Different responses of photosynthesis and flow cytometric signals to iron limitation and nitrogen source in coastal and oceanic Synechococcus strains (Cyanophyceae)

Iron plays an important role in marine primary productivity, and Synechococcus species as major contributors to the total photosynthetic biomass in the world’s oceans might be limited by iron supply in some regions. The present study aimed to compare the photosynthesis and flow cytometric signals of four Synechococcus strains grown under different iron concentrations with either nitrate or ammonium as the sole nitrogen source. Two oceanic strains were much more sensitive to iron limitation than two coastal strains. The inhibition of iron limitation on the growth, maximal PSII photochemical yield, maximal rate of relative electron transport and photochemical quenching of the two oceanic strains was higher than for their coastal counterparts. Under iron limitation condition, the connectivity factor between individual photosynthetic units (ρ) increased for the two coastal strains, while decreased for the two oceanic strains. Furthermore, iron limitation accelerated the Q _A re-oxidation of the two oceanic strains and the PQ pool re-oxidation of the two coastal strains. Under iron limitation condition, the cell size of the two coastal strains and intracellular pigment concentrations of the two oceanic strains decreased, while the side light scatter/front light scatter (SS/FS) ratio of the two coastal strains increased. In contrast to iron limitation, nitrogen source only marginally affected the photosynthesis of the four Synechococcus strains. Ammonium enhanced the growth of the two coastal strains under iron-replete condition. For the two oceanic strains, ammonium increased their cell size and decreased their SS/FS ratio and intracellular pigment concentrations under iron-deplete and iron-replete conditions.     

Release of zooxanthellae with intact photosynthetic activity by the coral<Emphasis Type="Italic"> Galaxea fascicularis</Emphasis> in response to high temperature stress

Damage to zooxanthellae photosynthetic apparatus has been proposed to be the underlying mechanism of coral bleaching, but how the expulsion of zooxanthellae is triggered is still not understood. The present study compared the photosystem II (PSII) functioning and overall photosynthesis of retained and released zooxanthellae from the reef-building coral Galaxea fascicularis exposed to high temperature stress. The use of pulse-amplitude-modulated (PAM) fluorometry for isolated zooxanthellae was validated and used to measure photosynthesis. There was no significant difference in PSII functioning and the overall photosynthesis between retained zooxanthellae, which were isolated immediately after stress treatment, and those released from the coral exposed to either 30 or 32°C, while the zooxanthellae population released at 28°C showed significantly lower PSII functioning than those retained in the polyps. The release of healthy-looking zooxanthellae by polyps exposed to elevated temperatures was significantly higher than those in the control (28°C). Higher release of undischarged cnidae, indicative of host cell necrosis or detachment, was observed in 32°C treatments. These findings indicate that the zooxanthellae released in 30 or 32°C treatments exhibited normal morphology and intact photosynthetic activity. The present results strongly suggest that the release of zooxanthellae from G. fascicularis at 30 or 32°C is a non-selective process with respect to the zooxanthellar PSII functioning and thus the host seems to be the first partner to be physiologically affected in temperature-induced bleaching.Communicated by T. Ikeda, Hakodate     

An annual carbon budget for the kelp Laminaria longicruris

Oxygen evolution and uptake by whole thalli of the large marine alga Laminaria longicruris de la Pylaie were measured for 24 h, once every 2 weeks for a year, using large chambers to incubate the plants on the sea bed. Diel rates of photosynthesis and respiration were calculated from these measurements and continuous light measurements were used to extrapolate the data between observation dates. The resulting estimates were combined with measurements of growth and carbon content to give an annual carbon budget for a typical mature plant. Annual net assimilation was 6.8 mgC per cm² of frond surface (71 cal cm^-2). Approximately 45% of this appeared in the production of new frond tissue, and a further 12% was accounted for by storage of carbon in mature frond tissue. About 8% was needed for stipe growth, and the remaining 35% was assumed to be lost as dissolved organic carbon. Diel net photosynthetic rates reached a maximum in June and July and were negative only in November, indicating an ability to produce a photosynthetic surplus throughout winter. In early winter the plants drew on stored reserves to supplement photosynthesis in providing carbon for growth, but from January onwards photosynthesis provided more than enough carbon for growth.     

