Evaluating the relationship between leaf chlorophyll concentration and SPAD-502 chlorophyll meter readings

Relationships between chlorophyll concentration ([chl]) and SPAD values were determined for birch, wheat, and potato. For all three species, the relationships were non-linear with an increasing slope with increasing SPAD. The relationships for birch and wheat were strong (r ² ∼ 0.9), while the potato relationship was comparatively weak (r ² ∼ 0.5). Birch and wheat had very similar relationships when the chlorophyll concentration was expressed per unit leaf area, but diverged when it was expressed per unit fresh weight. Furthermore, wheat showed similar SPAD–[chl] relationships for two different cultivars and during two different growing seasons. The curvilinear shape of the SPAD–[chl] relationships agreed well with the simulated effects of non-uniform chlorophyll distribution across the leaf surface and multiple scattering, causing deviations from linearity in the high and low SPAD range, respectively. The effect of non-uniformly distributed chlorophyll is likely to be more important in explaining the non-linearity in the empirical relationships, since the effect of scattering was predicted to be comparatively weak. The simulations were based on the algorithm for the calculation of SPAD-502 output values. We suggest that SPAD calibration curves should generally be parameterised as non-linear equations, and we hope that the relationships between [chl] and SPAD and the simulations of the present study can facilitate the interpretation of chlorophyll meter calibrations in relation to optical properties of leaves in future studies.     

北京远郊区臭氧污染及其对敏感植物叶片的伤害

臭氧(O3)是一种氧化性很强且生物危害很大的二次污染物.监测表明北京远郊区O3浓度高于近郊区和城区,经常超过敏感植物O3临界浓度(78.5μg/m3),自然植物的暴露剂量AOT40(超过78.5 μg/m3的空气O3浓度小时值累计量)值达到了98.9mg/m3,可能已经对植物生长造成危害.通过对远郊区O3浓度监测点(北京蟒山森林公园)26种乔木和灌木植物的调查,参考国外有关植物野外观测和模拟实验的植物O3伤害症状特征及植物O3伤害鉴别标准,发现其中15种植物出现了比较明显的O3伤害症状,表现为叶片出现点状、块状黄斑或褐色灼伤状干枯,表明北京远郊区的乔木和灌木已经受到了空气O3污染的危害.另外11种植物也出现了类似O3危害的伤害症状,需要进一步的研究验证是否由O3污染造成.     

Changes of the concentrations of chlorophyll and phaeopigment in grazing experiments

In grazing experiments, the changes in fluorometric determined concentrations of chlorophyll a and phaeopigment are probably less bothered by the interference of other chlorophyll pigments than in analysis of single seawater samples. Theoretically, phaeopigment recovery will be ca 100%, regardless the eventual presence of chlorophyllb. In shipboard experiments in the northern North Sea in May 1983 the chlorophyll consumption by zooplankton was compared with phaeophorbide egestion. Phaeophorbide recovery amounted on average to 67%, comparable with a previous estimate in laboratory experiments by SHUMAN & LORENZEN (1975). Because phaeophorbide concentrations are expressed in chlorophyll equivalents, one third of the chlorophyll consumed is apparently degraded further than phaeophorbide into non-fluorescent material. In grazing experiments withCalanus finmarchicus stages CIV, CV and CVI filtering rates were determined both with the chlorophyll method and with a particle counter. Values roughly doubled with stage and averages per stage did not differ systematically between both methods, suggesting that the natural algae food, dominated by the microflagellateCorymbellus aureus, was not preferred above other seston.     

