适用于植物光合作用的光声池设计研究进展

光声光谱检测可很好地应用在植物光合作用的研究领域,可更有效于传统检测方法并已在大量检测研究中得以证明。在一套光声光谱仪检测装置中,光声池是其核心部件,其设计好坏直接影响着实验的结果。文章阐述了适用于植物光合作用的光声池的设计方法及其需要关注的关键问题;展望了植物光合作用的光声光谱检测与其他检测方法联用的重点及其研究方向;提出了光声池设计中应着重关注其活体实时在线检测及其相关技术问题。     

Synthetic data framework to estimate the minimum detectable concentration of contrast agents for multispectral optoacoustic imaging of small animals

The concentrations of contrast agents for optoacoustic imaging of small animals must usually be optimized through extensive pilot experiments on a case‐by‐case basis. The present work describes a streamlined approach for determining the minimum detectable concentration (MDC) of a contrast agent given experimental conditions and imaging system parameters. The developed Synthetic Data Framework (SDF) allows estimation of MDCs of various contrast agents under different tissue conditions without extensive animal experiments. The SDF combines simulated optoacoustic signals from exogenously administered contrast agents with in vivo experimental signals from background tissue to generate realistic synthetic multispectral optoacoustic images. In this paper, the SDF is validated with in vivo measurements and demonstrates close agreement between SDF synthetic data and experimental data in terms of both image intensity and MDCs. Use of the SDF to estimate MDCs for fluorescent dyes and nanoparticles at different tissue depths and for imaging lesions of different sizes is illustrated.     

Isotropic high resolution optoacoustic imaging with linear detector arrays in bi‐directional scanning

Optoacoustic (photoacoustic) imaging is often performed with one‐dimensional transducer arrays, in analogy to ultrasound imaging. Optoacoustic imaging using linear arrays offers ease of implementation but comes with several performance drawbacks, in particular poor elevation resolution, i.e. the resolution along the axis perpendicular to the focal plane. Herein, we introduce and investigate a bi‐directional scanning approach using linear arrays that can improve the imaging performance to quasi‐isotropic transverse resolution. We study the approach theoretically and perform numerical simulations and phantom measurements to evaluate its performance under defined conditions. Finally, we discuss the features and the limitations of the proposed method.

The poor elevation resolution in a linear scan (left image) is overcome by the proposed bi‐directional scanning approach that yields isotropic transverse resolution (right).     

On the nature of the photosynthetic energy storage monitored by photoacoustic spectroscopy

The photosynthetic energy storage yield of uncoupled thylakoid membranes was monitored by photoacoustic spectroscopy at various measuring beam intensities. The energy storage rate as evaluated by the half-saturation measuring beam intensity (i₅₀) was inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea, by heat inactivation or by artificial electron acceptors specific for photosystem I or photosystem II; and was activated by electron donors to photosystem I. The reactions involving both photosystems were all characterized by a similar maximal energy storage yield of 16±2 percent. The data could be interpreted if we assumed that the energy storage elicited by the photosystems at 35 Hz is detected at the level of the plastoquinone pool.Abbreviations PS photosystem - Tes N-Tris [hydroxymethl] methyl-2-aminoethanesulfonic acid - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCIP 2,6-dichlorophenolindophenol - FeCN potassium ferricyanide - DCBQ 2,5-dichlorobenzoquinone - TMPD N,N,N-tetramethyl-p-phenilenediamine     

Nonlinear optoacoustic readings from diffusive media at near‐infrared wavelengths

Optoacoustic (photoacoustic) imaging assumes that the detected signal varies linearly with laser energy. However, nonlinear intensity responses as a function of light fluence have been suggested in optoacoustic microscopy, that is, within the first millimeter of tissue. In this study, we explore the presence of nonlinearity deeper in tissue (~4 mm), as it relates to optoacoustic mesoscopy, and investigate the fluence required to delineate a switch from linear to nonlinear behavior. Optoacoustic signal nonlinearity is studied for different materials, different wavelengths and as a function of changes in the scattering and absorption coefficient of the medium imaged. We observe fluence thresholds in the mJ/cm² range and preliminary find that different materials may exhibit different nonlinearity patterns. We discuss the implications of nonlinearity in relation to image accuracy and quantification in optoacoustic tomography.      

