桉树叶片光合色素含量高光谱估算模型

色素在植物的生理生态过程中非常重要,利用高光谱数据,揭示光谱反射率上特征波段与光合色素含量间的关系将有助于理解光合色素光谱反射特征的规律,同时为利用高光谱遥感技术快速无损监测植物叶片光合色素提供了技术支持.利用野外采集的桉树叶片样本,在实验室内测定了叶片的高光谱反射率及对应的叶绿素、类胡萝卜素含量.利用光谱分析技术和统计学方法对光谱数据进行处理分析,提取了光谱特征参量,并建立叶绿素、类胡萝卜素含量与光谱特征参量间的估算模型.通过精度检验,研究结果表明以(SDr-SDb)/(SDr+SDb)为变量建立的指数模型估算效果最佳.     

Photon echo studies of photosynthetic light harvesting

The broad linewidths in absorption spectra of photosynthetic complexes obscure information related to their structure and function. Photon echo techniques represent a powerful class of time-resolved electronic spectroscopy that allow researchers to probe the interactions normally hidden under broad linewidths with sufficient time resolution to follow the fastest energy transfer events in light harvesting. Here, we outline the technical approach and applications of two types of photon echo experiments: the photon echo peak shift and two-dimensional (2D) Fourier transform photon echo spectroscopy. We review several extensions of these techniques to photosynthetic complexes. Photon echo peak shift spectroscopy can be used to determine the strength of coupling between a pigment and its surrounding environment including neighboring pigments and to quantify timescales of energy transfer. Two-dimensional spectroscopy yields a frequency-resolved map of absorption and emission processes, allowing coupling interactions and energy transfer pathways to be viewed directly. Furthermore, 2D spectroscopy reveals structural information such as the relative orientations of coupled transitions. Both classes of experiments can be used to probe the quantum mechanical nature of photosynthetic light-harvesting: peak shift experiments allow quantification of correlated energetic fluctuations between pigments, while 2D techniques measure quantum beating directly, both of which indicate the extent of quantum coherence over multiple pigment sites in the protein complex. The mechanistic and structural information obtained by these techniques reveals valuable insights into the design principles of photosynthetic light-harvesting complexes, and a multitude of variations on the methods outlined here.     

Spectroscopy of individual light-harvesting 2 complexes of Rhodopseudomonas acidophila: diagonal disorder, intercomplex heterogeneity, spectral diffusion, and energy transfer in the B800 band

This paper reports a detailed spectroscopic study of the B800 absorption band of individual light-harvesting 2 (LH2) complexes of the photosynthetic purple bacterium Rhodopseudomonas acidophila at 1. 2 K. By applying single-molecule detection techniques to this system, details and properties can be revealed that remain obscured in conventional ensemble experiments. For instance, from fluorescence-excitation spectra of the individual complexes a more direct measure of the diagonal disorder could be obtained. Further spectral diffusion phenomena and homogeneous linewidths of individual bacteriochlorophyll a (BChl a) molecules are observed, revealing valuable information on excited-state dynamics. This work demonstrates that it is possible to obtain detailed spectral information on individual pigment-protein complexes, providing direct insight into their electronic structure and into the mechanisms underlying the highly efficient energy transfer processes in these systems.     

P515的测量原理、方法和应用

光谱技术已广泛应用于光合研究领域,如光吸收信号P515和P700氧化还原动力学以及叶绿素荧光等,可快速、准确地检测植物的光合活性。P515信号广泛存在于高等植物和藻类中,是类囊体膜上的色素分子吸收光能后,其吸收光谱发生位移造成。利用光诱导的P515快速和慢速动力学,可检测PSI和PSII反应中心的比值、ATP合酶的质子...     

