Primary Photosynthetic Processes Research Articles

A universal method for the isolation of photochemically active broken chloroplasts from conifer needles and its possible application in photosynthetic studies

We have developed a simple and an effective method for the isolation of photochemically active broken chloroplasts from conifer needles that can be applied for a wide variety of conifer species with needle-like leaves. The utilisation of this method in photosynthetic studies offers a possibility to examine the efficiency of almost any component of thylakoid electron-transport chain and to disclose information about individual parts of primary photosynthetic processes that would be otherwise difficult to obtain. Various aspects influencing the outcome of this procedure, including the amount of needles necessary for sufficient yields, the possible length and the conditions of their storage, the best method for their disruption, the composition and pH of isolation and storage buffers, the centrifugation sequence, etc., are discussed.

Effect of water stress on leaf photosynthesis, chlorophyll content, and growth of oriental lily

The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to increasing water stress were analyzed based on the net photosynthetic rate (P n), stomatal conductance (g s), intercellular CO2 concentration (Ci), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (Ls) in the Horqin Sandy Land of western China. A photosynthesis-PAR response curve was constructed to obtain light-compensation and light-saturation points (LCP and LSP), the maximum photosynthetic rates (P max) and dark respiration rates (R D). The growth of lilies in the pots was analyzed after anthesis. Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied. The results indicated that drought stress not only significantly decreased P n, E, g s, photosynthetic pigment content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (P n)-PAR response curve. Drought stress increased LCP and R D and decreased LSP and P max. There were both stomatal and nonstomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and affected the diurnal pattern of gas exchange and P n-PAR response curves, thereby reducing plant quality (lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin Sandy Land.

Freezing cytorrhysis and critical temperature thresholds for photosystem II in the peat moss Sphagnum capillifolium

Leaflets of Sphagnum capillifolium were exposed to temperatures from -5 degrees C to +60 degrees C under controlled conditions while mounted on a microscope stage. The resultant cytological response to these temperature treatments was successfully monitored using a light and fluorescence microscope. In addition to the observable cytological changes during freezing cytorrhysis and heat exposure on the leaflets, the concomitant critical temperature thresholds for inactivation of photosystem II (PS II) were studied using a micro fibre optic and a chlorophyll fluorometer mounted to the microscope stage. Chlorophyllous cells of S. capillifolium showed extended freezing cytorrhysis immediately after ice nucleation at -1.1 degrees C in the water in which the leaflets were submersed during the measurement. The occurrence of freezing cytorrhysis, which was visually manifested by cell shrinkage, was highly dynamic and was completed within 2 s. A total reduction of the mean projected diameter of the chloroplast containing area during freezing cytorrhysis from 8.9 to 3.8 microm indicates a cell volume reduction of approximately -82%. Simultaneous measurement of chlorophyll fluorescence of PS II was possible even through the frozen water in which the leaf samples were submersed. Freezing cytorrhysis was accompanied by a sudden rise of basic chlorophyll fluorescence. The critical freezing temperature threshold of PS II was identical to the ice nucleation temperature (-1.1 degrees C). This is significantly above the temperature threshold at which frost damage to S. capillifolium leaflets occurs (-16.1 degrees C; LT(50)) which is higher than observed in most higher plants from the European Alps during summer. High temperature thresholds of PS II were 44.5 degrees C which is significantly below the heat tolerance of chlorophyllous cells (49.9 degrees C; LT(50)). It is demonstrated that light and fluorescence microscopic techniques combined with simultaneous chlorophyll fluorescence measurements may act as a useful tool to study heat, low temperature, and ice-encasement effects on the cellular structure and primary photosynthetic processes of intact leaf tissues.

Hydrogen photoproduction by use of photosynthetic organisms and biomimetic systems

Hydrogen can be important clean fuel for future. Among different technologies for hydrogen production, oxygenic natural and artificial photosyntheses using direct photochemistry in synthetic complexes have a great potential to produce hydrogen, since both use clean and cheap sources: water and solar energy. Artificial photosynthesis is one way to produce hydrogen from water using sunlight by employing biomimetic complexes. However, splitting of water into protons and oxygen is energetically demanding and chemically difficult. In oxygenic photosynthetic microorganisms such as algae and cyanobacteria, water is split into electrons and protons, which during primary photosynthetic process are redirected by photosynthetic electron transport chain, and ferredoxin, to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, e- and H+ recombine and form gaseous hydrogen. Biohydrogen activity of hydrogenase can be very high but it is extremely sensitive to photosynthetic O2. In contrast, nitrogenase is insensitive to O2, but has lower activity. At the moment, the efficiency of biohydrogen production is low. However, theoretical expectations suggest that the rates of photon conversion efficiency for H2 bioproduction can be high enough (>10%). Our review examines the main pathways of H2 photoproduction by using of photosynthetic organisms and biomimetic photosynthetic systems.