Photoacoustic Spectroscopy and its Application in Plant Science

The principles of photoacoustic spectroscopy are outlined. This new and still developing technique enables one to detect non-radiative de-excitation processes. It is possible to distinguish between signals emenating from different depths of the sample. In plant science photoacoustic spectroscopy has mainly been applied in photosynthesis research. Here it allows the detection of gross oxygen evolution and gives information about the energy balance of the primary photosynthetic reaction.     

Femtosecond nuclear oscillations under charge separation in reaction centers of photosynthesis

Results are presented of a study of primary processes of formation of the charge separated states P⁺B_A ^- and P⁺H_A ^- (where P is the primary electron donor, B_A and H_A the primary and secondary electron acceptors) in native and pheophytin-modified reaction centers (RCs) of Rhodobacter sphaeroides R-26 by methods of femtosecond spectroscopy of absorption changes at low temperature. Coherent oscillations were studied in the kinetics at 935 nm (P* stimulated emission band), at 1020 nm (B_A ^- absorption band), and at 760 nm (H_A absorption band). It was found that when the wavepacket created under femtosecond light excitation approaches the intersection between P* and P⁺B_A ^- potential surfaces at 120- and 380-fsec delays, the formation of two electron states emitting light at 935 nm (P*) and absorbing light at 1020 nm (P⁺B_A ^-) takes place. At the later time the wavepacket motion has a frequency of 32 cm^-1 and is accompanied by electron transfer from P* to B_A in pheophytin-modified and native RCs and further to H_A in native RCs. It was shown that electron transfer processes monitored by the 1020-nm absorption band development as well as by bleaching of 760-nm absorption band have the enhanced 32 cm^-1 mode in the Fourier transform spectra.     

Reaction center and antenna processes in photosynthesis at low temperature

Around 1960 experiments of Arnold and Clayton, Chance and Nishimura and Calvin and coworkers demonstrated that the primary photosynthetic electron transfer processes are not abolished by cooling to cryogenic temperatures. After a brief historical introduction, this review discusses some aspects of electron transfer in bacterial reaction centers and of optical spectroscopy of photosynthetic systems with emphasis on low-temperature experiments.Abbreviations (B)Chl (bacterio)chlorophyll - (B)Phe (bacterio)pheophytin - FMO Fenna-Matthews-Olson - LH1, LH2 light harvesting complexes of purple bacteria - LHC II, CP47 light harvesting complexes of Photosystem II - P, P870 primary electron donor - RC reaction center     

Characterization of drought resistance in a wild relative of wheat,Triticum kotschyi

Wild relatives of wheat have served as a genetic source for economically useful traits. A better understanding of the mechanisms underlying such traits may be useful in the genetic transfer and selection processes. Research was undertaken to compare the effects of controlled water stress on photosynthetic parameters in Triticum kotschyi, a drought resistant wild wheat and Triticum aestivum cv. Lakhish, a drought sensitive wheat cultivar. During stress development, the leaf water potential decreased at a slower rate, and the quantum yield of oxygen evolution, measured photoacoustically in vivo, decreased to a smaller extent in the drought resistant wild wheat than in the wheat cultivar. The decrease in quantum yield at water potentials from –0.9 Mpa down to –2.3 Mpa was not accompanied by damage to PS II reaction centers as there was no change in variable fluorescence. Below –2.3 Mpa the fluorescence yield of both species decreased indicating loss of intrinsic efficiency of PS II. The osmotic potential of cell sap was found to decrease at the same rate in both species at high hydration states. Proline accumulated to a much greater extent in the wild wheat as compared to the cultivated wheat as a result of water stress. Drought resistance was also examined in relation to thylakoid membrane fluidity measured by fluorescence polarization. Thylakoid membrane fluidity was fully maintained in the wild wheat, but decreased substantially in the wheat cultivar, at equal tissue water potentials below –1.9 Mpa. One mechanism for maintaining the higher quantum yield of oxygen evolution during severe stress (at water potentials below –1.9 Mpa), may involve the greater stability of thylakoid membrane fluidity in the wild wheat.Abbreviations DPH 1,6-diphenyl-1,3,5-hexatriene - LHC II light-harvesting chlorophyll-protein a/b complex - LWP leaf water potential - PS I, PS II Photosystem I, II - RUBPcase ribulose 1,5-bisphosphate carboxylase     