臭氧浓度升高对香樟叶片光合色素及抗过氧化的影响及其氮素响应

为阐明氮(N)沉降条件下我国亚热带典型常绿树种香樟(Cinnamomum camphora)的臭氧(O3)胁迫响应特征,以1年生幼苗为试验对象,采用开顶气室(OTC)进行模拟研究。O3处理设大气O3(AA)、大气O3+60 nmol/mol(AA+60)、大气O3+120nmol/mol(AA+120)3个水平;N素以硝酸铵(NH4NO3)溶液形式施加,施N量设0(N0)、30(N30)、60(N60)(kg.hm-.2a-1)3个水平。主要考察了叶片膜质过氧化、光合色素、胞质抗坏血酸含量及总抗氧化能力的胁迫响应特征。结果表明:一个生长季(2009年5月15日—2009年9月10日)高浓度O3处理导致试验幼苗叶肉细胞膜脂过氧化程度显著加剧,叶绿素a、叶绿素b、类胡萝卜素含量显著降低;N素施加显著提高了叶绿素含量,但未改变细胞膜脂过氧化水平。叶片总抗氧化能力在AA+120处理下显著提高,但未受N施加影响。还原型抗坏血酸含量在N0处理下随O3浓度升高而降低;在N30及N60处理下随O3浓度升高而增高。施N可通过提高叶片抗坏血酸含量来增强香樟对O3升高的适应能力。研究结论可为O3与N复合污染下,我国亚热带地区典型常绿树种的保护提供科学参考。     

Prolonged incubation with low concentrations of mercury alters energy transfer and chlorophyll (Chl) a protein complexes in Synechococcus 6301: changes in Chl a absorption and emission characteristics and loss of the F695 emission band

Synechococcus PCC 6301 cells grown in the presence of low sublethal levels of (about 2 m) mercury induced alterations in chlorophyll (Chl) a absorption without significant alterations in phycocyanin. Chl a fluorescence emission in Hg²⁺ -raised cells showed a large (about 18 nm) blue shift in the peak emission. No major spectral changes in phycobilisome (PBsome) emission characteristic were noticed, indicating major structural alterations in Chl-protein complexes by incubation with Hg²⁺ ions. Low temperature (77 K) emission spectra of cells grown in the presence of Hg²⁺ showed a loss of the characteristic Chl a emission band at 695 nm (F695), which is known to be linked to photosystem II photochemistry and to originate from the Chl a of core antenna polypeptide CP 47 of photosystem II. The SDS-PAGE polypeptide profile of thylakoids indicates a loss of a polypeptide(s) with a molecular mass between 40 and 60 k Da by Hg²⁺ incubation of cells. Our results suggest that prolonged incubation of Synechococcus 6301 cells with low concentrations of Hg²⁺ affects the Chl a spectral properties and the structure of Chl-protein complexes.     

Impairment of gas exchange and structure in birch leaves (Betula pendula) caused by low ozone concentrations

Summary Injury caused by low O₃ concentrations (0, 0.05, 0.075, 0.1 l 1^-1) was analyzed in the epidermis and mesophyll of fully developed birch leaves by gas exchange experiments and low-temperature SEM: (I) after leaf formation in O₃-free and ozonated air, and (II) after transferring control plants into ozonated air. In control leaves, autumnal senescence also was studied in O₃-free air (III). As O₃ concentration increased, leaves of (I) stayed reduced in size, but showed increased specific weight and stomatal density. The declining photosynthetic capacity, quantum yield and carboxylation efficiency lowered the light saturation of CO₂ uptake and the water-use efficiency (WUE). Carbon gain was less limited by the reduced stomatal conductance than by the declining ability of CO₂ fixation in the mesophyll. The changes in gas exchange were related to the O₃ dose and were mediated by narrowed stomatal pores (overriding the increase in stomatal density) and by progressive collapse of mesophyll cells. The air space in the mesophyll increased, preceded by exudate formation on cell walls. Ozonated leaves, which had developed in O₃-free air (II), displayed a similar but more rapid decline than the leaves from (I). In senescent leaves (III), CO₂ uptake showed a similar decrease as in leaves with O₃ injury but no changes in mesophyll structure and WUE. The nitrogen concentration declined only in senescent leaves in parallel with the rate of CO₂ uptake. A thorough understanding of O₃ injury and natural senescence requires combined structural and functional analyses of leaves.     

