strong effect on the Leuc. mesenteroides physiology. The constancy of the maximum carbon and energetic fluxes (qglu, qATP) under the two Eh7 conditions accompanied by the decrease of YX/S and YATP suggested the existence of an uncoupling phenomenon, namely that some catabolized glucose and hence ATP was not associated with biomass production. SIGNIFICANCE AND IMPACT OF THE STUDY: This paper demonstrates the usefulness of taking into account, the effect of the oxidoreduction potential on the growth of Leuc. mesenteroides in the fermentation process.

Effects of gas conditions, time of medium change, and ratio of medium to embryo on in vitro development of horse oocytes fertilized by intracytoplasmic sperm injection.

This study was conducted to evaluate the effects of two different gas conditions (5% CO(2) in air or 5% CO(2), 5% O(2), 90% N(2), mixed gas), time of medium change (Day 3 or 4) and ratio of medium to embryo (2, 5 or 10 microl per presumptive zygote) on the development of horse oocytes fertilized by intracytoplasmic sperm injection and cultured in G1.2/2.2 medium. Oocytes from slaughterhouse-derived ovaries were matured in vitro for 24 h and fertilized by injection of frozen-thawed sperm using micromanipulation with a Piezo drill. Presumptive zygotes were randomly assigned to 5% CO(2) in air or mixed gas and fixed after 96 h of culture. Cleavage rates between two gas conditions were similar (67 and 63%), but the mean nucleus number of embryos in the mixed gas treatment was significantly (P<0.05) higher than that of embryos cultured in 5% CO(2) in air (15.2 versus 7.0, respectively). Further experiments were done with mixed gas incubation. Development of embryos was compared after change from G1.2 to G2.2 medium at Day 3 or 4. There was no significant difference in cleavage rate (56 and 65%, respectively) or development to the blastocyst stage after 7 days of culture (5% and 46%, respectively) between embryos changed on different days. To evaluate the effect of the ratio of medium to embryo, zygotes were cultured at a ratio of 2, 5 or 10 microl medium per zygote. There were no significant differences among ratio treatments in rates of cleavage or development to blastocyst.

Soil temperature, gas exchange and nitrogen status of 5-year-old Norway spruce seedlings.

Five-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment chambers. Plants were acclimated to a soil temperature of 16 degrees C during the first and third growing seasons, but were allocated at random to soil temperature treatments of 9, 13, 18 and 21 degrees C during the second growing season. Low soil temperature during the second growing season depressed stomatal conductance and photosynthetic rate (A) per unit of projected leaf area, although intercellular CO2 concentrations did not differ significantly between treatments. At all soil temperatures, total chlorophyll concentration first decreased and then increased, although the rate of increase and the final concentration increased with soil temperature, which may explain the effect of soil temperature on A. Neither chlorophyll a/b ratio nor leaf nitrogen concentration was significantly affected by soil temperature. Treatment differences disappeared during the third simulated growing season when plants were again acclimated to a soil temperature of 16 degrees C.

Physiological gas exchange in the middle ear cavity.

OBJECTIVES: Many reports pointed out that gas exchange in and out of the middle ear cavity occurs not only via the Eustachian tube but also across the middle ear mucosa. Our earlier study on children with otitis media with effusion (OME) for which a tympanic ventilation tube (TUBE) had been inserted revealed that the more severe the inflammatory change of the middle ear mucosa, the higher the degree of impairment of the transmucosal gas exchange function and the greater the decrease in the middle ear total pressure (METP). We hypothesized that the change in METP is caused by gas migration, and we conducted the present animal study to test this hypothesis and to determine the importance of METP measurement. MATERIALS AND METHODS: Using 30 rabbits, ten in a group in which the middle ear cavity gas was replaced with atmospheric air (Group 1, oxygen (O(2)) 20%, carbon dioxide (CO(2)) 0.03% and nitrogen (N(2)) 79.9%), ten in a group replaced with a high CO(2) pressure gas whose partial pressure of CO(2) only was increased to 5% (Group 2, O(2) 20%, CO(2) 5% and balanced with N(2)) and ten in a group replaced with a low O(2) pressure gas (Group 3, O(2) 5%, CO(2) 0.03% and balanced with N(2)), changes in the METP were measured. RESULTS: Group 1 showed a pressure change (increase, peak and then decrease in the METP) similar to that observed in a clinical cured group of OME with TUBE. In Group 2, no increase in the METP was observed and in Group 3 increase in the METP was observed but no decrease in the METP was observed. CONCLUSIONS: It was found that the increase in the METP is attributable to diffusion of CO(2). This study elucidated that the change in the METP is a physiological response. Since the METP correlates with the degree of histologic inflammatory change in the middle ear mucosa, which was revealed in our clinical study of OME, it was reconfirmed that measurement of the METP is an important test method for evaluation of the degree of improvement in the pneumatic cavity mucosa.