The impact of high CO2 concentrations on the structure and function of the photosynthetic apparatus and the role of polyamines

Here we examined the influence of high CO2 concentrations on the structure and functioning of the photosynthetic apparatus in the unicellular green alga Scenedesmus obliquus. Presented in this work are: chlorophyll (Chl) a fluorescence induction kinetics, measurements of photosynthetic and respiration rates, estimation of Chl a/Chl b ratios, isolation and quantitative assessment of the photosynthetic subcomplexes, quantitative analyses of thylakoid bound polyamines, and experiments with exogenously supplied polyamines with cultures grown in low- and high-CO2 concentrations. Together, they indicated that high-CO2 concentrations affect polyamines and, more specifically, increase the thylakoid bound putrescine (PUT) level that leads to an increase of the active reaction center density combined with a decrease in the LHCII-size and the ratio of LHCII-oligomeres/LHCII-monomeres. This reorganization of the photosynthetic apparatus leads to enhanced photosynthetic rates, which in combination with the high-CO2 concentrations, leads to an immense increase of biomass (800%). Further incubation for longer time periods under the same conditions produces, due to an increase in cell density, a self-shading effect and photoadaptation of the photosynthetic apparatus to low light conditions and therefore also results in reduction of the high-CO2 effect. The photoadaptation of the photosynthetic apparatus to high-light conditions (Kotzabasis et al. 1999) and the acclimation to high-CO2 concentrations (present work) lead to the same changes in the structure and function of the photosynthetic apparatus. These changes could be induced or inhibited through the manipulation of intracellular polyamines, especially through the putrescine/spermine ratio. The possibility that polyamines influence the photoadaptation of the photosynthetic apparatus and its acclimation to high-CO2 concentrations through a common mechanism is discussed.     

Brassica rapa plants adapted to microgravity with reduced photosystem I and its photochemical activity

The photosynthetic apparatus contains several protein complexes, many of which are regulated by environmental conditions. In this study, the influences of microgravity on PSI and PSII in Brassica rapa plants grown aboard the space shuttle were examined. We found that Brassica plants grown in space had a normal level of growth relative to controls under similar conditions on Earth. Upon return to Earth, cotyledons were harvested and thylakoid membranes were isolated. Analysis of chlorophyll contents showed that the Chl a/b ratio (3.5) in flight cotyledons was much higher than a ratio of 2.42 in the ground controls. The flight samples also had a reduction of PSI complexes and a corresponding 30% decrease of PSI photochemical activity. Immunoblotting showed that the reaction centre polypeptides of PSI were more apparently decreased (e.g. by 24-33% for PsaA and PsaB, and 57% for PsaC) than the light-harvesting complexes. In comparison, the accumulation of PSII complex was less affected in microgravity, thus only a slight reduction in D1, D2 and LHCII was observed in protein blots. However, there was a 32% decrease of OEC1 in the flight samples, indicating a defective OEC subcomplex. In addition, an average 54% increase of the 54 kDa CF1-beta isoform was found in the flight samples, suggesting that space-grown plants suffered from certain stresses, consistent with implications of the increased Chl a/b ratio. Taken together, the results demonstrated that Brassica plants can adapt to spaceflight microgravity, but with significant alterations in chloroplast structures and photosynthetic complexes, and especially reduction of PSI and its activity.     

Low growth temperature-induced changes to pigment composition and photosynthesis in Zea mays genotypes differing in chilling sensitivity

The effects on pigment composition and photosynthesis of low temperature during growth were examined in the third leaf of three chilling-tolerant and three chilling-sensitive genotypes of Zea mays L. The plants were grown under a controlled environment at 24 or 14 °C at a photon flux density (PFD) of 200 or 600 μ mol m^–2 s^–1. At 24 °C, the two classes of genotypes showed little differences in their photosynthetic activity and their composition of pigments. At 14 °C, photosynthetic activity was considerably reduced but the chilling-tolerant genotypes displayed higher photosynthetic rates than the chilling-sensitive ones. Plants grown at 14 °C showed a reduced chlorophyll (Chl) a + b content and a reduced Chl a / b ratio but an increased ratio of total carotenoids to Chl a + b . These changes in pigment composition in plants grown at low temperature were generally more pronounced in the chilling-sensitive genotypes than in the tolerant ones, particularly at high PFD. Furthermore, at 14 °C, all the genotypes showed increased ratios of lutein, neoxanthin and xanthophyll-cycle carotenoids to Chl a + b but a reduced ratio of β -carotene to Chl a + b , especially at high PFD. At 14 °C, the chilling-tolerant genotypes, when compared with the sensitive ones, were characterized by higher contents of β -carotene and neoxanthin, a lower content of xanthophyll-cycle carotenoids, a lower ratio of xanthophylls to β -carotene, and less of their xanthophyll-cycle carotenoid pool in the form of zeaxanthin. These differences between the two classes of genotypes were more pronounced at high PFD than at low PFD. The results are discussed in terms of the relationship that may exist in maize between pigment composition and the capacity to form an efficient photosynthetic apparatus at low growth temperature.     

