Protein-carbohydrate productivity of Chlorella and efficiency of use of light of varying spectral composition in photosynthesis]

Data are presented on the intensity of carbohydrates and protein biosynthesis during the cultivation of Chlorella asynchroneous culture illuminated with light different spectral regions. High photosynthetic activity of absorbed radiation of the spectrum green region is found.     

Balancing the energy flow from captured light to biomass under fluctuating light conditions

The balance of energy flow from light absorption into biomass was investigated under simulated natural light conditions in the diatom Phaeodactylum tricornutum and the green alga Chlorella vulgaris. The energy balance was quantified by comparative analysis of carbon accumulation in the new biomass with photosynthetic electron transport rates per absorbed quantum, measured both by fluorescence quenching and oxygen production. The difference between fluorescence- and oxygen-based electron flow is defined as 'alternative electron cycling'. The photosynthetic efficiency of biomass production was found to be identical for both algae under nonfluctuating light conditions. In a fluctuating light regime, a much higher conversion efficiency of photosynthetic energy into biomass was observed in the diatom compared with the green alga. The data clearly show that the diatom utilizes a different strategy in the dissipation of excessively absorbed energy compared with the green alga. Consequently, in a fluctuating light climate, the differences between green algae and diatoms in the efficiency of biomass production per photon absorbed are caused by the different amount of alternative electron cycling.     

Green light drives photosynthesis in mosses

Temperate forests are characterised by variable light quality (i.e. spectral composition of light) at or near the forest floor. These understory environments have a high concentration of green light, as red and blue light are preferentially absorbed by upper canopy leaves. Understory species may be well-adapted for using green light to drive photosynthesis. Angiosperms have been shown to use green light for photosynthesis, but this ability has not been demonstrated in shade-dwelling bryophytes. In this study, net photosynthetic rate (P_N) of three temperate understory species of moss (Dichodontium pellucidum (Hedw.) Schimp., Leucobryum albidum (Brid. ex P.Beauv) Lindb. and Amblystegium serpens (Hedw.) Schimp.) was measured under green, red?+?blue, and red?+?blue?+?green light to assess green light use efficiency. All three species were capable of photosynthesising beyond their respiratory demands using solely green light, with higher green light use efficiency measured in plants collected from areas with greater canopy cover, suggesting growth in a green light concentrated environment increases green light use efficiency. Each species was also collected from sites differing in their degree of canopy cover and grown under three light treatments (high light, low light, and green light). Photosynthetic efficiency (chlorophyll fluorescence), tissue nitrogen and carbon isotope concentrations were assessed after a short growth period. Growth conditions had little effect on leaf chemistry and monochromatic green light did not significantly degrade photosynthetic efficiency. This study provides the first evidence to date of positive net ‘green light photosynthesis’ in mosses.     

The Adaptation of Plankton Algae IV. Light Adaptation in Different Algal Species

Two types with regard to adaptation to different light intensities are described: tbe Chlorella type and the Cyclotella type. The Chlorella type is mostly found among the green algae, the Cyclotella type among the diatoms. The Chlorella type adapts to a new light intensity mainly by changing the pigment content. Therefore the cells adapted to a high light intensity have a lower chlorophyll a content per cell than cells adapted to a low light intensity. Light saturation is mostly rather low for cells adapted to low light intensities. The light-saturated rate of photosynthesisist mostly lower for cells adapted to a high light intensity than for cells adapted to a low light intensity. The actual photosynthesis is not much higher at a high light intensity than at a low one. The actual photosynthesis is the photosynthesis at the light intensity where the cells are grown. - The Cyclotella type adapts only by changing the light-saturated rate. The chlorophyll content is the same in cells grown at low and high light intensities. Light saturation for cells grown at a low light intensity is rather high. The light-saturated rate is much higher in the case examined at the high light intensity than at the low one. The actual photosynthesis is considerably higher for cells grown at the high light intensities than for cells grown at low light intensities.- The two adaptation types are not sharply separated since transition types occur.     

