Changes in the photosynthetic apparatus of maize in response to simulated natural temperature fluctuations

The response of the photosynthetic apparatus to low temperature periods differed among three hybrids of maize (Zea mays L.) grown in a phytotron. Light-saturated photosynthetic rates, leaf chlorophyll content, and mesophyll cell photosynthetic unit density all declined with increasing duration of low temperature. No single metabolic or physiological parameter appeared to control the response of the three hybrids to low temperature stress. Among all temperature treatments, net photosynthetic rate on a leaf area basis was more closely correlated with leaf chlorophyll content than with any other measured parameter. Final shoot dry weight was most highly correlated with stomatal conductance to CO₂.     

The ontogenetic approach to chlorophyll fluorescence studies of plant photosynthetic apparatus under stressful conditions

Based on the analysis of reasons limiting the application of the method of chlorophyll fluorescence induction for estimating the state of the leaf photosynthetic apparatus under prolonged stress, the necessity of the ontogenetic approach consisting in a more exact determination of leaf age was substantiated. A comparison of the calendar and ontogenetic ways of determination of age of cucumber leaves under controlled conditions revealed essential distinctions in the estimation of plant leaf photosynthetic apparatus by the method of chlorophyll fluorescence induction for two variants distinguishing by the cultivation light regime ("white", 400-700 nm, and "red", 600-700 nm). It was shown that, in the case of prolonged effect of the stress factor on the plant, the unambiguity of the interpretation of chlorophyll fluorescence induction parameters in the estimation of the state of their photosynthetic apparatus depends essentially on the choice of the ontogenetic period of leaves of plants being compared and the accuracy of determination of leaf age.     

The usefulness of the chlorophyll fluorescence parameters in harvest prediction in 10 genotypes of winter triticale under optimal growth conditions

The aim of the experiment was to detect differences in the activity of the photosynthetic apparatus in 10 genotypes of winter triticale. Measurements of gas exchange and chlorophyll fluorescence were performed. Among the tested genotypes, the photosynthetic apparatus of Timbo and Piano was the most active, while the photosynthesis of both Babor and Boreas was highly reduced. Additionally, we have found significant correlations between the yield and some parameters of chlorophyll fluorescence and leaf gas exchange. Parameters of chlorophyll fluorescence are useful for estimation of the functional state of the photosynthetic apparatus and could become selection criteria in plant breeding. Moreover, such parameters permit definition of the effectiveness of the utilization of chlorophyll a excitation energy and co‐operation of the light phase reactions, with reactions occurring during the dark phase of photosynthesis.     

Examination of chlorophyll fluorescence in sulfur-deprived cells of <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis>

Pulse amplitude modulation fluorimetry was used to assess chlorophyll fluorescence parameters in Chlamydomonas reinhardtii cells during sulfur deprivation. A significant (fourfold) increase in the chlorophyll fluorescence yield (parameters F ₀ and F _m) normalized to the chlorophyll concentration was shown for deprived cells. The chlorophyll content did not change during the deprivation experiments. An analysis of nonphotochemical quenching of chlorophyll fluorescence indicated a considerable modification of the energy deactivation pathways in photosystem II (PSII) of sulfur-deprived cells. For example, starved cells exhibited a less pronounced pH-dependent quenching of excited states and a higher thermal dissipation of excess light energy in the reaction centers of PSII. It was also shown that the photosynthetic apparatus of starved cells is primarily in state 2 and that back transition to state 1 is suppressed. However, these changes cannot cause the discovered elevation of chlorophyll fluorescence intensity (F ₀ and F _m) in the cells under sulfur limitation. The observed increase in the chlorophyll fluorescence intensity under sulfur deprivation may be due to partial dissociation of peripheral light-harvesting complexes from the reaction centers of PSII or a malfunction of the dissipative cycle in PSII, involving cytochrome b ₅₅₉.     

