植物气孔导度对CO2响应模型的构建

构建一个普适性的植物叶片气孔导度(g_s)对CO₂浓度响应(g_s-C_a)的模型, 对定量研究植物叶片g_s对CO₂浓度的响应变化尤为必要。该研究运用便携式光合仪(LI-6400)测量了大豆(Glycine max)和小麦(Triticum aestivum)光合作用对CO₂的响应曲线(A_n-C_a), 在比较传统的Michaelis-Menten模型(M-M模型)和叶子飘构建的CO₂响应模型拟合大豆和小麦A_n-C_a效果的基础上, 构建了g_s-C_a响应新模型。然后用新构建的模型拟合大豆和小麦的g_s-C_a曲线, 并将拟合结果与传统模型的拟合结果, 以及与其对应的观测数据进行比较, 以判断所构建模型是否合理。结果显示: 叶子飘构建的A_n-C_a模型可较好地拟合大豆和小麦的A_n-C_a曲线, 确定系数(R²)均高达0.999。M-M模型拟合大豆和小麦的A_n-C_a曲线时的R²虽然也较高, 但在较高CO₂浓度时的拟合曲线偏离观测曲线。因此, 基于叶子飘的A_n-C_a模型构建g_s-C_a模型更为可行。新构建的g_s-C_a模型可较好地拟合大豆和小麦的g_s-C_a曲线, R²分别为0.995和0.994, 而且还可以直接给出最大气孔导度(g_s-max)、最小气孔导度(g_s-min), 以及与g_s-min相对应的CO₂浓度值(C_s-min)。拟合得到大豆和小麦的g_s-max分别为0.686和0.481 mol·m^-2·s^-1, 与其对应的观测值(分别为0.666和0.471 mol·m^-2·s^-1)之间均不存在显著差异; 同样, 拟合得到的大豆和小麦的g_s-min分别为0.271和0.297 mol·m^-2·s^-1, 与其对应的观测值(分别为0.279和0.293 mol·m^-2·s^-1)之间也均不存在显著差异; 此外, 新构建的g_s-C_a模型给出大豆和小麦的C_s-min值分别为741.45和1 112.43 μmol·mol ^-1, 与其对应的观测值(732.78和1 200.34 μmol·mol ^-1)也不存在显著差异。由此可见, 该研究新构建的g_s-C_a模型可作为定量研究植物叶片气孔导度对CO₂浓度变化的有效数学工具。     

Construction of CO2-response model of electron transport rate in C4 crop and its application

准确估算光合电子流对CO₂响应的变化趋势对深入了解光合过程具有重要意义。该研究在植物光合作用对CO₂响应新模型(模型I)的基础上构建了电子传递速率(J)对CO₂的响应模型(模型II), 并对用LI-6400-40便携式光合仪测量的玉米(Zea mays)和千穗谷(Amaranthus hypochondriacus)的数据进行了拟合。结果表明, 模型II可以很好地拟合玉米和千穗谷叶片J对CO₂浓度的响应曲线(J-C_a曲线), 得到玉米和千穗谷的最大电子传递速率分别为262.41和393.07 mmol·m ^-2·s ^-1, 与估算值相符合。在此基础上, 对光合电子流分配到其他路径进行了探讨。结果显示, 380 mmol·mol ^-1 CO₂浓度下玉米和千穗谷碳同化所需的电子流为247.92和285.16 mmol·m ^-2·s ^-1, 分配到其他途径的光合电子流为14.49和107.91 mmol·m ^-2·s ^-1(考虑植物CO₂的回收利用)。比较两种植物的其他途径光合电子流分配值发现, 两者相差6倍之多。分析认为这与千穗谷和玉米的催化脱羧反应酶种类以及脱羧反应发生的部位不同密切相关。该发现为人们研究C₄植物中烟酰胺腺嘌呤二核苷磷酸苹果酸酶型和烟酰胺腺嘌呤二核苷酸苹果酸酶型两种亚型之间的差异提供了一个新的视角。此外, 构建的电子传递速率对CO₂的响应模型为人们研究C₄植物的光合电子流的变化规律提供了一个可供选择的数学工具。     