THE PHOTOSYNTHETIC EFFICIENCY OF PHYCOCYANIN IN CHROOCOCCUS,AND THE PROBLEM OF CAROTENOID PARTICIPATION IN PHOTOSYNTHESIS

The absorption spectra of the principal pigment components extracted from Chroococcus cells have been measured, and their sum compared with the absorption of a suspension of living cells. The agreement was sufficiently close so that it was concluded the absorption spectra of the extracted and separated pigment components could be used to obtain estimates of the relative absorption of the various components in the living cells. The quantum yield of Chroococcus photosynthesis was measured at a succession of wave lengths throughout the visible spectrum, and the dependence of yield on wave length was compared with the proportions of light absorbed by the pigment components. This comparison showed beyond reasonable doubt that the light absorbed by phycocyanin is utilized in photosynthesis with an efficiency approximately equal to that of the light absorbed by chlorophyll. The light absorbed by the carotenoid pigments of Chroococcus seems for the most part to be unavailable for photosynthesis. The results leave open the possibility that light absorbed by the carotenoids is active in photosynthesis, but with an efficiency considerably lower than that of chlorophyll and phycocyanin. It is also possible that the light absorbed by one or a few of the several carotenoid components is utilized with a high efficiency, while the light absorbed by most of the components is lost for photosynthesis.     

落叶阔叶林冠层光合有效辐射分量的遥感模拟与分析

冠层绿色叶片(光合组分)的光合有效辐射分量(绿色FPAR)真实地反映了植被与外界进行物质和能量交换的能力,获取冠层光合组分吸收的太阳光合有效辐射,对生态系统生产力的遥感估算精度的提高具有重要的意义。研究以落叶阔叶林为例,基于SAIL模型模拟森林冠层光合组分和非光合组分吸收的光合有效辐射,研究冠层FPAR变化规律以及与植被指数的相关关系。结果表明,冠层结构的改变会影响冠层对PAR的吸收能力,冠层绿色FPAR的大小与植被面积指数及光合组分面积比相关;在高覆盖度植被区,冠层绿色FPAR占冠层总FPAR的80%以上,非光合组分的贡献较小,但在低植被覆盖区,当光合组分和非光合组分面积相同时,绿色FPAR不及冠层总FPAR的50%;相比于NDVI,北方落叶阔叶林冠层EVI与绿色FPAR存在更为显著的线性相关关系(R~20.99)。     

Photosynthetic Shutdown in Chlorella NC64A Associated with the Infection Cycle of Paramecium bursaria Chlorella Virus-1

The effects of the algal virus Paramecium bursaria Chlorella virus-1 on the photosynthetic physiology of its host, Chlorella NC64A, was studied by observing changes in Chl fluorescence quenching and O2 exchange. Metabolic changes were calibrated against electron microscopic analysis of the morphological changes that occur during the infection cycle. It takes approximately 10 h from attachment of the virus to final lysis of the host cell, so a complete infection cycle can be observed continuously in one experiment. During the early stages of the infection cycle many rapid changes occurred in the host cell's metabolism and these were reflected in changes of photosynthetic and respiratory rates. The dramatic inhibition of photosynthesis in Chlorella NC64A cells by P. bursaria Chlorella virus-1 has facilitated the use of fluorescence quenching as an accurate measure of the first phase of viral infection (attachment and penetration of the host cell) and the extent to which a population of host cells is infected. Effects of temperature and cation requirement of the infection cycle are described. The relevance of our observations to the events observed during viral infection of higher plants is discussed.     