Mathematical and computer modeling of primary photosynthetic processes

We review the recent research on kinetic and direct multiparticle modeling of the processes in the photosynthetic membrane conducted at the Chair of Biophysics of the Biological Faculty, Moscow State University. The models take into account the modern experimental data on the heterogeneous structure and the kinetic characteristics of the system. The generalized kinetic model describes the processes in multisubunit complexes (photosystems I and II, the cytochrome complex), the coupled transmembrane ion fluxes and generation of the electrical and electrochemical potentials. Identification of the model parameters allows estimation of the rate constants for reactions that cannot be examined experimentally. Multiparticle models provide a vivid picture of the interaction between the electron transport chain components in the thylakoid lumen and stroma, and explicitly represent Brownian diffusion and electrostatic interactions between electron carriers. Combination of different description methods (differential equations and the Brownian dynamics formalism) makes it possible to model, in the complicated 3D environment of the plant cell, the processes that in the aggregate ensure the high efficacy of energy transduction in photosynthesis.

Fluoranthene influences endogenous abscisic acid level and primary photosynthetic processes in pea (Pisum sativum L.) plants in vitro

The influence of increasing concentrations (0.1, 1.0 and 5.0 mg l−1) of fluoranthene (FLT) on growth, endogenous abscisic acid (ABA) level and primary photosynthetic processes in 21-day-old pea plants (Pisum sativum L.) in vitro was investigated. Murashige and Skoog’s (MS) medium, with or without FLT, was enriched with indole-3-acetic acid (IAA; 0.1 mg l−1) or a combination of IAA (0.1 mg l−1) plus N6-benzyladenine (BA; 0.1 mg l−1). The level of endogenous ABA significantly increased with increasing FLT concentrations in the presence of both IAA and IAA plus BA. An increased level of endogenous ABA was observed in plants treated with IAA alone. The growth of shoot, callus and the content of photosynthetic pigments (chlorophyll a and b, carotenoids), in both IAA- and IAA plus BA-treated plants, were significantly stimulated by FLT at its lowest concentration (0.1 mg l−1) assayed in this study. However, FLT at higher concentrations (1.0 and 5.0 mg l−1) significantly inhibited all these parameters. Chlorophyll fluorescence imaging showed that FLT only at the highest concentration (5.0 mg l−1) in the presence of IAA (0.1 mg l−1) significantly increased F0, but decreased FV/FM and ΦII.

Duration of irradiation rather than quantity and frequency of high irradiance inhibits photosynthetic processes in the lichen Lasallia pustulata

Lichen thalli were exposed to 4 regimes differing in irradiance and duration of irradiation. Photosynthetic efficiency of thalli was monitored by chlorophyll fluorescence parameters and xanthophyll cycle analysis. Maximal quantum yield of photosystem 2 (FV/FM) decreased gradually with time in long-term treatment. The effect of additional short-term high irradiance (HI) treatment applied each 24 h was not significant. Nevertheless, short-term HI applied repeatedly on thalli kept in the dark led to a significant decrease of FV/FM. Non-photochemical quenching recorded during the long-term treatment corresponded to the content of zeaxanthin (Z). In short-term treatment, however, proportion of Z (and antheraxanthin) to total amount of xanthophyll cycle pigments recovered to the initial values every 24 h after each repeated short-term HI event in thalli kept in dark. Thus duration of irradiation rather than irradiance and frequency of HI events is important for a decrease in primary photosynthetic processes in wet thalli of Lasallia pustulata. Rapidly responding photoprotective mechanisms, such as conversion of xanthophyll cycle pigments, are involved mainly in short-term irradiation events, even at HI.

Low-temperature limitation of primary photosynthetic processes in Antarctic lichens Umbilicaria antarctica and Xanthoria elegans

Temperature response curves of chlorophyll a fluorescence parameters were used to assess minimum sub-zero temperature assuring functioning of photosynthetic photochemical processes in photosystem II (PS II) of Antarctic lichens. Umbilicaria Antarctica and Xanthoria elegans were measured within the temperature range from −20 to +10°C by a fluorometric imaging system. For potential (FV/FM) and actual (ΦII) quantum yields of photochemical processes the minimum temperature was found to be between −10 and −20°C. Non-photochemical quenching (NPQ) of absorbed excitation energy increased with temperature drop reaching maximum NPQ at −15°C. Image analysis revealed intrathalline heterogeneity of chlorophyll a fluorescence parameters with temperature drop. Temperature response of ΦII exhibited an S-curve with pronounced intrathalline differences in X. elegans. The same relation was linear with only limited intrathalline difference in U. antarctica. The results showed that Antarctic lichen species were well adapted to sub-zero temperatures and capable of performing primary photosynthesis at −15°C.