Short-term physiological indicators of N deficiency in phytoplankton: a unifying model

Nitrogen resupply to N-limited microalgae elicits several rapid physiological responses which have been used as indicators of N deficiency. These include a stimulation of dark respiration and dark carbon fixation. In addition, N resupply to some microalgae results in a transient suppression of photosynthetic carbon fixation. Long term, N enrichment results in an increase in the rate of photosynthesis and ultimately in the rate of growth. In this report these physiological indicators of N deficiency are documented as a function of steady-state growth rate in Selenastrum minutum Naeg. Collins (Chlorophyta). Based on previous biochemical and physiological studies, we suggest that these short-term responses are a reflection of redirection of photosynthetic carbon flow to the process of N assimilation. A unifying model is proposed that interrelates these responses to N resupply.     

Photosynthetic characteristics of marine Synechococcus spp. with special reference to light environments near the bottom of the euphotic zone of the open ocean

The present study aimed to resolve the question why marine Synechococcus spp. abundantly occur even at the bottom of the euphotic zone in the Kuroshio are. Photosynthesis under such conditions was examined using simulated blue-green model light (BGL). Results indicated that photosynthesis of marine Synechococcus spp. under BGL is as active enough to support growth of these organisms. Examination of light-harvesting under BGL indicated that active photosynthesis is permitted by an unusually high abundance of phycoerythrin (PE), which is the main light-harvesting pigment for photosystem II (PSII), due to a phycobilisome (PBS) structure which is different from ordinary hemidiscoidals. Although the absorption maximum of PE is located at longer wavelengths than the energy maximum of BGL, PE was found to absorb BGL significantly. Thus, BGL cannot be a typical photosystem I (PSI) light. PSII is also significantly excited by BGL. Carotenoids, which largely absorb BGL, were found to be effective in light-harvesting for PSI. Based on the results obtained, possible reasons why marine Synechococcus spp. commonly occur in warm waters were discussed. Two strains of Synechococcus spp. isolated from the Gulf Stream in 1981 and from Kuroshio, Japan in 1983 were used in the present study.     

铁限制对浮游植物生长和群落组成的影响研究综述

Fe是浮游植物生长必需的微量元素,其供应对水体中浮游植物的生物量、生长速率以及种群组成均具有重要的影响。从Fe在浮游植物新陈代谢中的作用出发,重点对近年来国内外有关Fe对浮游植物光合作用、营养盐吸收利用以及浮游植物群落组成的影响等方面的研究进展作了较详细的介绍,认为：（1）Fe通常是HNLC海域中初级生产力的主要限制因子之一,Fe限制会导致浮游植物细胞色素密度以及相应的光合叶绿素减少,从而降低其光合作用速率,导致生长缓慢;（2）Fe限制还能改变浮游植物吸收营养盐（N、P、Si等）的速率和比例,影响浮游植物的种间竞争,进而影响其群落结构;（3）Fe加富能够改变水体中浮游植物的优势种群,在海洋中表现为硅藻占优势,而在淡水湖泊中则表现为绿藻和细菌占优势;（4）在淡水湖泊中总Fe含量普遍较高,但浮游植物可利用Fe的含量受水体中有机配体的种类和数量的影响,在一定条件下Fe也可能成为浮游植物生长的限制因子,这对进一步认识湖泊水华暴发的机制具有一定的意义;（5）有学者提出将施加Fe作为一种生态手段,来提高HNLC海域的初级生产力,从而缓解由于大气中CO2浓度增加而导致的全球变暖的趋势;相反地,将降低浮游植物可利用Fe含量作为一种生态手段,来控制富营养化湖泊中藻类的生物量及群落结构,从而缓解日益严重的水华问题,值得进一步研究和探讨。     