Discrete character of the development of the photosynthetic apparatus in greening barley leaves

Biogenesis of the photosynthetic apparatus in greening etiolated leaves of barley (Hordeum vulgare L) was investigated by an approach permitting investigation of this process under conditions that minimize differences in plastid development. Distributions of barley leaves greening for 24 h as to chlorophyll content and of chloroplast grana as to number of thylakoids were shown to be of a multimodal character. The shape of time-course curves of chlorophyll accumulation in local sites of greening etiolated leaves was of a stepped or (at the end of greening) undulated character. The stepwise accumulation of chlorophyll was accompanied by wave-like changes in chlorophyll b/a ratio, intensity of low-temperature chlorophyll fluorescence and photosynthetic activity with minima at the time points of transition to accelerated chlorophyll accumulation. It is assumed that (1) development of the photosynthetic apparatus in local sites of greening etiolated leaves occurs stepwise, from one steady level to another, but not as gradually as is generally accepted, and (2) every separate step in development of the photosynthetic apparatus seems to begin with formation of photosystem cores and to end with the synthesis of light-harvesting complexes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Spectroscopy of the peridinin-chlorophyll-a protein: insight into light-harvesting strategy of marine algae

An important component of the photosynthetic apparatus is a light-harvesting system that captures light energy and transfers it efficiently to the reaction center. Depending on environmental conditions, photosynthetic antennae have adopted various strategies for this function. Peridinin-chlorophyll-a protein (PCP) represents a unique situation because, unlike other antenna systems which have a preponderance of chlorophyll, it has the carotenoid, peridinin, as its major pigment. The key structural feature of peridinin is a conjugated carbonyl group. Owing to the presence of this group, an intramolecular charge-transfer excited state is formed in peridinin which exhibits different excited state spectra and dynamics depending on the polarity of the environment. The charge-transfer state also facilitates energy transfer between peridinin and chlorophyll-a in PCP. This review summarizes results of spectroscopic investigations of PCP in the past few years, emphasizing the specific light-harvesting strategy developed by marine photosynthetic organisms utilizing carbonyl-containing carotenoids in their antenna complexes.     

Capture frequency of excitations and energy transfer between photosynthetic units in the photosystem II

The connections which exist, in the photosynthetic apparatus, between the spatial arrangement of chlorophyll and the movement of excitation energy are discussed.The capture frequency of excitations in the photosystem II is analysed. At the microscopic level of a photosynthetic unit two stages are studied: the propagation of the excitation to the reaction centre and the photochemical utilization of the excitation by the centre. It is shown that the transport process is not a limiting one. It implies that the capture frequency depends on the reaction centre state. Thus it is possible to distinguish eight states for a photosynthetic unit of system II.At the macroscopic level of a set of units, the analysis of the fluorescence yield-fluctuations shows that these units are not isolated. It also indicates that the fluorescence emitted by the photosynthetic apparatus originates almost entirely from the system II, and that the reaction centres are traps for excitations whatever their states.     

Acclimation of<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis> to the light environment: the relationship between photosynthetic function and chloroplast composition

Plants respond to growth under different environmental conditions by adjusting the composition of the photosynthetic apparatus. To investigate the consequences of the acclimation strategies adopted by Arabidopsis thaliana, we have assessed the functioning of the photosynthetic apparatus in plants with very different chloroplast compositions. Using chlorophyll fluorescence analysis, we have determined the efficiency of, and capacity for, electron transport, assessed the ability to undergo state transitions, and measured non-photochemical quenching over a range of actinic irradiances followed by its resolution into fast- and slow-relaxing components; parallel measurements of leaf carotenoid composition were also carried out. The data clearly show that acclimation serves to maintain the electron transport chain in an oxidised state, ensuring efficient photochemistry. Furthermore, plants grown in high light have a greater capacity for energy-dependent feedback de-excitation, but this is not correlated with xanthophyll cycle pigment levels or de-epoxidation state. Surprisingly, even plants with very low levels of light-harvesting complexes were able to undergo state transitions. We also show that apparent discrepancies between chloroplast composition and photosynthetic function can be attributed to varying degrees of light penetration through the leaf. Thus, leaf chlorophyll content is an important factor influencing acclimation within the leaf.     