Deep chlorophyll a maxima in the Red Sea observed by in-vivo flash fluorometry

An investigation of the hydrography and the population, production and biomass of plankton in the Red Sea, carried out during the METEOR cruise in summer 1987, aimed to describe the ecosystem characteristics during the SW monsoon period. Vertical profiles of in-vivo chlorophyll fluorescence intensity, measured in the presence of chlorphenyl-dimethyl-urea (CMU), are presented. Variations in the fluorescence pattern were observed and assumed to be due to the influence of a reef and surface influx of nutrient rich water from the Gulf of Aden into the Red Sea. This northward influx was driven by SE winds, caused by an unusual northward shift of the innertropical convergence zone up to 20°N in summer 1987. Integrated chlorophyll a values were calculated from fluorescence data. They showed a slight increase from north to south and higher pigment contents in August (8.7–20.2 mg m^–2) than in July (3.3–9.0 mg m^–2), the latter was attributed to the above mentioned influx. Calibration of the fluorescence measurements using cultures of a green alga and cyanobacterium indicated that there may have been an underestimate of the contribution of Oscillatoria populations to the chlorophyll a concentration of the samples. Fluorescence peaks were recorded in the lower part of the euphotic zone, indicating a deep maximum of phytoplankton and/or an increase in chlorophyll fluorescence per unit biomass at these depths.     

Relations between electron transport rates determined by pulse amplitude modulated chlorophyll fluorescence and oxygen evolution in macroalgae under different light conditions

The relationship between O₂-based gross photosynthesis (GP) and in vivo chlorophyll fluorescence of Photosystem II-based electron transport rate (ETR) as well as the relationship between effective quantum yield of fluorescence (Φ_PSII) and quantum yield of oxygen evolution (Φ_{O_2}) were examined in the green algae Ulva rotundata and Ulva olivascens and the red alga Porphyra leucosticta collected from the field and incubated for 3 days at 100 μmol m⁻² s⁻¹ in nutrient enriched seawater. Maximal GP was twice as high in Ulva species than that measured in P. leucosticta. In all species ETR was saturated at much higher irradiance than GP. The initial slope of ETR versus absorbed irradiance was higher than that of GP versus absorbed irradiance. Only under absorbed irradiances below saturation or at values of GP <2 μmol O₂ m⁻² s⁻¹ a linear relationship was observed. In the linear phase, calculated O₂ evolved /ETR molar ratios were closed to the theoretical value of 0.25 in Ulva species. In P. leucosticta, the estimated GP was associated to the estimated ETR only at high irradiances. ETR was determined under white light, red light emitting by diodes and solar radiation. In Ulva species the maximal ETR was reached under red light and solar radiation whereas in P. leucosticta the maximal ETR was reached under white light and minimal under red light. These results are in agreement with the known action spectra for photosynthesis in these species. In the case of P. leucosticta, GP and ETR were additionally determined under saturating irradiance in algae pre-incubated for one week under white light at different irradiances and at white light (100 μmol m⁻² s⁻¹) enriched with far-red light. GP and growth rate increased at a growth irradiance of 500 μmol m⁻² s⁻¹ becoming photoinhibited at higher irradiances, while ETR increased when algae were exposed to the highest growth irradiance applied (2000 μmol m⁻² s⁻¹). The calculated O₂ evolved /ETR molar ratios were close to the theoretical value of 0.25 when algae were pre-incubated under 500–1000 μmol m⁻² s⁻¹. The enrichment by FR light provoked a decrease in both GP and ETR and an increase of nonphotochemical quenching although the irradiance of PAR was maintained at a constant level. In addition to C assimilation, other electron sinks, such as nitrogen assimilation, affected the GP–ETR relationship. The slopes of GP versus ETR or Φ_PSII versus Φ_{O_2} were lower in the algae with the highest N assimilation capacity, estimated as nitrate reductase activity and internal nitrogen contents, i.e., Ulva rotundata and Porphyra leucosticta, than that observed in U. olivascens. The possible mechanisms to explain this discrepancy between GP and ETR are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Differences in above- and below-ground responses to ozone between two populations of a perennial grass