外源Hg胁迫对3种烟草品种叶绿素含量和光合效应的影响

为研究不同浓度汞(Hg)对烟草光合作用的影响,选择福建省3个主栽烟草品种(翠碧1号、K326、云烟87)幼苗进行盆栽试验,设置0、1、2、4、8、16 mg·kg~(-1)共6个浓度组。结果表明:(1)3种烟草叶片叶绿素含量与对照比均无显著差异(P0.05),但F_v/F_m、F_v/F_o、PI_(ABS)随胁迫浓度增加均呈下降趋势,可见Hg胁迫下烟草叶绿素含量和光合强度没有必然的相关性。(2)在较高浓度(4 mg·kg~(-1))Hg胁迫下,OJIP曲线改变了形状,表明Hg胁迫对烟草叶片光合机构影响主要是PSⅡ及光系统反应中心受到损伤,光合电子传递过程受到抑制,这可能是烟草叶片光合效应显著下降的主要因素。(3)烟草叶片PSII单位反应中心比活性参数ABS/RC、TRo/RC、DIo/RC与胁迫浓度正相关,ETo/RC和RC/CSo与胁迫浓度呈负相关,在较高浓度Hg胁迫下烟草叶片通过耗散过剩的光能和提高多余能量消耗量来保护光合机构免受更大的伤害,表现出较强的自我调节能力。     

Carbon fixation and coccolith detachment in the coccolithophore Emiliania huxleyi in nitrate-limited cyclostats

This study addresses carbon fixation and coccolith production and detachment in the cosmopolitan species Emiliania huxleyi (Lohmann) Hay et Mohler, under conditions of nitrate limitation and high light typical of surface water in the ocean. Cells were grown under controlled growth conditions using nitrate-limited cyclostat cultures at four growth rates between 0.2 and 0.7 d⁻¹ in 1995. Both photosynthesis and calcification rates increased with growth rate. Coccolith dimensions remained constant at all cell growth rates. Specific rates of coccolith detachment also increased linearly with cell-specific growth rate at a ratio not significantly different from 1.00. Estimates of coccolith carbon content decreased with increasing cell growth rates. Received: 18 March 1997 / Accepted: 8 October 1998     

Impact of a temporal salinity decrease on growth and nitrogen metabolism of the marine diatom Skeletonema costatum in continuous cultures

In 1987 effects of salinity fluctuations on growth of the centric diatom Skeletonema costatum (Greville) Cleve, isolated from the brackish Krammer estuary (SW Netherlands) in 1981, were investigated. Continuous cultures (12 h light: dark cycle) of S. costatum were adapted to constant salinity in natural (16.1) and synthetic (13.5) media. For several days the ammonium-limited cultures were exposed to a salinity fluctuation (minimum 4.8). Decreasing salinity caused an inhibition of photosynthesis, dark respiration and cell growth. Cellular pools of glucose decreased. While the carbohydrate content remained constant, the protein content increased slightly. Net carbon fixation was more inhibited than nitrogen assimilation. Ammonium accumulated during a salinity decrease; a total decline of the overcapacity of ammonium uptake was noticed and nitrogen limitation was relieved. Amino acid pools decreased, probably as a result of excretion (osmoregulation). The enzymes invoilved in ammonium assimilation showed an increased activity. Cellular activities were resumed during a salinity increase. Chlorophyll a increased; photosynthesis, ammonium uptake and growth were stimulated. The ammonium uptake capacity recovered completely; glutamic acid accumulation and increased glutamate-dehydrogenase (GDH) activity indicated supplementary ammonium assimilation via GDH. The activities of glutamine synthetase/glutamate synthase (GS/GOGAT) and GDH stabilized, and the cells returned to steady state under ammonium limitation.Communication no. 426 Delta Institute for Hydrobiological Research, Yerseke, The Netherlands     

Products of photosynthesis by marine phytoplankton: the effect of environmental factors on the relative rates of protein synthesis

A method is presented by which the gross pattern of photosynthetic carbon-dioxide fixation in marine phytoplankton can be determined. It depends on differential solvent extraction yielding an ethanol-soluble, a hot TCA-soluble (polysaccharide) and a residue (protein) fraction. Using this fractionation technique, the effects of various environmental factors on the pattern of photosynthesis by the marine diatom Phaeodactylum tricornutum (Bohlin) have been investigated. Low light intensities and increasing degrees of nitrogen limitation in a chemostat increase markedly the relative rates of protein synthesis. Growth of the alga at lower temperatures also increases the proportion of carbon incorporated into the protein fraction. This increased protein syntheses is generally at the expense of the polysaccharide fraction. Preliminary experiments have established the suitability of this fractionation method for natural populations of phytoplankton and have shown similar effects of light intensity on the relative rates of protein synthesis.     