Generalized T2 test for genome association studies

Recent progress in the development of single-nucleotide polymorphism (SNP) maps within genes and across the genome provides a valuable tool for fine-mapping and has led to the suggestion of genomewide association studies to search for susceptibility loci for complex traits. Test statistics for genome association studies that consider a single marker at a time, ignoring the linkage disequilibrium between markers, are inefficient. In this study, we present a generalized T2 statistic for association studies of complex traits, which can utilize multiple SNP markers simultaneously and considers the effects of multiple disease-susceptibility loci. This generalized T2 statistic is a corollary to that originally developed for multivariate analysis and has a close relationship to discriminant analysis and common measure of genetic distance. We evaluate the power of the generalized T2 statistic and show that power to be greater than or equal to those of the traditional chi2 test of association and a similar haplotype-test statistic. Finally, examples are given to evaluate the performance of the proposed T2 statistic for association studies using simulated and real data.     

Maternal proximity and infant CO2 environment during bedsharing and possible implications for SIDS research

Sudden infant death syndrome (SIDS) is the leading cause of human infant mortality after the neonatal period in Western countries. Recently, child care practices have been shown to be important in determining infant vulnerability to SIDS. However, very little is known about the impact of parent-infant cosleeping on infant sleep physiology and behavior and SIDS risk. This reflects the failure of Western societal research paradigms to appreciate the human infant's evolutionary history of cosleeping, the recency of the emergence of solitary infant sleeping as a practice and the fact that parent-infant cosleeping is still the preferred sleeping arrangement for the majority of contemporary societies. Incorporating current hypotheses on the mechanisms of SIDS, we have hypothesized that the comparatively sensory-rich cosleeping environment might be protective against SIDS in some contexts. As a first step to characterize cosleeping environments, this investigation is aimed at assessing, in routinely bedsharing mothers and infants, their relative sleeping positions and the potential for sleeping in close face-to-face proximity and for infant exposure to increased environmental CO2 produced by maternal respiration. The latter is important in that breathing elevated levels of CO2 can have diverse effects, ranging from respiratory stimulation at low levels to suffocation at very high levels. Two related laboratory studies were performed. In the first, all-night videotapes of 12 healthy, routinely bedsharing mother-infant pairs were analyzed for sleeping positions and time spent in face-to-face orientation and distances separating their faces. Infants were 11–15 wk old. Mothers predominantly positioned themselves on their sides facing their infants, with the infants placed either supine or on their sides. Mothers and infants slept oriented face-to-face for 64 ± 27% (S.D.) of non-movement time, with distances less than 20 cm commonly separating their faces. In the second study, concentrations of CO2 in air were measured in six young women at distances of up to 21 cm from their nares. Peak expiratory CO2 concentrations remained above 1.0% at distances up to 9 cm and above 0.5% at 18 cm. Both baseline and peak CO2 levels were further increased at all distances when measured within a partial air pocket created to simulate a bedding environment sometimes seen during bedsharing. We conclude that during bedsharing there is potential for 1) a high degree of face-to-face orientation and close proximity and consequently 2) increased environmental CO2, as a result of maternal respiration, to non-lethal levels that might stimulate infant respiration. The close proximity would also maximize the sensory impact of the mother on the infant through other modalities. We also suggest that bedsharing may minimize prone infant positioning, a known risk factor for SIDS. Am J Phys Anthropol 103:315–328, 1997. © 1997 Wiley-Liss, Inc.     

Development and evaluation of an online CO(2) evolution test and a multicomponent biodegradation test system

Well-established biodegradation tests use biogenously evolved carbon dioxide (CO(2)) as an analytical parameter to determine the ultimate biodegradability of substances. A newly developed analytical technique based on the continuous online measurement of conductivity showed its suitability over other techniques. It could be demonstrated that the method met all criteria of established biodegradation tests, gave continuous biodegradation curves, and was more reliable than other tests. In parallel experiments, only small variations in the biodegradation pattern occurred. When comparing the new online CO(2) method with existing CO(2) evolution tests, growth rates and lag periods were similar and only the final degree of biodegradation of aniline was slightly lower. A further test development was the unification and parallel measurement of all three important summary parameters for biodegradation--i.e., CO(2) evolution, determination of the biochemical oxygen demand (BOD), and removal of dissolved organic carbon (DOC)--in a multicomponent biodegradation test system (MCBTS). The practicability of this test method was demonstrated with aniline. This test system had advantages for poorly water-soluble and highly volatile compounds and allowed the determination of the carbon fraction integrated into biomass (heterotrophic yield). The integrated online measurements of CO(2) and BOD systems produced continuous degradation curves, which better met the stringent criteria of ready biodegradability (60% biodegradation in a 10-day window). Furthermore the data could be used to calculate maximal growth rates for the modeling of biodegradation processes.     