Membrane system organization in the process of greening of clinorotated barley seedlings

Altered gravity affects on plastid structure and function during greening has not been studied. To elucidate how stimulated microgravity affects pigment apparatus formation in etiolated plants we have been studied clinorotation effects on morphological characteristics and chlorophylls biosynthesis in the first period of greening of barley plant. At the ultrastructural level clinorotation caused alteration of mesophyll cell parameters and organization, destruction of the fine structure of chloroplasts, changes in starch volume and lipid-protein accumulation.     

空间搭载后的蜀葵幼苗叶中光合色素含量及抗氧化酶活性变化

蜀葵种子经返回式卫星搭载后,其幼苗叶中光合色素(叶绿素a、b,胡萝卜素)总量低于地面未经搭载的.叶绿素a b含量明显降低, 叶绿素b的下降幅度远大于叶绿素a,因而Chla/b值增高.经空间搭载后萌发12 d的幼苗体内超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性均低于地面未经搭载的,而丙二醛(MDA)含量则明显升高.     

A reduced model of the fluorescence from the cyanobacterial photosynthetic apparatus designed for the in situ detection of cyanobacteria

Fluorometric determination of the chlorophyll (Chl) content of cyanobacteria is impeded by the unique structure of their photosynthetic apparatus, i.e., the phycobilisomes (PBSs) in the light-harvesting antennae. The problems are caused by the variations in the ratio of the pigment PC to Chl a resulting from adaptation to varying environmental conditions. In order to include cyanobacteria in fluorometric analysis of algae, a simplified energy distribution model describing energy pathways in the cyanobacterial photosynthetic apparatus was conceptualized. Two sets of mathematical equations were derived from this model and tested. Fluorescence of cyanobacteria was measured with a new fluorometer at seven excitation wavelength ranges and at three detection channels (650, 685 and 720 nm) in vivo. By employing a new fit procedure, we were able to correct for variations in the cyanobacterial fluorescence excitation spectra and to account for other phytoplankton signals. The effect of energy-state transitions on the PC fluorescence emission of PBSs was documented. The additional use of the PC fluorescence signal in combination with our recently developed mathematical approach for phytoplankton analysis based on Chl fluorescence spectroscopy allows a more detailed study of cyanobacteria and other phytoplankton in vivo and in situ.     

Cloning and functional expression of the gene encoding the key enzyme for chlorophyll b biosynthesis (CAO) from Arabidopsis thaliana

Chlorophyll (Chl) biosynthesis and degradation are the only biochemical processes on Earth that can be directly observed from satellites or other planets. The bulk of the Chls is found in the light-harvesting antenna complexes of photosynthetic organisms. Surprisingly little is known about the biosynthesis of Chl b, which is the second most abundant Chl pigment after Chl a. We describe here the expression and properties of the chlorophyllide a oxygenase gene (CAO) from Arabidopsis thaliana, which is apparently the key enzyme in Chl b biosynthesis. The recombinant enzyme produced in Escherichia coli catalyses an unusual two-step oxygenase reaction that is the 'missing link' in the chlorophyll cycle of higher plants.     