Three‐dimensional multispectral optoacoustic mesoscopy reveals melanin and blood oxygenation in human skin in vivo

Optical imaging plays a major role in disease detection in dermatology. However, current optical methods are limited by lack of three‐dimensional detection of pathophysiological parameters within skin. It was recently shown that single‐wavelength optoacoustic (photoacoustic) mesoscopy resolves skin morphology, i.e. melanin and blood vessels within epidermis and dermis. In this work we employed illumination at multiple wavelengths for enabling three‐dimensional multispectral optoacoustic mesoscopy (MSOM) of natural chromophores in human skin in vivo operating at 15–125 MHz. We employ a per‐pulse tunable laser to inherently co‐register spectral datasets, and reveal previously undisclosed insights of melanin, and blood oxygenation in human skin. We further reveal broadband absorption spectra of specific skin compartments. We discuss the potential of MSOM for label‐free visualization of physiological biomarkers in skin in vivo.

Cross‐sectional optoacoustic image of human skin in vivo. The epidermal layer is characterized by melanin absorption. A vascular network runs through the dermal layer, exhibiting blood oxygenation values of 50–90%. All scale bars: 250 µm     

循环光合磷酸化和光合作用

光合作用被称为"地球上最重要的化学反应",其二氧化碳同化是由还原辅酶II(NADPH)和腺三磷(ATP)来推动的。ATP主要来源于非循环光合磷酸化和循环光合磷酸化,但以往研究集中在前者。21世纪以来,随着测定技术的发展和多条与循环光合磷酸化有关的电子传递途径的发现,循环光合磷酸化的重要性和功能引起了极大地关注。该文作者结合自己实验室的相关的研究,围绕循环光合磷酸化的发现和重要性、同化力两个组分的比例与促进光合磷酸化提高光合作用的途径进行探讨,为进一步深入研究提供参考。     

Formation of stromatolite lamina at the interface of oxygenic–anoxygenic photosynthesis

In modern stromatolites, mineralization results from a complex interplay between microbial metabolisms, the organic matrix, and environmental parameters. Here, we combined biogeochemical, mineralogical, and microscopic analyses with measurements of metabolic activity to characterize the mineralization processes and products in an emergent (<18 months) hypersaline microbial mat. While the nucleation of Mg silicates is ubiquitous in the mat, the initial formation of a Ca‐Mg carbonate lamina depends on (i) the creation of a high‐pH interface combined with a major change in properties of the exopolymeric substances at the interface of the oxygenic and anoxygenic photoautotrophic layers and (ii) the synergy between two major players of sulfur cycle, purple sulfur bacteria, and sulfate‐reducing bacteria. The repetition of this process over time combined with upward growth of the mat is a possible pathway leading to the formation of a stromatolite.     

An automatic system to study the responses of respiration and photosynthesis by submerged macrophytes to environmental variables

An apparatus to measure the rates of respiration and photosynthesis of aquatic plants in water at velocities of up to 200 mm s^–1 in a closed water-flow system with partial recirculation, is described. The temperature, the light regime and the concentration of dissolved oxygen are controlled automatically. Typical results are given for Ranunculus penicillatus var. calcareus which were repeatable between the same season in different years and compared with published data.     

Enabling in vivo measurements of nanoparticle concentrations with three‐dimensional optoacoustic tomography

In this report, we demonstrate the feasibility of using optoacoustic tomography (OAT) to evaluate biodistributions of nanoparticles in animal models. The redistribution of single‐walled carbon nanotubes (SWCNTs) was visualized in living mice. Nanoparticle concentrations in harvested organs were measured spectroscopically using the intrinsic optical absorption and fluorescence of SWCNTs. Observed increases in optoacoustic signal brightness in tissues were compared with increases in optical absorption coefficients caused by SWCNT accumulation. The methodology presented in this report can further be extended to calibrate the sensitivity of an optoacoustic imaging system for a range of changes in optical absorption coefficient values at specific locations or organs in a mouse body to enable noninvasive measurements of nanoparticle concentrations in vivo. Additionally, qualitative information provided by OAT and quantitative information obtained ex vivo may provide valuable feedback for advancing methods of quantitative analysis with OAT. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