Photoacclimation and the effect of the symbiotic environment on the photosynthetic response of symbiotic dinoflagellates in the tropical marine hydroid Myrionema amboinense

Symbiotic dinoflagellates of the genus Symbiodinium and residing in the tropical hydroid Myrionema amboinense acclimate to low photon flux associated with low light 'shade' environments by increasing the amount of photosynthetic pigments per algal cell. The photosynthetic light intensity (PI) curves suggested that the low-light pigment response involved an increase in the number of photosynthetic units (PSU) in the chloroplast in addition to any increases in PSU size. Comparisons of light-dependent portion of the P-I curves of freshly isolated zooxanthellae (FIZ) with those from symbionts within the intact animal suggest that the host cell environment reduced average light levels reaching the symbiotic algae by more than half. This phenomenon may protect the algae from photobleaching of pigments and/or photoinhibition of photosynthesis at high light intensities present in shallow water habitats. In addition, maximum photosynthesis (P(max)) of symbionts removed from the host cell was higher than that recorded from dinoflagellates in the intact association, suggesting that the availability of carbon dioxide for photosynthesis may be limited in the intact hydroid. Shaded polyps contained fewer zooxanthellae and had less tissue biomass (measured as protein) than unshaded polyps. However symbionts from shaded polyps acclimated to the low light intensities by increasing chlorophyll levels and photosynthetic rates. The higher photosynthetic rates may have resulted from increased availability of carbon dioxide associated with lower symbiont density. Calculations of the contribution of zooxanthellae carbon to the host animal's respiratory demand (CZAR) showed that zooxanthellae from shaded polyps living in the field potentially provide about the same amount of carbon to their host as zooxanthellae from polyps living in the field in unshaded high light intensities.     

Do all chlorophyll fluorescence emission wavelengths capture the spring recovery of photosynthesis in boreal evergreen foliage?

Chlorophyll a fluorescence (ChlF) is closely related to photosynthesis and can be measured remotely using multiple spectral features as solar‐induced fluorescence (SIF). In boreal regions, SIF shows particular promise as an indicator of photosynthesis, in part because of the limited variation of seasonal light absorption in these ecosystems. Seasonal spectral changes in ChlF could yield new information on processes such as sustained nonphotochemical quenching (NPQ_S) but also disrupt the relationship between SIF and photosynthesis. We followed ChlF and functional and biochemical properties of Pinus sylvestris needles during the photosynthetic spring recovery period to answer the following: (a) How ChlF spectra change over seasonal timescales? (b) How pigments, NPQ_S, and total photosynthetically active radiation (PAR) absorption drive changes of ChlF spectra? (c) Do all ChlF wavelengths track photosynthetic seasonality? We found seasonal ChlF variation in the red and far‐red wavelengths, which was strongly correlated with NPQ_S, carotenoid content, and photosynthesis (enhanced in the red), but not with PAR absorption. Furthermore, a rapid decrease in red/far‐red ChlF ratio occurred in response to a cold spell, potentially relating to the structural reorganization of the photosystems. We conclude that all current SIF retrieval features can track seasonal photosynthetic dynamics in boreal evergreens, but the full SIF spectra provides additional insight.     

First solid-state NMR analysis of uniformly ¹³C-enriched major light-harvesting complexes from Chlamydomonas reinhardtii and identification of protein and cofactor spin clusters

The light-harvesting complex II (LHCII) is the main component of the antenna system of plants and green algae and plays a major role in the capture of sun light for photosynthesis. The LHCII complexes have also been proposed to play a key role in the optimization of photosynthetic efficiency through the process of state 1-state 2 transitions and are involved in down-regulation of photosynthesis under excess light by energy dissipation through non-photochemical quenching (NPQ). We present here the first solid-state magic-angle spinning (MAS) NMR data of the major light-harvesting complex (LHCII) of Chlamydomonas reinhardtii, a eukaryotic green alga. We are able to identify nuclear spin clusters of the protein and of its associated chlorophyll pigments in 13C-13C dipolar homonuclear correlation spectra on a uniformly 13C-labeled sample. In particular, we were able to resolve several chlorophyll 131 carbon resonances that are sensitive to hydrogen bonding to the 131-keto carbonyl group. The data show that 13C NMR signals of the pigments and protein sites are well resolved, thus paving the way to study possible structural reorganization processes involved in light-harvesting regulation through MAS solid-state NMR.     