Single breath of CO2 as a clinical test of the peripheral chemoreflex

Peripheral chemoreceptor responsiveness is usually examined clinically by hypoxic testing, but the usefulness of this approach is limited by safety considerations, and the interpretation of results may be confounded by the direct central nervous system effects of hypoxia. Therefore we examined the single-breath (SB) CO2 test to determine its reproducibility and applicability as a clinical test of peripheral chemoreceptor function. The technique involved the inhalation of a SB of 13% CO2 in air. The ventilatory response was determined from the increase in ventilation (VE) during the first 20 s after the test breath and from the difference in end-tidal PCO2 between the test breath and preceding control breaths. The peak increase in VE occurred during the second or third breath after the test breath, corresponding to a delay of approximately 10 s. The mean of 10 SB tests administered at 2- to 3-min intervals was taken as the subject's response. Five healthy subjects were tested in this manner on each of 6 consecutive days with the response having an interday coefficient of variation of 25 +/- 6% (SD). The response in 26 healthy females (aged 22-61 yr) was 0.32 +/- 0.11 l.min-1.Torr-1, and in 26 healthy males (aged 24-69 yr) the response was 0.38 +/- 0.14 (P NS). No significant correlation was found between the age of the subjects and their ventilatory response. Thirty-six of the subjects also underwent hyperoxic CO2 rebreathing tests, the response to which is dependent on central chemoreceptor function. No correlation was found between rebreathing and SB tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

Validation of a Photosynthesis Model through the Use of the CO2Balance of a Greenhouse Tomato Canopy

Several leaf photosynthesis models were developed from wellcontrolled experiments in growth chambers. However, only a fewhave been validated under greenhouse conditions for their quantitativeand qualitative adequacy. In this paper, rates of net photosynthesisfor a tomato crop (Lycopersicon esculentum Mill) were measuredin a semi-commercial greenhouse (615 m³) for a significant timeperiod. Concomitant measurements of climatic conditions andLAI were used for simulation of net photosynthesis using theTOMGRO model which integrates Acock's model for photosynthesiscalculations. From simulations and from sensitivity analysis,the prediction of net photosynthesis appeared to be very sensitiveto the quantum use efficiency. The Acock model with originalparameters underestimated the net photosynthesis rate, but anincrease in the quantum use efficiency by 10% gave a good fit.In an effort to generalize the validity of the model, a residualanalysis was performed and showed a systematic bias relatedto light intensity intercepted by the canopy. The Marquardtalgorithm was used to adjust our data to the model but did noteliminate residual heterogeneity of variance with new parametervalues. On the basis of collected data, the criteria of goodnessof fit used showed that the photosynthesis model is inadequatein describing the CO₂-balance of the greenhouse agrosystem.However, it was determined that it could be used as a submodelwithin a more complex model for predicting growth and development.Copyright 1999 Annals of Botany Company Greenhouse, CO₂-balance, photosynthesis, TOMGRO model, Acock's model, residuals, tomato Lycopersicon esculentum Mill.     

Transient ventilatory response to CO2 as a function of sleep state in full-term infants

The influence of sleep state on the transient (i.e., initial 60 s) and steady-state ventilatory responses to 2% CO2 inhalation was studied in 19 healthy full-term infants. A nasal mask pneumotachometer was used to measure ventilation and end-tidal CO2 partial pressure (PCO2) and enabled abrupt changes in the inspired gas concentration to be made. The magnitude of the change in minute ventilation for both the transient and steady-state responses to CO2 was not statistically different between active (AS) and quiet (QS) sleep. Nonetheless the greater variability in minute ventilation during AS compared with QS continued throughout the period of CO2 inhalation and was associated with a more variable change in ventilation in the individual infants during AS. There was a greater increase in end-tidal PCO2 over the first 60 s during AS (3.3 +/- 0.3 vs. 2.6 +/- 0.2 Torr, in AS and QS, respectively, P less than 0.03). This may indicate a smaller initial increase in alveolar ventilation, relative to CO2 delivery to the lungs, in response to CO2 inhalation during AS. Asynchronous chest wall movements were more common during AS than QS (P less than 0.005) and did not change with CO2. The inconsistent transient ventilatory response to CO2 during AS compared with QS may be important in the behavior of infants to spontaneous episodes of hypercapnia occurring during AS.     