Our study examined the influence of elevated ozone levels on the growth and mycorrhizal colonization of two populations of Elymus glaucus L. (blue wildrye). We hypothesized that ozone would reduce carbon availability to the plants, particularly below ground, and would affect mycorrhizal colonization. Because of the wide geographic range of E. glaucus, two populations of plants were selected from areas of contrasting ozone histories to examine intraspecies variation in response to ozone. Two populations of E. glaucus (southern California versus northern California) exposed in a factorial experiment involving ozone, mycorrhizal inoculation with Glomus intraradices Schenck and Smith, and plant source population. Ozone had a subtle effect on leaf area and number of tillers but did not affect overall root:shoot ratio in either population. The impact of ozone on above-ground growth characteristics was most pronounced in the southern population that came from a high-ozone environment, while below-ground responses such as reduced arbuscular colonization was most pronounced in the northern population which originated in a low-ozone environment. Further analysis of soil characteristics from the northern population of plants revealed a significant reduction in active soil bacterial biomass and an increase in total fungi per gram dry weight soil, suggesting a possible role for ozone in altering soil processes. Whether or not population differences in response to ozone were due to genetic shifts resulting from prior ozone remains to be determined. However, these subtle but important differences in population response to ozone above- and below-ground have significant implications in any attempt to generalize plant response, even within a species. Future research efforts need to include better characterization of intraspecific variation in response to ozone as well as possible adaptive strategies that may result from chronic ozone exposure.     

The relationship between carbon dioxide fixation and chlorophyll a fluorescence during induction of photosynthesis in maize leaves at different temperatures and carbon dioxide concentrations

The rate of CO₂ fixation (F_c) and 680 nm chlorophyll fluorescence emission (F680) were measured simultaneously during induction of photosynthesis in Zea mays L. leaves under varying experimental conditions in order to assess the validity of fluorescence as an indicator of in vivo photosynthetic carbon assimilation. Z. mays leaves showed typical Kautsky fluorescence induction curves consisting of a fast rise in emission (O to P) followed by a slow quenching via a major transient (S-M) to a steady-state (T). After an initial lag, net CO₂ assimilation commenced at a point corresponding to the onset of the S-M transient on the F680 induction curve. Subsequently, F_c and F680 always arrived at a steady-state simultaneously. Decreasing the dark-adaption period increased the rate of induction of both parameters. Alteration of leaf temperature produced anti-parallel changes in induction characteristics of F_c and F680. Reducing the CO₂ level to below that required for saturation of photosynthesis also produced anti-parallel changes during induction, however, at CO₂ concentrations tenfold greater than the atmospheric level the rate of F680 quenching from P to T was appreciably reduced without a similar change in the induction of F_c. Removal of CO₂ at steady-state produced only a small increase in F680 and a correspondingly small decrease in F680 occurred when CO₂ was re-introduced. The complex relationship between chlorophyll fluorescence and carbon assimilation in vivo is discussed and the applicability of fluorescence as an indicator of carbon assimilation is considered.Abbreviations F_c rate of CO₂ fixation - F680 fluorescence emission at 680 nm     

Influence of chlorophyll concentrations on the reliability of measurements with an oxygen electrode when studying photosynthetic efficiency in bioassays using microalgae

Euglena gracilis and Chlamydomonas reinhardtii were used as model organisms to establish the best conditions for studying photosynthetic efficiency using the Light Pipette – experimental system, which enables sensitive detection of changes in oxygen evolution/consumption and an easy collection and digitalisation of data. Chlorophyll concentrations of 0.005, 0.025, 0.050 and 0.075 mgmL^-1 were investigated using different light regimes. Cultures of E. gracilis at the same chlorophyll concentration absorbed more light(measured at 580 μmol m^-2 s^-1) than those of C. reinhardtii. Cell density had a considerable effect on the reliability of measurements. Chlorophyll concentrations between 0.025 mg_Chl ml^-1 and 0.050 mg_Chlml^-1 can be recommended when applying the Light Pipette system in bioassays using microalgae. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of winter stress on photosynthetic electron transport and energy distribution between the two photosystems of pine as assayed by chlorophyll fluorescence kinetics