Effect of blue light on early sporophyte development of Saccharina japonica (Phaeophyta)

Growth and photosynthesis in the blade of Saccharina sporophytes are strongly stimulated by blue light. However, little is known about the effect of blue light on the early development and longitudinal photosynthesis profile of Saccharina sporophytes. In this study, S. japonica sporelings were cultured under blue or red light for 8 weeks. Blue light affected longitudinal, tangential cell divisions and tissue differentiation early in sporophyte development. The number of latitudinal cells in the blade under blue light was over fivefold that under red light. In addition, the number of cell layers was higher in the growing point than in the blade under blue light, whereas sporelings grown under red light contained only a single cell layer. Under blue light, the photosynthetic capacities of the growing region, blade and stipe were similar, and the maximum relative electron transport rate was even lower in the growing point than in the blade. The longitudinal photosynthesis profile suggested that blue light stimulated the enzymes participating in light-independent carbon fixation in the growing point and accordingly was less dependent on high light irradiances. Collectively, the results indicated that blue light promotes the early development of S. japonica sporophytes, which was attributed to both photomorphogenetic responses and photosynthetic reactions.     

Questions on the mechanism of temperature adaptation in marine phytoplankton

The rate of light-saturated photosynthesis in 3 marine algae [Phaeodactylum tricornutum Bohlin, Nitzschia closterium (Ehrenberg) Smith and Dunaliella tertiolecta Butcher] varies during growth in batch culture. The photosynthetic rare declines most rapidly during growth at the higher temperatures. Because of these changes in photosynthesis rate, the previously reported enhanced photosynthetic abilities caused by growth at lower temperatures (generally interpreted as evidence for higher enzyme levels) can only be observed when measurements are made late in the exponential phase or after the onset of the stationary phase of growth. When allowance is made for the earlier peak of photosynthetic ability in cultures growing at higher temperatures, there is no evidence for adaptation to lower temperatures being caused by increased levels of the enzymes required for carbon-dioxide fixation. When the changes due to growth in batch culture are taken into account, certain effects of temperature can be recognized. the dry weight: chlorophyll ratio of all 3 algae increases with decreasing growth temperatures. For P. tricornutum and N. closterium, growth at lower temperatures reduces the cellular content of chlorophyll a, but has little effect on the chlorophyll content of D. tertiolecta. The dry weight: cell-number ratio of D. tertiolecta and P. tricornutum increases with lower growth temperatures, but growth temperature has little effect on the cell mass of N. closterium. Growth of the 3 algae at lower temperatures does not increase their ability to photosynthesize at these lower temperatures. Rather, it reduces their ability to assimilate carbon dioxide at the higher temperatures.     

Development of the ability to take up L-lysine by the diatom Phaeodactylum tricornutum

Freshly harvested cells of Phaeodactylum tricornutum Bohlin grown with nitrate, ammonium or lysine as a sole nitrogen source had a low ability to take up lysine or arginine, but this ability increased when cells were deprived, over 48 h, of either nitrogen or carbon. The effects of nitrogen and carbon deprivation were additive, and the uptake ability was greatest in cells incubated in darkness in nitrogen-free medium. Uptake ability increased in cells illuminated in the presence of 10^-5 M 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) an inhibitor of photosynthetic electron transport. An inverse relationship between rate of development of the uptake system and rate of photosynthesis was also established. Development of the uptake system was prevented by cycloheximide or by anaerobiosis. Following transfer to a normal nitrate medium, illuminated cells lost the lysineuptake system by dilution as the cells grew. There was a linear and positive correlation between the initial rate of uptake of lysine and the maximum concentration which was maintained in the cells when equilibrium was reached, indicating that transinhibition of lysine uptake may occur and that the extent of this inhibition is related to the size of the internal amino acid pool. The relevance of the findings to the growth of phytoplankton in natural waters is discussed.     