Effects of methanol on photosynthetic processes and growth of Lemna gibba.

Effects of methanol on growth and photosynthetic activity of Lemna gibba exposed under continuous illumination were examined. As a higher plant, L. gibba appeared to be much more sensitive to methanol inhibitory effect compared with some algae (Theodoridou et al. [2002] Biochim. Biophys. Acta, 1573, 189-198). We found that stimulatory or inhibitory effects were strongly dependent on the methanol concentration and the time of exposure. When the exposure was up to 0.2% methanol, the growth rate of biomass was improved by 50%. However, stimulatory effect of methanol appeared to be smaller when plants were exposed for 48 h compared with 24 h. Increase in biomass induced by methanol was not based on the increase in primary photosynthetic process but rather on accommodation of energy dissipation during photosynthesis. Inhibitory effect on the growth of L. gibba already observed for 0.5% methanol was strongly associated with the increase in the nonphotochemical energy dissipation. The ratio between biomass and methanol concentration appeared to determine the stimulatory or the inhibitory effect. Suggested explanations for the stimulatory and the inhibitory effects are presented.

Low temperature spectroscopy and hole-burning study of iron-stress induced chlorophyll protein CP 34 of Synechococcus elongatus

Numerous autotrophic organisms alter the composition and function of their photosynthetic apparatus under external stress conditions. This is also the case of the cyanobacterial response to iron deprivation that includes (besides other changes) the synthesis of a new, iron-stress induced chlorophyll binding protein. The aim of this contribution is the spectroscopic characterization of such complex designated CP 34* and isolated from the iron-stressed cells of the thermophilic cyanobacterium Synechococcus elongatus. The study is focused on the ultrafast primary photosynthetic processes assessed by means of low temperature and hole-burning spectroscopy. These techniques allowed us to obtain the exciton relaxation times in the complex and to determine the strength of pigment-protein interaction. Also the site distribution function acquired from the burned holes depth is shown.

Low-temperature absorption off-resonant hole-burning spectroscopy of pheophytine a in photosystem II reaction center

Chlorophylls, pheophytines and carotenes are main photosynthetic pigments. They play a crucial role in primary photosynthetic processes (excited energy transfer and electron transport). In this contribution we report on both resonant and off-resonant hole-burning low-temperature absorption spectra. The resonant narrow zero-phonon holes together with broad (≈84 cm −1) off-resonant holes were burnt into Q y absorption bands, while very broad (≈250 cm −1) off-resonant satellite holes were observed in Q x absorption transitions. This technique enabled one to distinguish between satellite holes of chlorophyll a and pheophytine a and consequently to localize spectral bands of both pheophytines a in the complex Q y absorption spectrum of reaction center of photosystem II containing six chlorophylls a, two pheophytines a and one β-carotene.

Reaction center and antenna processes in photosynthesis at low temperature

Around 1960 experiments of Arnold and Clayton, Chance and Nishimura and Calvin and coworkers demonstrated that the primary photosynthetic electron transfer processes are not abolished by cooling to cryogenic temperatures. After a brief historical introduction, this review discusses some aspects of electron transfer in bacterial reaction centers and of optical spectroscopy of photosynthetic systems with emphasis on low-temperature experiments.

Time-resolved spectroscopy of the primary photosynthetic processes of membrane-bound reaction centers from an antenna-deficient mutant of Rhodobacter capsulatus

The primary photosynthetic reactions in whole membranes of the antenna-deficient mutant strain U43 (pTXA6–10) of Rhodobacter capsulatus are studied by transient absorption and emission spectroscopy with subpicosecond time resolution. Extensive similarities between the transient absorption data on whole membranes and on isolated reaction centers support the idea that the primary processes in isolated reaction centers are not modified by the isolation procedure.

Laser-induced optoacoustic calorimetry of cyanobacteria. The efficiency of primary photosynthetic processes in state 1 and state 2

The heat released by all primary processes of photosynthesis within 2 μs of a laser flash was measured by optoacoustic spectroscopy of the cyanobacteria Synechococcus sp. PCC 6301 adapted to state 1 and state 2. Heat production was compared between intact cells with open and closed reaction centres allowing direct determination of the efficiency of photosynthetic energy storage. The fraction of absorbed energy released as heat was the same for cells in state 1 and state 2 for excitation of either phycocyanin or chlorophyll a. We conclude that the efficiency of excitation energy transfer and primary photochemical energy storage was not affected by the state transition. These results contradict proposed models for the state transition in cyanobacteria, which involve the uncoupling of phycobilin pigments from energy transfer to chlorophyll a.