The fluorescence kinetics of both intact needles and isolated chloroplasts of summer active and winter stressed Pinus sylvestris were measured at both room temperature and 77 K. It was confirmed that winter stress inhibited the photochemical capacity of photosystem II but also that winter stress caused the strongest inhibition of the electron transport at the site where the plastoquinone pool is reduced. Parallel analyses of the fluorescence characteristics of photosystem II (F₆₉₃) and photosystem I (F₇₂₉) during photosystem II trap closure furthermore revealed that the yield of spillover of excitation energy from photosystem II to photosystem I decreased upon winter stress. We suggest that this is because of an increased radiationless decay of excitation energy both at the reaction center and antennae levels of photosystem II. There is, however, also a possibility that the decreased yield of spill-over is accentuated by a partial detachment of the light harvesting chlorophyll a/b complex from photosystem II upon winter stress.Paper presented at the FESPP meeting in Strasbourg (1984).     

On the relationship between the non-photochemical quenching of the chlorophyll fluorescence and the Photosystem II light harvesting efficiency. A repetitive flash fluorescence induction study

Plants respond to excess light by a photoprotective reduction of the light harvesting efficiency. The notion that the non-photochemical quenching of chlorophyll fluorescence can be reliably used as an indicator of the photoprotection is put to a test here. The technique of the repetitive flash fluorescence induction is employed to measure in parallel the non-photochemical quenching of the maximum fluorescence and the functional cross-section (sigma(PS II)) which is a product of the photosystem II optical cross-section a(PS II) and of its photochemical yield Phi(PS II) (sigma (PS II) = a(PS II) Phi(PS II)). The quenching is measured for both, the maximum fluorescence found in a single-turnover flash (F(M) (ST)) and in a multiple turnover light pulse (F(M) (MT)). The experiment with the diatom Phaeodactylum tricornutum confirmed that, in line with the prevalent model, the PS II functional cross-section sigma (PS II) is reduced in high light and restored in the dark with kinetics and amplitude that are closely matching the changes of the F(M) (ST) and F(M) (MT) quenching. In contrast, a poor correlation between the light-induced changes in the PS II functional cross-section sigma (PS II) and the quenching of the multiple-turnover F(M) (MT) fluorescence was found in the green alga Scenedesmus quadricauda. The non-photochemical quenching in Scenedesmus quadricauda was further investigated using series of single-turnover flashes given with different frequencies. Several mechanisms that modulate the fluorescence emission in parallel to the Q(A) redox state and to the membrane energization were resolved and classified in relation to the light harvesting capacity of Photosystem II.     

Evaluation of some fungicides for seed treatment and foliar application in management of damping-off of seedlings and blight of rapeseed caused by Alternaria brassicae

Eighteen fungicides were first evaluated for their effects on growth of Alternaria brassicae and for ascertaining their fungicidal and fungistatic natures in artificial cultures. The chemicals emerging fungicidal in action, were later evaluated for their efficacy as seed treatment and foliar application in the management of damping-off of seedlings and blight of rapeseed separately. Of 18 fungicides tested, six fungicides, viz., Dithane M-45, Dithane Z-78, Ziram, Difolatan-80, Blitox-50 and Benlate completely inhibited the growth of the pathogen and were fungicidal in action. Thiram and Brestan-60, which also caused total growth inhibition, were, however, fungistatic. Benlate (0.1 %) followed by Dithane M-45 was best seed-dressing fungicide for controlling damping-off of seedlings. Dithane M-45 (0.2%) followed by Dithane Z-78 as foliar spray was most effective for controlling the blight and increasing the yield in field trials.     