Photosynthetic efficiency of marine plants

Multicellular marine plants were collected from their natural habitats and the quantum efficiency of their photosynthesis was determined in the laboratory in five narrow wave length bands in the visible spectrum. The results along with estimates of the relative absorption by the various plastid pigments show a fairly uniform efficiency of 0.08 molecules O₂ per absorbed quantum for (a) chlorophyll of one flowering plant, green algae, and brown algae, (b) fucoxanthol and other carotenoids of brown algae, and (c) the phycobilin pigments phycocyanin and phycoerythrin of red algae. The carotenoids of green algae are sometimes less efficient while those of red algae are largely or entirely inactive. Chlorophyll a of red algae is about one-half as efficient (_o2 = 0.04) as either the phycobilins, or the chlorophyll of most other plants. These results as well as those of high intensity and of fluorescence experiments are consistent with a mechanism in which about half the chlorophyll is inactive while the other half is fully active and is an intermediate in phycoerythrin- and phycocyanin-sensitized photosynthesis.     

Vegetation clumping modulates global photosynthesis through adjusting canopy light environment

The spatial dispersion of photoelements within a vegetation canopy, quantified by the clumping index (CI), directly regulates the within-canopy light environment and photosynthesis rate, but is not commonly implemented in terrestrial biosphere models to estimate the ecosystem carbon cycle. A few global CI products have been developed recently with remote sensing measurements, making it possible to examine the global impacts of CI. This study deployed CI in the radiative transfer scheme of the Community Land Model version 5 (CLM5) and used the revised CLM5 to quantitatively evaluate the extent to which CI can affect canopy absorbed radiation and gross primary production (GPP), and for the first time, considering the uncertainty and seasonal variation of CI with multiple remote sensing products. Compared to the results without considering the CI impact, the revised CLM5 estimated that sunlit canopy absorbed up to 9%–15% and 23%–34% less direct and diffuse radiation, respectively, while shaded canopy absorbed 3%–18% more diffuse radiation across different biome types. The CI impacts on canopy light conditions included changes in canopy light absorption, and sunlit–shaded leaf area fraction related to nitrogen distribution and thus the maximum rate of Rubisco carboxylase activity (V_cmax), which together decreased photosynthesis in sunlit canopy by 5.9–7.2 PgC year⁻¹ while enhanced photosynthesis by 6.9–8.2 PgC year⁻¹ in shaded canopy. With higher light use efficiency of shaded leaves, shaded canopy increased photosynthesis compensated and exceeded the lost photosynthesis in sunlit canopy, resulting in 1.0 ± 0.12 PgC year⁻¹ net increase in GPP. The uncertainty of GPP due to the different input CI datasets was much larger than that caused by CI seasonal variations, and was up to 50% of the magnitude of GPP interannual variations in the tropical regions. This study highlights the necessity of considering the impacts of CI and its uncertainty in terrestrial biosphere models.     

Factors Associated with Depression of Photosynthetic Quantum Efficiency in Maize at Low Growth Temperature

The photosynthetic productivity of maize (Zea mays) in temperate regions is often limited by low temperatures. The factors responsible for the sensitivity of photosynthesis in maize to growth at suboptimal temperature were investigated by measuring (a) the quantum yields of CO2 fixation and photosystem II (PSII) photochemistry, (b) the pigments of the xanthophyll cycle, (c) the concentrations of active and inactive PSII reaction centers, and (d) the synthesis of core components of PSII reaction centers. Measurements were made on fully expanded leaves grown at 14[deg]C, both before and during the first 48 h after transfer of these plants to 25[deg]C. Our findings indicate that zeaxanthin-related quenching of absorbed excitation energy at PSII is, quantitatively, the most important factor determining the depressed photosynthetic efficiency in 14[deg]C-grown plants. Despite the photoprotection afforded by zeaxanthin-related quenching of absorbed excitation energy, a significant and more persistent depression of photosynthetic efficiency appears to result from low temperature-induced inhibition of the rate at which damaged PSII centers can be replaced.     

Einfluss verschiedener Lichtwellenlängen auf die Zusammensetzung von Chlorella in Glucosekultur bei gehemmter Photosynthese

Summary Increasing blue light intensity inhibits the growth of Chlorella pyrenoidosa in glucose culture in which photosynthesis is blocked by DCMU, whereas red light supports growth which is the same as or better than that in dark controls.The action spectrum of light induced protein synthesis from exogenous glucose (photosynthesis inhibited, blue light addition resulting in growth >90% of the dark control) shows only one broad maximum at 450–490 nm which resembles the absorption spectrum of carotenoids.     