Kinetic studies on partially liganded species of carboxyhemoglobin: alpha 2 CO beta 2 and alpha 2 beta 2CO

The valency hybrids of Hb A, alpha 2CO beta 2+, and alpha 2+ beta 2CO have been prepared by a new high pressure liquid chromatography method, and the kinetics of their CO-combination and dissociation reactions have been studied by double mixing and microperoxidase methods. Both reactions are biphasic. The slow phase in CO-combination and the fast phase in CO-dissociation are due to the reactions of alpha CO2 beta T2 or alpha 2 beta 2CO,T. The fast phase in CO-combination reaction has two components, one due to the dimers of the hybrid and the other due to the R-state tetramer. Immediately after the reduction of the valency hybrids, the overall system is represented by the equation: 2 alpha CO beta in equilibrium alpha 2CO beta 2R in equilibrium alpha 2CO beta 2T or (formula: see text) If the solutions are aged for 3-11 s, the R-state population is reduced gradually to a very small size, and the main species after 11 s of aging are dimers and T-state tetramers. Analysis of the kinetic data indicates slow R in equilibrium T equilibria in the absence of phosphates and significant dissociation of the T-state tetramer. It is concluded that the subunit contacts alpha 1-beta 2 (or alpha 2-beta 1) are impaired seriously in the hybrids. Very slow R in equilibrium T relaxation makes these hybrids unlikely intermediates in the sequential binding of CO to Hb tetramer.     

Interactions between elevated CO2 and N2-fixation determine soybean yield—a test using a non-nodulated mutant

Elevated CO₂ increases seed production more in plant species that form a symbiotic association with N₂–fixing bacteria than in species without such association. We studied the mechanism of the increase of seed production with elevated CO₂ using nodulated soybean (Glycine max cv. Enrei) and its non-nodulated isogenic line (cv. En1282). Increase in seed production with elevated CO₂ was observed in nodulated Enrei but was not in non-nodulated En1282. The increase in seed production in Enrei was explained by the increase in the rate of dry mass production during the reproductive period. This increase was associated with the increase in N assimilation in the reproductive period and the seed N concentration that remained the same as that at ambient CO₂. Dry mass production and nitrogen assimilation did not increase in the vegetative phase in both lines. These results accorded with the amount of nodules in Enrei that increased at elevated CO₂ especially after flowering. We conclude that the increase in N assimilation in the reproductive period would be the key for increasing soybean yield in the future high-CO₂ world.     

Double-mixing kinetic studies of the reactions of methyl isocyanide and CO with diliganded intermediates of hemoglobin: alpha 2CO beta 2 and alpha 2 beta 2CO

Kinetics of the reactions of CO and methyl isocyanide with two diliganded intermediates of hemoglobin, alpha 2CO beta 2 and alpha 2 beta 2CO, have been studied by double-mixing and microperoxidase methods. The valency hybrids were prepared by high-pressure liquid chromatography. The reaction time courses of ligand combination and dissociation with both of the ligands were biphasic, and in CO combination reaction the zero-time amplitudes of the two phases were independent of the protein concentration. In the presence of 2 M urea the reaction time course was clearly dependent on protein concentration, as the zero-time amplitude of the fast phase increased at lower protein concentrations. These two observations indicate that little dissociation of tetramers into dimers occurs in the absence of urea. Consistent with this, the kinetic data for the reactions of CO best fit a reaction model consisting of two tetrameric species not in rapid equilibrium with each other. Various considerations, however, suggest that the reaction model is more appropriately described as 2D in equilibrium R in equilibrium T. The reaction of triliganded species (Hb4(CO)2Me1) with methyl isocyanide was monophasic, and the reaction model suggested a fast T in equilibrium R structural change after the binding of the third ligand. Although the precise structural nature of the two species remains undefined, it is concluded that the biphasicity in the reactions of the two hybrids is characteristic of the diliganded species only and is independent of the nature of the ligand.