The rapid yellowing of spruce at a mountain site in the Central Black Forest (Germany). Combined effects of Mg deficiency and ozone on biochemical, physiological and structural properties of the chloroplasts

Biochemical, physiological and ultrastructural changes of the chloroplasts were examined in the course of the rapid yellowing process of spruce (Picea abies (L.) Karst.) at a Mg-deficient and ozone polluted mountain site (Sch?llkopf mountain, Central Black Forest, Germany, 840 m a.s.l.). While at an early stage of yellowing the chlorophyll (Chl) content of the needles decreased slowly, significant changes occurred in the chloroplasts: The lability of the light-harvesting Chl a/b protein complex LHC II increased; the thylakoid cross-sectional area of chloroplasts in the outer mesophyll of the needles decreased, and their Chl fluorescence showed typical changes like the decrease of Fv/Fm and the increase of the photoinhibitory Fv quenching. Later on, the Chl content decreased rapidly, the changes in the chloroplasts continued and the needles turned yellow. Lutein and the pigments of the xanthophyll cycle were enhanced in relation to Chl a. Light and dark reactions of the xanthophyll cycle were highly active indicating efficient proton pumping and NADPH formation. The ratio of nonappressed to appressed thylakoid membranes increased with decreasing Fv/Fm suggesting that structural and fluorescence properties of the chloroplasts were related. The response of the needles to defined shading and improved Mg supply was also examined. The combined effects of strong sun light, low levels of non-Chl-bound Mg (Mg(free)) and ozone concentrations exceeding 80 microg m(-3) are shown to be necessary to induce the rapid yellowing process. For needles with Mg(free) < 0.12 mg g(-1) needle dry matter, the lability of the LHC II was correlated with the ozone concentration suggesting that the destabilization of the LHC II plays a central role in the rapid yellowing process.     

Site factors,foliar nutrient levels and growth of Cordia alliodora plantations in the humid lowlands of Northern Costa Rica

Within the perhumid, Atlantic lowlands of northern Costa Rica, Cordia alliodora plantations were studied in order to explain the observed pattern of growth irregularities. The soils, that were partly used as pastures over long periods, could be classified roughly into two units: (i) red, deeply weathered, slightly acidic soils from Mg-enriched parent material and (ii) brown, strongly acidic soils with high saturation of exchangeable Al (up to 80%).Leaf analysis revealed that Cordia is a highly demanding species in respect to macronutrients. Poorly growing trees in slope position suffered from an insufficient supply of N and P. K/Mg ratios of chlorotic leaves are very low. Soil analysis showed that nutrient deficiencies were related to (i) insufficient soil nutrient reserves of the poor, tropical soils or (ii) to an inhibition of nutrient uptake by soil physical or chemical factors.All sites are characterized by very low K reserves and losses of nutrients that are organically bound (N, P) caused by erosion. In the Mg-rich red soils, low amounts of K lead to K/Mg imbalances. Soil compaction caused by cattle grazing occurs on both soil units. In negatively influences the root development of Cordia, and hence nutrient uptake. In the brown soils, high amounts of exchangeable Al hinder a sufficient supply of nutrients (e.g.P) to the assimilation organs.     

Chlorophyll antenna size adjustments by irradiance in Dunaliella salina involve coordinate regulation of chlorophyll a oxygenase (CAO) and Lhcb gene expression

To elucidate the mechanism of irradiance-dependent adjustments in the chlorophyll antenna size of photosynthesis, we addressed the regulation of expression of genes encoding a variety of chlorophyll biosynthesis enzymes and that of the Lhcb genes in the model organism Dunaliella salina. Among the chlorophyll biosynthesis enzymes tested, only the chlorophyll a oxygenase (CAO) gene responded to changes in the level of irradiance with substantial mRNA level and kinetics of change that were similar to those of the Lhcb genes. Evidence is presented for the operation of a cytosolic signal transduction pathway for the rapid (order of minutes) regulation of both CAO and Lhcb gene expression by irradiance. Inhibitor studies and transient activation of Ca²⁺-dependent kinase suggested phopholipase-C activation to Ca²⁺ release, and activation of a specific Ca²⁺/CaM-dependent protein kinase in this cytosolic signal transduction pathway. The redox state of the plastoquinone pool also serves to regulate CAO and Lhcb gene expression on a slower time scale (hours) and probably serves as a plastidic-origin signal that acts coordinately with the cytosolic signal transduction pathway. It is proposed that irradiance-dependent adjustments in the chlorophyll antenna size occur by coordinate regulation of CAO and Lhcb gene expression via two distinct signal transduction pathways in photosynthetic organisms.     