Bio-optical modeling of photosynthetic pigments in corals

The spectral reflectance of coral is inherently related to the amounts of photosynthetic pigments present in the zooxanthellae. There are no studies, however, showing that the suite of major photosynthetic pigments can be predicted from optical reflectance spectra. In this study, we measured cm-scale in vivo and in situ spectral reflectance for several colonies of the massive corals Porites lobata and Porites lutea, two colonies of the branching coral Porites compressa, and one colony of the encrusting coral Montipora flabellata in Kaneohe Bay, Oahu, Hawaii. For each reflectance spectrum, we collected a tissue sample and utilized high-performance liquid chromatography to quantify six major photosynthetic pigments, located in the zooxanthellae. We used multivariate multiple regression analysis with cross-validation to build and test an empirical linear model for predicting pigment concentrations from optical reflectance spectra. The model accurately predicted concentrations of chlorophyll a, chlorophyll c ₂, peridinin, diadinoxanthin, diatoxanthin and β-carotene, with correlation coefficients of 0.997, 0.941, 0.995, 0.996, 0.980 and 0.984, respectively. The relationship between predicted and actual concentrations was 1:1 for each pigment, except chlorophyll c ₂. This simple empirical model demonstrates the potential for routine, rapid, non-invasive monitoring of coral-zooxanthellae status, and ultimately for remote sensing of reef biogeochemical processes.     

Assessing photosynthetic downregulation in sunflower stands with an optically-based model

Using a simple light-use efficiency model based on optical measurements, we explored spatial patterns of photosynthetic activity in fertilized and unfertilized sunflower stands. The model had two components: (1) absorbed photosynthetically active radiation (APAR), and (2) radiation-use efficiency. APAR was the product of photosynthetic photon flux density (PPFD) and leaf absorptance, which was derived from leaf reflectance. Radiation-use efficiency was either assumed to be constant or allowed to vary linearly with the photochemical reflectance index (PRI), a measure of xanthophyll cycle pigment activity. When efficiency was assumed to be constant, the model overestimated photosynthetic rates in upper canopy layers exposed to direct PPFD, particularly in the unfertilized canopy due to the greater photosynthetic downregulation associated with higher levels of photoprotective (de-epoxidized) xanthophyll cycle pigments in these conditions. When efficiency was allowed to vary according to the PRI, modeled photosynthetic rates closely matched measured rates for all canopy layers in both treatments. These results illustrate the importance of considering reduced radiation-use efficiency due to photosynthetic downregulation when modeling photosynthesis from reflectance, and illustrate the potential for detecting radiation-use efficiency through leaf optical properties. At least under the conditions of this study, these results also suggest that xanthophyll cycle pigment activity and net carbon uptake are coordinately regulated, allowing assays of Photosystem II activity to reveal changing rates of net assimilation. Because the optical methods in this study are adaptable to multiple spatial scales (leaf to landscape), this approach may provide a scalable model for estimating photosynthetic rates independently from flux measurements.This revised version was published online in October 2005 with corrections to the Cover Date.     

Elucidation of structure-function relationships in photosynthetic light-harvesting antenna complexes by non-linear polarization spectroscopy in the frequency domain (NLPF)

Photosynthetically active pigments are usually organized into pigment-protein complexes. These include light-harvesting antenna complexes (LHCs) and reaction centers. Site energies of the bound pigments are determined by interactions with their environment, i.e., by pigment-protein as well as pigment-pigment interactions. Thus, resolution of spectral substructures of the pigment-protein complexes may provide valuable insight into structure-function relationships. By means of conventional (linear) and time-resolved spectroscopic techniques, however, it is often difficult to resolve the spectral substructures of complex pigment-protein assemblies. Nonlinear polarization spectroscopy in the frequency domain (NLPF) is shown to be a valuable technique in this regard. Based on initial experimental work with purple bacterial antenna complexes as well as model systems NLPF has been extended to analyse the substructure(s) of very complex spectra, including analyses of interactions between chlorophylls and "optically dark" states of carotenoids in LHCs. The paper reviews previous work and outlines perspectives regarding the application of NLPF spectroscopy to disentangle structure-function relationships in pigment-protein complexes.     

Electronic excited states and excitation transfer kinetics in the Fenna-Matthews-Olson protein of the photosynthetic bacterium Prosthecochloris aestuarii at low temperatures