Interrelationship between Salt and Light Stress on Primary Processes of Photosynthesis

Summary Influence of salt stress and its interaction with light stress on primary photosynthetic processes were investigated in wheat (Triticum aestivum L. var. HD 2329). Salt stress by itself had no significant effect on electron transport activity and Fv/Fm ratio suggesting that the efficiency of the photochemistry of PSII is not affected. Decrease in Fm due to salt stress may influence reduction of QA Our results on fluorescence indicate that salt stress predisposes photoinhibition of plants and also reduces its ability to recover from photoinhibition.

Effect of specific mutations of tyrosine-(M)210 on the primary photosynthetic electron-transfer process in Rhodobacter sphaeroides.

We have measured the rate of the initial electron-transfer process as a function of temperature in reaction centers in a native strain of the photosynthetic bacterium Rhodobacter sphaeroides and two mutants generated by site-directed mutagenesis. In the mutants, a tyrosine residue in the vicinity of the primary electron donor and acceptor molecules was replaced by either phenylalanine or isoleucine. The electron-transfer reaction is slower in the mutants and has a qualitatively different dependence on temperature. In native reaction centers the rate increases as the temperature is reduced, in the phenylalanine mutant it is virtually independent of temperature, and in the isoleucine mutant it decreases with decreasing temperature. At 77 K, the electron-transfer reaction is approximately 30 times slower in the isoleucine mutant than in the native. These observations support the view that tyrosine-(M)210 plays an important role in the electron-transfer mechanism. In the isoleucine mutant at low temperatures, the stimulated emission from the excited reaction center undergoes a time-dependent shift to shorter wavelengths.

Chilling Injury in Mature Leaves of Rice. II. Varietal Differences in the Response to Interactions Between Low Temperature and Light Measured by Chlorophyll Fluorescence at 77k and the Quantum Yield of Photosynthesis

Characteristics of photosynthetic CO2 exchange and 77K chlorophyll fluorescence in attached and detached leaves of rice were used to examine differences between five varieties exposed to a combination of bright light and low temperature. Preliminary studies established that attached leaves of varieties did not differ in the light dependence of photosynthesis at CO2 saturation or fluorescence properties when grown in full sunlight and measured under comparable conditions. All varieties showed a depression in maximum photosynthetic rate, but not in quantum yield or chlorophyll fluorescence when examined in the late afternoon after a period of active photosynthesis in air at 25°C. Attached leaves of all varieties showed depression of the maximum rate of photosynthesis and of quantum yield as well as an increase in Fo and a decrease in Fv/Fm of chlorophyll fluorescence at 77K following horizontal exposure to bright light in air at 25°. Similar results were obtained with detached leaves exposed to bright light while floating on water at 25°C. The rate of photosynthetic CO2 fixation in air as a function of temperature was examined in attached leaves of two representative varieties, Japonica-like cv. Hungarian- 1, and Indica-derived cv. IR-8. The former was capable to rates of photosynthesis at 10°C which were twice those of the latter, although the rates at 25°C were similar in both varieties. When detached leaves of five varieties of rice were floated on water at 10°C while exposed to 700 �mol photons m-2 s-1 of white light, consistent differences in the response of quantum yield, light and CO2 saturated O2 evolion and 77K fluorescence properties were found. Exposure to bright light at low temperature exaggerated the effects of bright light on these parameters, and larger effects were found in the Indica-derived varieties than in Japonica-like cv. Hungarian-1. These treatments at 10°C did not influence the extent of increase in Fo, but led to a greater decline in Fv/Fm of 77K chlorophyll fluorescence compared with treatments at 25°C. Varieties in which there was a larger decline in Fv/Fm showed slower recovery of variable fluorescence in the dark at 25°C, and especially at 10°C. These responses to in vitro treatments seem capable of distinguishing varieties such as cvv. Hungarian-1 and Er Bai Ai, which are believed to be more chilling tolerant by other criteria, from chilling sensitive varieties such as Gui Chao-2 and IR-8. Even though there is potential for application of these methods in screening programs, there is little evidence that the lesions in primary photosynthetic processes indicated by these methods are significant determinants of photosynthesis under field conditions.