Photosystem II chlorophyll a fluorescence lifetimes and intensity are independent of the antenna size differences between barley wild-type and chlorina mutants: Photochemical quenching and xanthophyll cycle-dependent nonphotochemical quenching of fluorescence

Photosystem II (PS II) chlorophyll (Chl) a fluorescence lifetimes were measured in thylakoids and leaves of barley wild-type and chlorina f104 and f2 mutants to determine the effects of the PS II Chl a+b antenna size on the deexcitation of absorbed light energy. These barley chlorina mutants have drastically reduced levels of PS II light-harvesting Chls and pigment-proteins when compared to wild-type plants. However, the mutant and wild-type PS II Chl a fluorescence lifetimes and intensity parameters were remarkably similar and thus independent of the PS II light-harvesting antenna size for both maximal (at minimum Chl fluorescence level, F_o) and minimal rates of PS II photochemistry (at maximum Chl fluorescence level, F_m). Further, the fluorescence lifetimes and intensity parameters, as affected by the trans-thylakoid membrane pH gradient (pH) and the carotenoid pigments of the xanthophyll cycle, were also similar and independent of the antenna size differences. In the presence of a pH, the xanthophyll cycle-dependent processes increased the fractional intensity of a Chl a fluorescence lifetime distribution centered around 0.4–0.5 ns, at the expense of a 1.6 ns lifetime distribution (see Gilmore et al. (1995) Proc Natl Acad Sci USA 92: 2273–2277). When the zeaxanthin and antheraxanthin concentrations were measured relative to the number of PS II reaction center units, the ratios of fluorescence quenching to [xanthophyll] were similar between the wild-type and chlorina f104. However, the chlorina f104, compared to the wild-type, required around 2.5 times higher concentrations of these xanthophylls relative to Chl a+b to obtain the same levels of xanthophyll cycle-dependent fluorescence quenching. We thus suggest that, at a constant pH, the fraction of the short lifetime distribution is determined by the concentration and thus binding frequency of the xanthophylls in the PS II inner antenna. The pH also affected both the widths and centers of the lifetime distributions independent of the xanthophyll cycle. We suggest that the combined effects of the xanthophyll cycle and pH cause major conformational changes in the pigment-protein complexes of the PS II inner or core antennae that switch a normal PS II unit to an increased rate constant of heat dissipation. We discuss a model of the PS II photochemical apparatus where PS II photochemistry and xanthophyll cycle-dependent energy dissipation are independent of the Peripheral antenna size.Abbreviations Ax antheraxanthin - BSA bovine serum albumin - c_x lifetime center of fluorescence decay component x - CP chlorophyll binding protein of PS II inner antenna - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DTT dithiothreitol - f_x fractional intensity of fluorescence lifetime component x - F_m, F_m maximal PS II Chl a fluorescence intensity with all Q_A reduced in the absence, presence of thylakoid membrane energization - F_o minimal PS II Chl a fluorescence intensity with all Q_A oxidized - F_v=F_m–F_o variable level of PS II Chl a fluorescence - HPLC high performance liquid chromatography - k_A rate constant of all combined energy dissipation pathways in PS II except photochemistry and fluorescence - k_F rate constant of PS II Chl a fluorescence - LHCIIb main light harvesting pigment-protein complex (of PS II) - N_pig mols Chl a+b per PS II - NPQ=(F_m/F_m–1) nonphotochemical quenching of PS II Chl a fluorescence - PAM pulse-amplitude modulation fluorometer - PFD photon-flux density, mols photons m^–2 s^–1 - PS II Photosystem II - P680 special-pair Chls of PS II reaction center - Q_A primary quinone electron acceptor of PS II - V_x violaxanthin - w_x width at half maximum of Lorentzian fluorescence lifetime distribution x - Zx zeaxanthin - pH trans-thylakoid proton gradient - % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% GabaqaaiGacaGaamqadaabaeaafiaakeaacqGH8aapcqaHepaDcqGH% +aGpdaWgaaWcbaGaamOraiaad2gaaeqaaaaa!4989!\[< \tau > _{Fm}\],% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% GabaqaaiGacaGaamqadaabaeaafiaakeaacqGH8aapcqaHepaDcqGH% +aGpdaWgaaWcbaGaamOraiaad+gaaeqaaOGaeyypa0Zaaabqaeaaca% WGMbWaaSbaaSqaaiaadIhaaeqaaOGaam4yamaaBaaaleaacaWG4baa% beaaaeqabeqdcqGHris5aaaa!50D3!\[< \tau > _{Fo} = \sum {f_x c_x }\] average lifetime of Chl a fluorescence calculated from a multi-exponential model under F_m, F_o conditions     