The molecular structure-function relationship of the Fenna-Matthews-Olson light-harvesting complex of the photosynthetic green bacterium Prosthecochloris aestuarii has been investigated. It has been assumed that the electronic excited states responsible for the function (transfer of electronic excitation energy) result from the dipole-dipole interactions between the bacteriochlorophyll molecules bound to the polypeptide chain of the complex at a specific three-dimensional geometry. The molecular structure-electronic excited states relationship has been addressed on the basis of simultaneous simulations of several spectroscopic observations. Current electronic excited state models for the Fenna-Matthews-Olson complex have generally been based on obtaining an optimal match between the information contents of the optical steady-state spectra and the bacteriochlorophyll organization. Recent kinetic and spectral information gathered from ultrafast time-resolved measurements have not yet been used effectively for further refinement of the excited state models and for quantification of the relation between the excited states and the energy transfer processes. In this study, we have searched for a model that not only can explain the key features of several steady-state spectra but also the temporal and spectral evolution observed in a recent absorption difference experiment and we have discussed the implications of this model for equilibration of the electronic excitation energy in systems at low temperatures. Received: 12 June 1998 / Revised version: 19 October 1998 / Accepted: 30 November 1998     

Modeling chlorophyll a fluorescence transient: Relation to photosynthesis

To honor Academician Alexander Abramovitch Krasnovsky, we present here an educational review on the relation of chlorophyll a fluorescence transient to various processes in photosynthesis. The initial event in oxygenic photosynthesis is light absorption by chlorophylls (Chls), carotenoids, and, in some cases, phycobilins; these pigments form the antenna. Most of the energy is transferred to reaction centers where it is used for charge separation. The small part of energy that is not used in photochemistry is dissipated as heat or re-emitted as fluorescence. When a photosynthetic sample is transferred from dark to light, Chl a fluorescence (ChlF) intensity shows characteristic changes in time called fluorescence transient, the OJIPSMT transient, where O (the origin) is for the first measured minimum fluorescence level; J and I for intermediate inflections; P for peak; S for semi-steady state level; M for maximum; and T for terminal steady state level. This transient is a real signature of photosynthesis, since diverse events can be related to it, such as: changes in redox states of components of the linear electron transport flow, involvement of alternative electron routes, the build-up of a transmembrane pH gradient and membrane potential, activation of different nonphotochemical quenching processes, activation of the Calvin-Benson cycle, and other processes. In this review, we present our views on how different segments of the OJIPSMT transient are influenced by various photosynthetic processes, and discuss a number of studies involving mathematical modeling and simulation of the ChlF transient. A special emphasis is given to the slower PSMT phase, for which many studies have been recently published, but they are less known than on the faster OJIP phase.     

Sun‐induced fluorescence – a new probe of photosynthesis: First maps from the imaging spectrometer HyPlant

Variations in photosynthesis still cause substantial uncertainties in predicting photosynthetic CO₂ uptake rates and monitoring plant stress. Changes in actual photosynthesis that are not related to greenness of vegetation are difficult to measure by reflectance based optical remote sensing techniques. Several activities are underway to evaluate the sun‐induced fluorescence signal on the ground and on a coarse spatial scale using space‐borne imaging spectrometers. Intermediate‐scale observations using airborne‐based imaging spectroscopy, which are critical to bridge the existing gap between small‐scale field studies and global observations, are still insufficient. Here we present the first validated maps of sun‐induced fluorescence in that critical, intermediate spatial resolution, employing the novel airborne imaging spectrometer HyPlant. HyPlant has an unprecedented spectral resolution, which allows for the first time quantifying sun‐induced fluorescence fluxes in physical units according to the Fraunhofer Line Depth Principle that exploits solar and atmospheric absorption bands. Maps of sun‐induced fluorescence show a large spatial variability between different vegetation types, which complement classical remote sensing approaches. Different crop types largely differ in emitting fluorescence that additionally changes within the seasonal cycle and thus may be related to the seasonal activation and deactivation of the photosynthetic machinery. We argue that sun‐induced fluorescence emission is related to two processes: (i) the total absorbed radiation by photosynthetically active chlorophyll; and (ii) the functional status of actual photosynthesis and vegetation stress.     

Photosynthesis, Growth, and Ultraviolet Irradiance Absorbance of Cucurbita pepo L. Leaves Exposed to Ultraviolet-B Radiation (280-315 nm)

Net photosynthesis, growth, and ultraviolet (UV) radiation absorbance were determined for the first leaf of Cucurbita pepo L. exposed to two levels of UV-B irradiation and a UV-B radiation-free control treatment. Absorbance by extracted flavonoid pigments and other UV-B radiation-absorbing compounds from the first leaves increased with time and level of UV-B radiation impinging on leaf surfaces. Although absorbance of UV-B radiation by extracted pigments increased substantially, UV-B radiation attenuation apparently was insufficient to protect completely the photosynthetic apparatus or leaf growth processes. Leaf expansion was repressed by daily exposure to 1365 Joules per meter per day of biologically effective UV-B radiation but not by exposure to 660 Joules per meter per day. Photosynthesis measured through ontogenesis of the first leaf was depressed by both UV-B radiation treatments. Repression of photosynthesis by UV-B radiation was especially evident during the ontogenetic period of maximum photosynthetic activity.     