水分胁迫对牛心朴子叶片光合色素及叶绿素荧光的影响

研究了水分胁迫对牛心朴子叶片光合色素及叶绿素荧光动力学参数的影响。结果表明,在长期的水分胁迫中,牛心朴子叶片的叶绿素a(Chl a)、叶绿素b(Chl b)和类胡萝卜素(Car)含量没有下降或下降不明显。直到处理末期才显著下降;叶片叶绿素荧光动力学参数Fo、Fm、Fv、Fv／Fm变化不大,在处理末期各处理Fo降低,轻度、重度水分胁迫的Fm、Fv、Fv／Fm升高。说明K期水分胁迫后牛心朴子的光合功能受到影响,但牛心朴子仍表现出较强的适应干旱的能力。     

利用PHI数据进行区域性植物生理信息探测与分析

本次试验研究选择两个实验区 :沼泽地和植被茂盛区。利用 2 0 0 0年 9月上旬在黑龙江省大兴安岭地区获取的推帚式超光谱成像 ,(PHI,pushbroomhyperspectralimager)数据进行区域性植物生理量 (主要是叶绿素 )的探测与生态分析。在叶绿素含量探测中 ,结合所获取的成像光谱PHI数据的特点 ,在比较不同技术方法的基础之上 ,选用了有效而简单可靠的RARS(Ratioanalysisofreflectancespectra)指数。该色素指数与植物叶绿素a、b含量拟合的相关系数 (R)达 0 .8以上。利用PHI数据和野外实测植物光谱分别建立沼泽地和植被茂盛区的RARS指数模式 ,分别得到具有指示两试验区的叶绿素a (Chla)、叶绿素b (Chlb)以及类胡萝卜素 (Cars)的参数图像。更进一步地利用Blackburn(1998)所建立的RARS指数与叶绿素浓度之间的强拟合方程 ,相对定量估算了叶绿素a、b浓度的区域性分布 ,清晰地反映出植被生态状况和差异。这与野外实地考察较为一致。     

水分胁迫与复水对地枫皮生理生态特性的影响

以岩溶特有药用植物地枫皮为材料,研究土壤水分胁迫及复水条件下,其叶片光合参数、叶绿素荧光参数及光合色素含量的变化特性,进而探讨其对水分胁迫的生理生态适应性。结果表明:停止供水10 d,水分胁迫地枫皮叶片的P_n(净光合速率)、C_i(胞间CO_2浓度)、G_s(气孔导度)和L_s(气孔限制值)均下降,气孔限制是P_n降低的主要原因;停止供水15 d,水分胁迫地枫皮叶片的P_n日变化呈逐渐下降趋势,上午9:30以后全天的P_n值均接近零,非气孔限制成为P_n下降的主要因素;而对照地枫皮叶片的P_n日变化呈"双峰型",中午P_n下降的主要原因依然是气孔限制。水分胁迫下,地枫皮叶片叶绿素含量降低和Chl_(a/b)升高,减少了叶片对光能的捕获,减轻了光合机构遭受光氧化的破坏,而Car/Chl_(a+b)升高增强了光保护能力。水分胁迫下,地枫皮叶片的初始荧光(F_o)显著增大,最大荧光(F_m)、光系统Ⅱ(PSⅡ)潜在活性(F_v/F_o)和最大光化学效率(F_v/F_m)均显著降低,表明水分胁迫对地枫皮叶片的PSⅡ反应中心和电子传递造成了一定的破坏,从而使其PSⅡ的潜在活性和最大光化学效率降低。复水5 d后,地枫皮的上述生理生态参数均能恢复到对照水平,表明其复水后的生理修复能力很强。     

Metabolic engineering of the Chl d-dominated cyanobacterium Acaryochloris marina: production of a novel Chl species by the introduction of the chlorophyllide a oxygenase gene

In oxygenic photosynthetic organisms, the properties of photosynthetic reaction systems primarily depend on the Chl species used. Acquisition of new Chl species with unique optical properties may have enabled photosynthetic organisms to adapt to various light environments. The artificial production of a new Chl species in an existing photosynthetic organism by metabolic engineering provides a model system to investigate how an organism responds to a newly acquired pigment. In the current study, we established a transformation system for a Chl d-dominated cyanobacterium, Acaryochloris marina, for the first time. The expression vector (constructed from a broad-host-range plasmid) was introduced into A. marina by conjugal gene transfer. The introduction of a gene for chlorophyllide a oxygenase, which is responsible for Chl b biosynthesis, into A. marina resulted in a transformant that synthesized a novel Chl species instead of Chl b. The content of the novel Chl in the transformant was approximately 10% of the total Chl, but the level of Chl a, another Chl in A. marina, did not change. The chemical structure of the novel Chl was determined to be [7-formyl]-Chl d(P) by mass spectrometry and nuclear magnetic resonance spectroscopy. [7-Formyl]-Chl d(P) is hypothesized to be produced by the combined action of chlorophyllide a oxygenase and enzyme(s) involved in Chl d biosynthesis. These results demonstrate the flexibility of the Chl biosynthetic pathway for the production of novel Chl species, indicating that a new organism with a novel Chl might be discovered in the future.     