Mercury inhibits the non-photochemical reduction of plastoquinone by exogenous NADPH and NADH: evidence from measurements of the polyphasic chlorophyll a fluorescence rise in spinach chloroplasts

Chlorophyll a fluorescence rise kinetics (from 50 μs to 1 s) were used to investigate the non-photochemical reduction of the plastoquinone (PQ) pool in osmotically broken spinach chloroplasts (Spinacia oleracea L.). Incubation of the chloroplasts in the presence of exogenous NADPH or NADH resulted in significant changes in the shape of the fluorescence transient reflecting an NAD(P)H-dependent accumulation of reduced PQ in the dark, with an extent depending on the concentration of NAD(P)H and the availability of oxygen; the dark reduction of the PQ pool was saturated at lower NAD(P)H concentrations and reached a higher level when the incubation took place under anaerobic conditions than when it occurred under aerobic conditions. Under both conditions NADPH was more effective than NADH in reducing PQ, however only at sub-saturating concentrations. Neither antimycin A nor rotenone were found to alter the effect of NAD(P)H. The addition of mercury chloride to the chloroplast suspension decreased the NAD(P)H-dependent dark reduction of the PQ pool, with the full inhibition requiring higher mercury concentrations under anaerobic than under aerobic conditions. This is the first time that this inhibitory role of mercury is reported for higher plants. The results demonstrate that in the dark the redox state of the PQ pool is regulated by the reduction of PQ via a mercury-sensitive NAD(P)H-PQ oxidoreductase and the reoxidation of reduced PQ by an O₂-dependent pathway, thus providing additional evidence for the existence of a chlororespiratory electron transport chain in higher plant chloroplasts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Light-harvesting proteins of diatoms: Their relationship to the chlorophyll a/b binding proteins of higher plants and their mode of transport into plastids

Summary We have cloned and characterized members of a gene family encoding polypeptide constituents of the fucoxanthin, chlorophyll a/c protein complex, a light-harvesting complex associated with photosystem II of diatoms and brown algae. Three cDNA clones encoding proteins associated with this complex in the diatom Phaeodactylum tricornutum have been isolated. As deduced from the nucleotide sequences, these light-harvesting proteins show homology to the chlorophyll a/b binding polypeptides of higher plants. Specifically, the N-terminal regions of the fucoxanthin, chlorophyll a/c-binding proteins are homologous to the chlorophyll a/b binding proteins in both the third membrane-spanning domain and the stroma-exposed region between membrane-spanning domains 2 and 3. Like the chlorophyll a/b-binding proteins, the mature fucoxanthin, chlorophyll a/c polypeptides have three hydrophobic -helical domains which could span the membrane bilayer. The similarities between the two light-harvesting proteins might reflect the fact that both bind chlorophyll molecules and/or might be important for maintaining certain structural features of the complex. There is little similarity between the N-terminal sequences of the primary translation products of the fucoxanthin, chlorophyll a/c proteins and any transit sequences that have been characterized. Instead, the N-terminal sequences have features resembling those of signal sequences. Thus either transit peptides used in P. tricornutum show little resemblance to those of higher plants and green algae or the nuclear-encoded plastid proteins enter the organelle via a mechanism different from that used in higher plants.