Model of aggregation of pigments in the chlorosomal antenna of the green bacteria Chloroflexus aurantiacus

Independent experimental and theoretical evaluation was performed for the adequacy of our previously proposed general molecular model of structural organization of light-harvesting pigments in chlorosomal bacteriochlorophyll (BChl) c/d/e-containing superantenna of different green bacteria. Simultaneous measurement of hole burning in the optical spectra of chlorosomal BChl c and temperature dependence of steady-state fluorescence spectra of BChl c was accomplished in intact cells of photosynthetic green bacterium Chloroflexus aurantiacus; this allows unambiguous determination of the structure of exciton levels of BChl c oligomers in this natural antenna, which is a fundamental criterion for adequacy of any molecular model for in vivo aggregation of antenna pigments. Experimental data were shown to confirm our model of organization of oligometric pigments in chlorosomal BChl c antenna of green bacterium Chloroflexus aurantiacus. This model, which is based on experimental data and our theory of spectroscopy of oligomeric pigments, implies that the unit building block of BChl c antenna is a cylindrical assembly containing six excitonically coupled linear pigment chains whose exciton structure with intense upper levels provides for the optimal spectral properties of the light-harvesting antenna.     

Insights into the mechanisms and dynamics of energy transfer in plant light-harvesting complexes from two-dimensional electronic spectroscopy

During the past two decades, two-dimensional electronic spectroscopy (2DES) and related techniques have emerged as a potent experimental toolset to study the ultrafast elementary steps of photosynthesis. Apart from the highly engaging albeit controversial analysis of the role of quantum coherences in the photosynthetic processes, 2DES has been applied to resolve the dynamics and pathways of energy and electron transport in various light-harvesting antenna systems and reaction centres, providing unsurpassed level of detail. In this paper we discuss the main technical approaches and their applicability for solving specific problems in photosynthesis. We then recount applications of 2DES to study the exciton dynamics in plant and photosynthetic light-harvesting complexes, especially light-harvesting complex II (LHCII) and the fucoxanthin-chlorophyll proteins of diatoms, with emphasis on the types of unique information about such systems that 2DES is capable to deliver. This article is part of a Special Issue entitled Light harvesting, edited by Dr. Roberta Croce.     

Cellular perspectives for improving mesophyll conductance

After entering the leaf, CO₂ faces an intricate pathway to the site of photosynthetic fixation embedded within the chloroplasts. The efficiency of CO₂ flux is hindered by a number of structural and biochemical barriers which, together, define the ease of flow of the gas within the leaf, termed mesophyll conductance. Previous authors have identified the key elements of this pathway, raising the prospect of engineering the system to improve CO₂ flux and, thus, to increase leaf photosynthetic efficiency. In this review, we provide a perspective on the potential for improving the individual elements that contribute to this complex parameter. We lay particular emphasis on generation of the cellular architecture of the leaf which sets the initial boundaries of a number of mesophyll conductance parameters, incorporating an overview of the molecular transport processes which have been proposed as major facilitators of CO₂ flux across structural boundaries along the pathway. The review highlights the research areas where future effort might be invested to increase our fundamental understanding of mesophyll conductance and leaf function and, consequently, to enable translation of these findings to improve the efficiency of crop photosynthesis.     

植物叶片花青素的光破坏防御机制研究进展

植物花青素广泛分布在植物的根、茎、叶、花和果实等器官中,是植物形态建成过程中或响应逆境而产生的一种次生代谢物质.植物叶片中的花青素具有特殊的化学结构和光谱特性,在光破坏防御机制方面发挥了重要的作用,已经成为植物光合生理生态的研究热点.本文综述了近年来植物叶片花青素与光合作用的研究进展,从叶片花青素的分布、光谱特性及其与光合色素的关系等方面说明花青素对植物光合作用的影响,重点介绍了叶片花青素通过光吸收、抗氧化剂和渗透调节等在植物光破坏防御机制方面的作用,展望了今后的主要研究方向