Effect of UV radiation on pigments of the Antarctic macroalga Leptosomia simplex L.

Impact of UV-A and UV-B radiation on pattern of pigments of the Antarctic macroalga Leptosomia simplex L. was studied during the Polarstern cruise (ANT XII/2) 1994/95 under controlled laboratory conditions. An 8 h exposure to UV-A of 17.6 W m-2 led usually to an increase of carotenoid contents, but to a decrease in contents of chlorophyllide (Chlide) a and chlorophyll (Chl) a. UV-B irradiation (300-320 nm) caused a decrease in contents of Chlide a, lutein, and zeaxanthin, but an increase in contents of Chl a and carotenes. Enhancement of carotenoid contents was attributed to a protection of the photosynthetic apparatus. UV effects on the 15N-ammonium uptake were correlated with the changes in pigment contents.     

Are the photosynthetic membranes of cryptophyte algae inside out?

Summary Cryptomonads are unicellular algae with a unique photosynthetic apparatus, both in structure and pigment composition. A cryptomonad,Rhodomonas lens (R. lens), was studied by conventional electron microscopy, freeze-fracture, and freeze-etch in order to determine whether the thylakoids of this alga are everted with respect to those of other plants, as has been postulated (Gantt et al. 1971,Gantt 1979, 1980) as a means to compensate for the location of the cryptomonad light-harvesting apparatus on the opposite side of the thylakoid membrane from that of related algae. We have characterized the thylakoids of this alga and conclude that they are not everted, but are oriented in the same manner as those of other algae and green plants. Implications for energy transfer are discussed.     

Photosynthetic pigments of plants and lichens inhabiting arctic tundra of West Spitsbergen

The content of photosynthetic pigments and the ratios between them were studied in 71 species of vascular plants, 17 species of Bryophyta, and 10 species of lichens inhabiting West Spitsbergen. With an increase in the level of organization from lichens to vascular plants, the content of photosynthetic pigments (chlorophylls (Chl) and carotenoids (Car)) increased; the Chl a/b ratios and light-harvesting complex values varied independently of organism taxonomy; the Chl/Car ratio tended to increase. The content of pigments is related to taxon advancement at the level of both divisions and higher plant families. In plants inhabiting Arctic region, the pigment content in primitive species was lower than in more advanced ones. In angiosperms inhabiting Spitsbergen, the amount of Chl was lower than in plants inhabiting other botanicgeographical regions.     

Apomissia in “Ochna Serrulata„ Walp

Structural and functional characteristics of the photosynthetic apparatus in 15-day old Brassica rapa plants grown aboard the space shuttle Columbia (STS-87) have been studied. Maintaining of the same growth conditions for control plants was realized using the Orbiter Environmental Simulator in Kennedy Space Center. The main differences in spaceflight plants in comparison with control ones have been shown to be the following. An average volume of one mesophyll palisade cell increased approximately twice and the chloroplast number per cell by 69.8%. Partial volumes of stromal thylakoids, starch grains and plastoglobuli also increased by 19.4%, 20.6% and 2 times accordingly. At the same time, the grana number per chloroplast decreased. Greater diversity of the thylakoid length in grana and a decrease in thylakoid membrane stacking were revealed. A decrease of PSII and PSI light-harvesting antennae has been detected, for PSII by an increase of Chl a/b ratio and kinetics delay in chlorophyll fluorescence induction, and for PSI by a decrease of integral intensity in the excitation spectrum of fluorescence at 735?nm, which indicated a decline of PSI absorption cross-section. Some distortion of PSI complexes have been displayed by fluorescence spectra. A slight decrease in PSII photochemistry yield was detected for the spaceflight material. PSI is concluded to be more susceptible to the microgravity conditions.     

Differences in pigment composition, photosynthetic rates and chlorophyll fluorescence images of sun and shade leaves of four tree species.