铀对两种小球藻生长和光合作用的影响

为了探究铀对藻类生长及光合作用的影响,筛选新的基于光合作用的水体铀污染生态风险评价指标,本试验采用不同浓度铀（0、0.5、1、5、10、20mg U·L-1）分别处理普通小球藻(Cholorella vulgaris)和黄龙普通小球藻两种来自不同生境的微藻,在处理后的第3、5、7、10、14d进行相对生长速率、光合放氧速率、叶绿素含量和叶绿素荧光动力学参数等指标的测定。结果表明：（1）0.5mg·L-1低浓度铀处理显著促进两种小球藻的生长和光合作用效率,表现为两种微藻的相对生长速率、光合放氧速率、光系统II最大光化学量子产量Fv/Fm、实际光化学量子产量Y（Ⅱ）、相对电子传递速率rETR等叶绿素荧光参数等指标均显著高于对照, 而5-20 mg·L-1高浓度铀处理则显著抑制两种小球藻的生长和光合作用;（2）黄龙普通小球藻比普通小球藻对铀处理更敏感,在1mg·L-1处理浓度下生长与光合作用就受到显著抑制,可以用来作为水体铀污染生物监测的指示生物;（3）回归分析表明,不同浓度铀处理下,叶绿素荧光参数Y(II)和rETR的响应速度快于相对生长速率、光合放氧速率、叶绿素含量和Fv/Fm等指标的变化,可以作为水体铀污染生态风险评价的敏感指标。     

A heterotrophic synchronous culture of Chlorella

Based on the observation that photoautotrophically grown Chlorella cells fail to complete cell division under anaerobic condition in the dark, we devised a heterotrophic synchronous culture (HSC) system for this green alga. The system consists, at a temperature of 21 degrees C, of a 32 +/- 1 h period under 3% CO2 in air and the successive 12 +/- 1 h period under 0.5% O2 +/- 99.5% N2 (the sum of the two periods is equal to 44 +/- 1 h), using a semi-balanced medium containing glucose in an inorganic salt solution. This procedure could be successively repeated several times and the division index was practically 100%, as it is for Chlorella in the photoautotrophic synchronous culture (PSC). We believe this is the first successful HSC achieved by the method of alternating atmospheric oxygen tension. Synthetic patterns for DNA, RNA and protein as well as chlorophyll during the cell cycle of Chlorella in HSC were similar to those observed in PSC, and the respiratory activity of actively growing cells in HSC was twice that of those in PSC. It is hoped that this system, under the regimen of high and low oxygen tension, can be utilized for other eukaryotic cells.     

武汉市51种园林植物的气体交换特性

对湖北武汉市5个绿地共51种园林植物的气体交换特性的研究表明: 不同绿地间、灌木与乔木间、落叶与常绿植物间的光合能力(A_max)、蒸腾速率(T_r)和光合水分利用效率(PWUE)均有显著差异。绿地间的气体交换特性差异主要表现在物种间, 不同绿地间的小气候或环境差异影响很小。根据51种植物的A_max、T_r和PWUE, 可将它们划分为3大类群。其中大部分植物属于低光合低水分利用型(38种), 其次为高光合高蒸腾型(10种), 低耗水高水分利用型最少, 仅有花榈木(Ormosia henryi)、银木(Cinnamomum septentrionale)和黄心夜合(Michelia bedinieri) 3种。     

Two different strategies for light utilization in photosynthesis in relation to growth and cold acclimation