Flux capacities and acclimation costs in Trichodesmium from the Gulf of Mexico

Phytoplankton function and acclimation are driven by catalytic protein complexes that mediate key physiological transformations, including generation of photosynthetic ATP and reductant, and carbon and nitrogen fixation. Quantitation of capacities for these processes allows estimation of rates for key ecosystem processes, and identification of factors limiting primary productivity. We herein present molar quantitations of PSI, PSII, ATP synthase, RuBisCO and the Fe protein of nitrogenase of Trichodesmium collected from the Gulf of Mexico, in comparison to determinations for a range of cyanobacteria growing in culture. Using these measurements, estimates were generated for Trichodesmium capacities for carbon fixation of 1–3.4 g C g chl a ⁻¹ h⁻¹ and nitrogen fixation of 0.06–0.17 g N g chl a ⁻¹ h⁻¹, with diel variations in capacities. ATP synthase levels show that ATP synthesis capacity is sufficient to support these levels of carbon and nitrogen fixation, and that ATP synthase levels change over the day in accordance with the ATP demands of nitrogenase and RuBisCO activity. Levels of measured complexes indicate that Trichodesmium manifests n-type diel light acclimation through rapid changes in RuBisCO:PSII, supported by significant investment of cellular nitrogen. The plasticity in the levels and stoichiometry of these core complexes show that changes in the abundance of core protein complexes are an important component of acclimation and regulation of metabolic function by Trichodesmium populations. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Light-dependency of nitrate uptake by phytoplankton over the spring bloom in Auke Bay,Alaska

The effect of light intensity on nitrate uptake by natural populations of phytoplankton was examined by ¹⁵N traceruptake experiments during the spring (March–May 1987) in Auke Bay, Alaska. The data were fit to a rectangular hyperbolic model which included a term for dark uptake. Three types of curves described nitrate uptake as a function of light intensity. The first (Type I) had a low half-saturation light intensity (K _I), low chlorophyll-specific uptakes rates, no dark uptake and occasional photoinhibition. These were observed during a period of biomass decrease, accompanied by low daily light and strong wind, prior to the major bloom. The second type (Type II) had relatively high K _I, high chlorophyll-specific uptake rates, and no dark uptake. Type II curves were observed during most of the period prior to nitrate depletion in the surface waters. Types I and II both appeared prior to nitrate depletion in the water and reflected variations in the light history of the phytoplankton population. The third type (Type III) occurred in nitrate-deplete conditions, when nitrate uptake was less dependent on light intensity (i.e., high rates of dark uptake and lower K _I). Decreased light-dependency during this period was coupled with physiological nitrogen deficiency in the population. Comparing these parameters to those of photosynthetic carbon fixation, K _Ivalues of nitrate uptake were generally higher than those of photosynthesis prior to nitrate depletion, and lower during nutrient-deplete conditions.     

Succession and growth limitation of phytoplankton in the Gulf of Bothnia (Baltic Sea)

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca. four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothanian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothanian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, the conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.     

Effects of crude oil and chemical dispersant on photosynthesis in the brain coral Diploria strigosa

An eight-hour exposure of Diploria strigosa (Dana) to a mixture of Arabian Light crude oil (19 ppm) and the chemical dispersant “Corexit 9527” (1 ppm) in a flowing seawater system reduced photosynthesis by symbiotic zooxanthellae by 85%, while either oil or dispersant alone had no effect. The greatest effect of crude oil plus dispersant occurred in the incorporation of photosynthetic products into lipids. Synthesis of was esters and triglycerides, the major storage lipids, was particularly affected. Total carbon fixation was restored within 3–5 h after treatment, and lipid synthesis was restored within 5–24 h after exposure.     