Primary photosynthetic processes in Heliobacterium chlorum at 15K

Absorbance changes induced by 25-ps laser flashes were measured in membranes of Heliobacterium chlorum at 15 K. Absorbance difference spectra, measured at various times after the flash showed negative bands in the Qy region at 812, 793 and 665 nm. The first of these bands was attributed to the formation of excited singlet states of a long-wavelength form of antenna bacteriochlorophyll g (BChl g 808). Absorbance changes of shorter wavelength absorbing antenna BChls g were at least an order of magnitude smaller, indicating rapid excitation energy transfer (i.e. within the time resolution of the apparatus) from these BChls to BChl g 808. Excited BChl g 808 showed a bi-exponential decay with time constants of 50 and 200 ps. The bands at 793 and 665 nm may be attributed to the primary charge separation and reflect the photooxidation of the primary electron donor P-798 and photoreduction of a primary electron acceptor absorbing near 670 nm, presumably a BChl c or Chl a-like pigment. The bleaching of this pigment reversed with a time constant of 300 ps at 15 K and of 800 ps at 300 K. This indicates that electron transfer from the primary to the secondary electron acceptor is approximately 2.5 times faster at 15 K than at room temperature.

Chilling Injury in Mature Leaves of Rice. I. Varietal Differences in the Effects of Chilling on Canopy Photosynthesis Under Simulated 'Dry Cold Dew Wind' Conditions Experienced in South-East China

Canopy temperature and incident photosynthetically active radiation were measured in experimental rice plots in Guangzhou, South China, during conditions which approximated those of the 'dry cold dew wind', a chilling phenomenon which is responsible for substantial yield reduction in rice. These field conditions were then reproduced in controlled environment photosynthetic measurement chambers. Mature plants of five varieties of rice were arranged to simulate a canopy in these chambers which was then exposed to a 3-day chilling treatment (21°C day/10°C night) 14 days after anthesis. Canopy photosynthesis was measured before, during and after the chilling period. A Japonica-like cultivar, Hungarian-1 from Central Europe, and an Indica-like cultivar, Lemont from Texas, were markedly less sensitive to a chilling-dependent reduction in photosynthesis than were cultivars Gui Chao-2, Er Bai Ai and IR-8 from South-East China and The Philippines. The extent of chilling-dependent reduction in photosynthesis was greater if roots of plants in the simulated canopy were allowed to track air tempera- ture at night. This led to a 5-7°C differential between root and air temperature in the morning and was associated with a midday depression of photosynthesis in all varieties. If root temperature was kept at 20°C during the day and night and air temperature controlled at 21°C day/ 10°C night, the effects of chilling on photosynthesis were much less pronounced. These changes in canopy photosynthesis following chilling treatments were correlated with changes in leaf level parameters. The level of soluble sugars and starch in leaves was found to remain high during the first cool night and to increase further during the next day. In cultivars which showed pronounced inhibition of canopy photosynthesis throughout the chilling treatment (Gui Chao-2, IR-8), soluble sugars remained at high levels until temperatures were returned to control values. In the less sensitive cultivar, Hungarian-1, soluble sugars declined throughout the chilling treatment. These results suggest inhibition of photosynthesis may be associated with sugar retention in leaves of rice at low temperatures, and imply differences between cultivars in this response. Other photosynthetic parameters monitored included the maximum rate of light and CO2 saturated photosynthesis, the quantum yield of photosynthesis, and Fo and Fv/Fm of chlorophyll fluorescence at 77K. Surprisingly, Hungarian-1, the cultivar which showed least impairment of canopy photosynthesis showed greater reduction in quantum yield and larger changes in fluorescence parameters during the chilling treatments. These changes were readily reversible and may be related to the more horizontal leaf habit of this cultivar compared with the more vertical orientation of leaves in the other cultivars. These observations imply that assimilate regulation of photosynthetic metabolism, rather than light dependent damage to primary photosynthetic processes, underlies low temperature effects on yield of rice during grain filling.

Effects of Deep Dormancy on the Primary Processes of Photosynthesis in Vine (Vitis vinifera) Shoots

Summary The primary processes of photosynthesis in bark phelloderm of one-year-old vine shoots were investigated by means of the delayed fluorescence method. All of the processes investigated (electron transport and oxygen-evolving activity as well as energization of membranes) in the bark phelloderm were shown to take place at a lower level of activity in comparison with the leaves. A further inactivation of the primary photosynthetic processes in the bark phelloderm is observed in the period of deep dormancy whereas after the end of this period a gradual reactivation of the processes takes place. An express method for determination of the beginning and the end of deep dormancy in vine shoots is proposed.