Seedlings of Lodgepole pine (Pinus contorta L.) and winter wheat (Triticum aestivum L. cv. Monopol) were cold acclimated under controlled conditions to induce frost hardiness. Lodgepole pine responded to cold acclimation by partial inhibition of photosynthesis with an associated partial loss of photosystem II reaction centres, and a reduction in needle chlorophyll content. This was accompanied by a low daily carbon gain, and the development of a high and sustained capacity for non‐photochemical quenching of absorbed light. This sustained dissipation of absorbed light as heat correlated with an increased de‐epoxidation of the xanthophyll cycle pigments forming the quenching forms antheraxanthin and zeaxanthin. In addition, the PsbS protein known to bind chlorophyll and the xanthophyll cycle pigments increased strongly during cold acclimation of pine. In contrast, winter wheat maintained high photosynthetic rates, showed no loss of chlorophyll content per leaf area, and exhibited a high daily carbon gain and a minimal non‐photochemical quenching after cold acclimation. In accordance, cold acclimation of wheat neither increased the de‐epoxidation of the xanthophylls nor the content of the PsbS protein. These different responses of photosynthesis to cold acclimation are correlated with pine, reducing its need for assimilates when entering dormancy associated with termination of primary growth, whereas winter wheat maintains a high need for assimilates as it continues to grow and develop throughout the cold‐acclimation period. It appears that without evolving a sustained ability for controlled dissipation of absorbed light as heat throughout the winter, winter green conifers would not have managed to adapt and establish themselves so successfully in the cold climatic zones of the northern hemisphere.     

The desert green algae Chlorella ohadii thrives at excessively high light intensities by exceptionally enhancing the mechanisms that protect photosynthesis from photoinhibition

Although light is the driving force of photosynthesis, excessive light can be harmful. One of the main processes that limits photosynthesis is photoinhibition, the process of light-induced photodamage. When the absorbed light exceeds the amount that is dissipated by photosynthetic electron flow and other processes, damaging radicals are formed that mostly inactivate photosystem II (PSII). Damaged PSII must be replaced by a newly repaired complex in order to preserve full photosynthetic activity. Chlorella ohadii is a green microalga, isolated from biological desert soil crusts, that thrives under extreme high light and is highly resistant to photoinhibition. Therefore, C. ohadii is an ideal model for studying the molecular mechanisms underlying protection against photoinhibition. Comparison of the thylakoids of C. ohadii cells that were grown under low light versus extreme high light intensities found that the alga employs all three known photoinhibition protection mechanisms: (i) massive reduction of the PSII antenna size; (ii) accumulation of protective carotenoids; and (iii) very rapid repair of photodamaged reaction center proteins. This work elucidated the molecular mechanisms of photoinhibition resistance in one of the most light-tolerant photosynthetic organisms, and shows how photoinhibition protection mechanisms evolved to marginal conditions, enabling photosynthesis-dependent life in severe habitats.     

PHOTOINHIBITION AND RECOVERY AFTER HIGH LIGHT STRESS IN DIFFERENT DEVELOPMENTAL AND LIFE-HISTORY STAGES OF LAMINARIA SACCHARINA (PHAEOPHYTA)1,2

The capacity to cope with high light stress was investigated in different life-history and developmental stages of Laminaria saccharina Lamour. sporophytes and gametophytes. Changes in photosynthetic efficiency and in the level of photoinhibition were measured by in vivo fluorescence changes of photosystem II. Pigment content was studied using high performance liquid chromatography. Additionally, the morphology of the various developmental stages during the life cycle was studied by light microscopy in relation to the photosynthetic parameters. High light stress (2 h, 500 μmol.m-².s^?1) induced photoinhibition of photosynthesis with fast kinetics in older sporophytes and gametophytes. In contrast, the absolute degree of photoinhibition after light stress was higher in younger than in older sporophytes. Photosynthesis recovered faster in older sporophytes and gametophytes compared to young sporophytes. In very young sporophytes, photosynthesis did not recover fully even after 12 h exposure to low light, indicating severe photodamage. Kinetics of recovery in old sporophytes and in gametophytes showed a fast and a slow phase, whereas younger sporophytes recovered only with a slow phase, The fast phase is indicative of a decline of the photoprotective process, whereas the slow phase indicates a recovery from photodamage. The capacity to cope with high light stress in Laminaria sporophytes increased with increasing age of the thalli. The gametophytes are less sensitive to high light stress and may be selected to endure unfavorable white light conditions. Investigation of the xanthophylls showed that the higher resistance to high light is not caused solely by a higher content of xanthophyll cycle pigments. Additionally, changes in the thallus structure during the development of the sporophytes seemed to cause a higher resistance to high light. The observed changes in the ability to cope with high light in the different life-history and developmental stages of Laminaria saccharina may influence the distribution of the species on the shore.     