低温胁迫对6种珍贵树种苗木光合荧光特性的影响

以格木（Erythrophleum fordii）、降香黄檀（Dalbergia odorifera）、闽楠（Phoebe bournei）檀香（Santalum album）、铁刀木（Cassia siamea）和樟树（Cinnamomum camphora）6种珍贵树种苗木为研究对象,分析自然降温过程中苗木相对叶绿素含量、气体交换参数及叶绿素荧光参数等指标的变化,探讨低温胁迫对这6种苗木光合荧光特性的影响,并利用隶属函数法对6种珍贵树种耐寒能力进行了评价,以期了解这几种植物的抗寒能力差异及低温对其光合能力的影响,为扩大引种和栽培提供依据。结果表明,与对照相比,低温胁迫下6种珍贵树种苗木净光合速率（Pn）、气孔导度（Gs）和蒸腾速率（Tr）均有不同程度的下降,其中,格木、降香黄檀、闽楠、檀香、铁刀木净光合效率的下降很大程度上来源于非气孔因素抑制,而樟树净光合速率下降可能来源于气孔限制因素。闽楠、檀香和樟树水分利用效率（WUE）呈上升趋势,而格木与降香黄檀WUE均有不同程度的降低,表明闽楠、檀香和樟树能较好地协调碳同化和水分耗散。低温胁迫下6种珍贵树种Fm均有所下降,表明低温可对珍贵树种苗木叶片PSII反应中心的电子传递潜力产生明显的抑制,致使珍贵树种PSII的光能转换效率降低。降香黄檀、闽楠、檀香、铁刀木和樟树经历2次低温胁迫后qP呈现出持续下降的趋势,表明珍贵树种PSII反应中心的开放程度降低。在2次低温胁迫间格木、降香黄檀、闽楠和铁刀木qN差异不显著（p〉0.05）,表明珍贵树种具有过剩光能耗散机制,保护光合机构免受破坏。相关性分析结果表明,Pn与Gs、Tr、Fv/Fm、qP、qN、ETR和Fm存在极显著相关关系（p〈0.01）,表明Gs、Tr、Fv/Fm、qP、qN、ETR和Fm均可作为衡量植物光合能力的参数。隶属函数法分析结果表明,6种珍贵树种抗寒能力依次为格木〉樟树〉闽楠=檀香=铁刀木〉降香黄檀。总之,?     

Modeling seasonal course of carbon fluxes and evapotranspiration in response to low temperature and moisture in a boreal Scots pine ecosystem

Environmental conditions act above and below ground, and regulate carbon fluxes and evapotranspiration. The productivity of boreal forest ecosystems is strongly governed by low temperature and moisture conditions, but the understanding of various feedbacks between vegetation and environmental conditions is still unclear. In order to quantify the seasonal responses of vegetation to environmental factors, the seasonality of carbon and heat fluxes and the corresponding responses for temperature and moisture in air and soil were simulated by merging a process-based model (CoupModel) with detailed measurements representing various components of a forest ecosystem in Hyytiälä, southern Finland. The uncertainties in parameters, model assumptions, and measurements were identified by generalized likelihood uncertainty estimation (GLUE). Seasonal and diurnal courses of sensible and latent heat fluxes and net ecosystem exchange (NEE) of CO₂ were successfully simulated for two contrasting years. Moreover, systematic increases in efficiency of photosynthesis, water uptake, and decomposition occurred from spring to summer, demonstrating the strong coupling between processes. Evapotranspiration and NEE flux both showed a strong response to soil temperature conditions via different direct and indirect ecosystem mechanisms. The rate of photosynthesis was strongly correlated with the corresponding water uptake response and the light use efficiency. With the present data and model assumptions, it was not possible to precisely distinguish the various regulating ecosystem mechanisms. Our approach proved robust for modeling the seasonal course of carbon fluxes and evapotranspiration by combining different independent measurements. It will be highly interesting to continue using long-term series data and to make additional tests of optional stomatal conductance models in order to improve our understanding of the boreal forest ecosystem in response to climate variability and environmental conditions.     

Phycoerythrin and photosynthesis of the pelagic blue-green alga Trichodesmium thiebautii in the waters of Kuroshio,Japan

The photosynthetic function of phycoerythrin was investigated in the alga Trichodesmium thiebautii from the waters of Kuroshio, Japan. The spectroscopic characteristics of the in vivo and isolated T. thiebautii phycoerythrin pigments are identical, and have 3 absorption bands at 495, 547 and 562 nm. Light at the wavelengths corresponding to each absorption band of phycoerythrin is equally efficient in T. thiebautii photosynthesis, indicating that phycoerythrin is active in trapping light energy for photosynthesis. In the natural habitat, phycoerythrin is considered to be the main photosynthetic pigment in T. thiebautii photosynthesis.