The differential pigment composition and photosynthetic activity of sun and shade leaves of deciduous (Acer pseudoplatanus, Fagus sylvatica, Tilia cordata) and coniferous (Abies alba) trees was comparatively determined by studying the photosynthetic rates via CO(2) measurements and also by imaging the Chl fluorescence decrease ratio (R(Fd)), which is an in vivo indicator of the net CO(2) assimilation rates. The thicker sun leaves and needles in all tree species were characterized by a lower specific leaf area, lower water content, higher total chlorophyll (Chl) a+b and total carotenoid (Cars) content per leaf area unit, as well as higher values for the ratio Chl a/b compared to the much thinner shade leaves and needles that possess a higher Chl a+b and Cars content on a dry matter basis and higher values for the weight ratio Chls/Cars. Sun leaves and needles exhibited higher rates of maximum net photosynthetic CO(2) assimilation (P(Nmax)) measured at saturating irradiance associated with higher maximum stomatal conductance for water vapor efflux. The differences in photosynthetic activity between sun and shade leaves and needles could also be sensed via imaging the Chl fluorescence decrease ratio R(Fd), since it linearly correlated to the P(Nmax) rates at saturating irradiance. Chl fluorescence imaging not only provided the possibility to screen the differences in P(N) rates between sun and shade leaves, but in addition permitted detection and quantification of the large gradients in photosynthetic rates across the leaf area existing in sun and shade leaves.     

穿透雨减少下锐齿栎叶片光合色素季节动态及其反射光谱响应

通过林地穿透雨排除的方法模拟降雨减少,测定河南宝天曼自然保护区锐齿栎叶片光合色素含量与反射光谱的季节变化,对减雨处理造成的光合色素变化及其反射光谱的变化进行了定量分析,并探讨了水分控制条件下反射光谱对叶片光合色素变化的响应机制.结果表明: 锐齿栎叶片的光合色素含量和色素比率均呈现明显的季节变化.减雨样地与对照样地叶片的光合色素含量和比率在生长季的各个时期存在差异,其中,叶片叶绿素b(Chl b)含量的差异显著,说明Chl b对减雨处理的敏感性最高,叶片类胡萝卜素(Car)含量的差异较小,说明Car对减雨处理的敏感性相对较弱.550 nm处的光谱反射率对色素季节变化的响应最敏感,以其构造的简单比值指数(SR_750,550)与叶片Chl a、Chl b、总Chl和Car含量的正相关关系显著,光化学反射指数(PRI)与叶片Car/Chl的负相关关系显著.550 nm处的光谱反射率对减雨处理造成的色素变化响应最为敏感.SR_750,550对减雨处理造成的叶片Chl a、Chl b和总Chl的含量变化表现敏感(P<0.01),对Chl a/b的变化不敏感.PRI对减雨处理造成的叶片Car/Chl变化表现敏感(P<0.01).     

Structural and Functional Characteristics of the Mutant Plastids from Extranuclear Variegated Forms of Sunflower

The electron-microscopic analysis of extranuclear variegated forms of sunflower demonstrated that plastids from white leaf areas are practically devoid of inner membrane structures. The mutants and the initial (wild-type) green line were compared by the contents of chlorophyll (Chl), carotenoids, and 70S ribosomes and by the activity of Rubisco. A mutant Var10 line was used to demonstrate that the primary characteristic manifestations of Chl deficiency include the synchronous retardation of the synthesis of a specific Chl precursor, 5-aminolevulinate, a decrease in the Chl a/b ratio to the level below that in the wild type, and the reduction of photosystem (PS) I Chl luminance. The progress of photodestructive processes in the mutant aggravated the listed disturbances; as a result, PSII complexes and light-harvesting complexes gradually degraded. The manifestation of the trait of Chl-deficiency notably varied depending on plant growth conditions (primarily, temperature and illumination regimes). The dependence of this manifestation on light and temperature was observed only at the early stage of development of pigment-containing tissues. When plants terminated this stage under low irradiation, they did not become Chl-deficient, and when their leaves were subsequently transferred to the conditions promoting the maximum pigment anomaly, the destructive processes did not advance in the mutant tissue. The authors assume that the plastom mutations under study impair the control over the expression of the structural plastogenes that determine the synthesis of pigment and protein components of the photosynthetic apparatus, rather than directly damage to the primary structures of plastogenes.