施肥结构对茶树（Camellia sinensis (L.) Kuntze）光合作用及其生态生理因子日变化的影响

以福云早毫品种为材料,在新开茶园连续5a进行了7种施肥结构的大田对比试验,研究了茶树净光合速率(Pn)、生态生理因子的日变化及施肥结构对它们的影响,结果表明:茶树晴天Pn的日变化呈典型的双峰曲线,有明显的"午休"现象,且受生态生理因子的影响,光合有效辐射、气温和空气CO:浓度是茶园生态系统的主导因子,蒸腾速率、气孔导度和胞间CO2浓度是生理主导因子,进一步进行回归和通径分析发现,生态因子特别是光温因子对Pn的影响最大.施肥结构对茶树的光合有效辐射、叶面温度、空气温度和湿度等相对稳定的气候因子影响不大,但与纯施化肥、间作白三叶草 不施肥和完全不施肥相比,100%、75%、50%和25%施用有机肥4种处理明显增加了蒸腾速率和气孔导度,显著提高了日净光合速率,吸收和消耗了更多的CO2.以Pn和其他8个主要生态生理因子为指标进行聚类分析,7种施肥结构茶树光合作用系统分为100%和75%施用有机肥、50%和25%施用有机肥、纯施化肥和间作白三叶草 不施肥、完全不施肥4类,其中100%和75%施用有机肥的效果最好.     

The recovery of photosynthesis in tomato subsequent to chilling exposure

The overall success of a plant in coping with low temperature sensitivity of photosynthesis is dependent not only on the maximum extent of inhibition suffered for a given time of low temperature exposure but also on the persistence of the inhibition after normal growth temperatures are restored. Thus the capacity of recovery and the speed with which a plant can recover from the effects of chilling exposure are important parameters in determining how devastating the chilling event will be on season-long growth and yields. We have studied the recovery of CO₂-saturated photosynthesis from the injury caused by exposing intact tomato plants (Lycopersicon esculentum Mill. cv. Floramerica) or detached tomato leaves to a temperature of 1°C in the dark for varying periods of time. We found that net photosynthesis was fully recovered within 12 h after returning the plants to 25°C in the dark, even after chilling exposures as long as 45 h. This was true for intact plants as well as for detached leaves that were supplied with water. When chilling took place in the light (4°C, 1000 E · m^-2 · s^-1, PAR) inhibition of photosynthesis was more severe and appeared more quickly and the recovery was slower and incomplete. A 12 h chilling exposure in the light resulted in injury to net photosynthesis that was not fully recovered even after 50 h. Chilling damage to photosynthesis developing in the light was distinguished from chilling in the dark by the decreased photosynthetic quantum yield. Not only did high intensity illumination enhance chilling damage of photosynthesis but bright light subsequent to the chilling exposure also delayed the recovery of photosynthesis. At none of the three ambient CO₂ concentrations investigated (300, 1500 and 5000 1.1^-1) did the recovery of photosynthesis depend on stomatal conductance.     

Acclimation to temperature of the response of photosynthesis to increased carbon dioxide concentration in Taraxacum officinale

The relative stimulation of photosynthesis by elevated carbon dioxide in C₃ species normally increases strongly with increasing temperature. This results from the kinetic characteristics of Rubisco, and has potentially important implications for responses of vegetation to increasing atmospheric carbon dioxide. It is often assumed that because Rubisco characteristics are conservative, all C₃ species have the same temperature dependence of the response of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the relative stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 °C. Nevertheless, short-term measurements indicated a strong temperature dependence of the stimulation. This suggested that acclimation to temperature caused the lack of variation in the seasonal data. Experiments in controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 – 25 °C. The apparent specificity of Rubisco for carbon dioxide relative to oxygen at 15 °C, as assayed in vivo by measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied with growth temperature. Changes in the apparent specificity of Rubisco accounted for the acclimation of the temperature dependence of the relative stimulation of photosynthesis by elevated carbon dioxide. It is premature to conclude that low temperatures will necessarily reduce the relative stimulation of photosynthesis caused by rising atmospheric carbon dioxide. This revised version was published online in June 2006 with corrections to the Cover Date.