Photosynthetic action spectra of marine algae

A polarographic oxygen determination, with tissue in direct contact with a stationary platinum electrode, has been used to measure the photosynthetic response of marine algae. These were exposed to monochromatic light, of equal energy, at some 35 points through the visible spectrum (derived from a monochromator). Ulva and Monostroma (green algae) show action spectra which correspond very closely to their absorption spectra. Coilodesme (a brown alga) shows almost as good correspondence, including the spectral region absorbed by the carotenoid, fucoxanthin. In green and brown algae, light absorbed by both chlorophyll and carotenoids seems photosynthetically effective, although some inactive absorption by carotenoids is indicated. Action spectra for a wide variety of red algae, however, show marked deviations from their corresponding absorption spectra. The photosynthetic rates are high in the spectral regions absorbed by the water-soluble "phycobilin" pigments (phycoerythrin and phycocyanin), while the light absorbed by chlorophyll and carotenoids is poorly utilized for oxygen production. In red algae containing chiefly phycoerythrin, the action spectrum closely resembles that of the water-extracted pigment, with peaks corresponding to its absorption maxima (495, 540, and 565 mµ). Such algae include Delesseria, Schizymenia, and Porphyrella. In the genus Porphyra, there is a series P. nereocystis, P. naiadum, and P. perforata, with increasingly more phycocyanin and less phycoerythrin: the action spectra reflect this, with increasing activity in the orange-red region (600 to 640 mµ) where phycocyanin absorbs. In all these red algae, photosynthesis is almost minimal at 435 mµ and 675 mµ, where chlorophyll shows maximum absorption. Although the chlorophylls (and carotenoids) are present in quantities comparable to the green algae, their function is apparently not that of a primary light absorber; this role is taken over by the phycobilins. In this respect the red algae (Rhodophyta) appear unique among photosynthetic plants.     

The Influence of Cu on Photosynthesis and Growth in Diatoms

Cu in ionic form in a balanced medium affects the rate of photosynthesis and growth in the diatom Nitzschia palea in about the same way as in the green alga Chlorella pyrenoidosa. Remarkable differences are found, however. Small concentrations of Cu influence the rate of photosynthesis considerably more in the diatom than in the green alga whereas the opposite is the case concerning growth. The latter is most likely a consequence of excretion of organic matter by the diatom in presence of Cu whereas this does not take place in Chlorella. Some of the excreted organic matter may bind Cu and thus make the medium suitable for growth. Although pre-treatment with Cu in the dark has no influence on the subsequent rate of photosynthesis in the light, organic matter is excreted in the dark immediately after the addition of Cu. The influence of Cu on the rate of photosynthesis varies by a factor of about 30 according to the stage of growth in a synchronized culture.     

Photosynthetic Efficiency in Lawson's Bay on the East Coast of India

Seasonal variations in the efficiency of utilization of radiant energy by phytoplankton photosynthesis in a tropical embayment followed the same pattern as that of primary production. showing that incident radiation did not limit phytoplankton production. Peak values in primary production and photosynthetic efficiency coincided with periods of nutrient enrichment caused either by upwelling during the southwest monsoon or by run-off during the northeast, monsoon. A world-wide comparison of published data on photosynthetic efficiencies in different latitudes showed that higher efficiency is achieved in the tropics, where the values are similar to those observed on phytoplankton cultures. Based on the maximum efficiency of photosynthesis attained, three regimes can be recognized in tropical waters: 1) regions of upwelling with a maximum of 6%,. 2) coastal bays with 0.7%, 3) oceanic regions with 0.24%.