Characteristics of the leaf photosynthetic machinery in broad bean grown in zinc chloride aqueous solutions

The structural and functional characteristics of bean leaves (the content of chlorophyll, the rate of oxygen production, the slow fluorescence induction, and light-induced changes in the EPR signal I from oxidized reaction centers P700+) were investigated to obtain insight into the mechanism of influence of zinc chloride on the photosynthetic apparatus. Seedlings were grown on hydroponic medium containing ZnCl2 at concentrations from 10(-7) to 10(-3) M. At low concentrations of ZnCl2, a decrease in the content of chlorophyll per one unit of leaf mass was observed, while the rate of oxygen production per chlorophyll was increased. High concentrations of ZnCl2 in the hydroponic medium caused the slowed down the plant development and inhibited the light-induced production of oxygen. The changes in biophysical characteristics of leaves the parameter FM/FT of the slow fluorescence induction, and kinetics of redox transients of P700 induced by ZnCl2 were of similar character and correlated with the changes in photosynthetic activity. The data obtained demonstrate that structural and functional changes in the photosynthetic apparatus induced by the variations of growth conditions have adaptive character.     

快速叶绿素荧光诱导动力学分析在光合作用研究中的应用

JIP-测定(JIP-test)是以生物膜能量流动为基础建立的分析方法.利用该方法可以获得有关光系统Ⅱ的大量信息.文章介绍了快速叶绿素荧光诱导动力学曲线的定义、数据分析方法及相关参数的意义,并举例说明如何利用该方法分析不同环境条件对光合机构主要是PSⅡ的供体侧、受体侧及PSⅡ反应中心的影响.     

Structural and functional characteristics of photosynthetic apparatus of chlorophyll-containing grape vine tissue

Photosynthesis in tissues under periderm of woody stems and shoots of perennial plants occurs in environment that is very different from the internal environment of leaf chloroplasts. These tissues are characterized by high CO₂ and low O₂ concentrations, more acidic surroundings, besides that only light which have passed through periderm reaches photosynthetic antennas. In contrast to leaves of deciduous plants chlorenchyma tissues of wintering plant organs are exposed to temperature fluctuations during all seasons, that is why the photosynthetic apparatus of woody stems has to be able to adapt to a wide range of environmental temperatures. In order to reveal unique features, which enable photosynthetic apparatus of chlorenchyma cells in woody plant organs to implement biological functions under different light and temperature conditions, we studied photosynthetic tissues of stem cortex in grapevine (Vitis vinifera L.) under normal conditions and after exposure to suboptimal temperatures and high light intensity. Comparative analysis of photosynthetic pigment composition and low-temperature chlorophyll fluorescence emission spectrum of leaves, young shoots and chlorenchyma of lignified shoots revealed relatively high level of chlorophyll b and carotenoids, and high photosystem II (PSII) to photosystem I (PSI) ratio in woody shoots. Analysis of parameters of variable chlorophyll fluorescence revealed high PSII activity in grapevine shoot cortex and demonstrated improved freeze tolerance and higher sensitivity to light of photosynthetic apparatus in grape vine in comparison to leaves. It was shown for the first time that photosynthetic apparatus in chlorenchyma cells of vine undergoes so-called “state-transition”–fast rearrangements leading to redistribution of energy between photosystems. Analysis of fatty acid (FA) compositions of lipids in examined tissues showed that the FA unsaturation index in green tissue of vine is lower than in leaves. A distinct feature of FA compositions of lipids in vine cortex was relatively high level of linoleic acid.     

Acclimation of Chlamydomonas reinhardtii to different growth irradiances

We report on the changes the photosynthetic apparatus of Chlamydomonas reinhardtii undergoes upon acclimation to different light intensity. When grown in high light, cells had a faster growth rate and higher biomass production compared with low and control light conditions. However, cells acclimated to low light intensity are indeed able to produce more biomass per photon available as compared with high light-acclimated cells, which dissipate as heat a large part of light absorbed, thus reducing their photosynthetic efficiency. This dissipative state is strictly dependent on the accumulation of LhcSR3, a protein related to light-harvesting complexes, responsible for nonphotochemical quenching in microalgae. Other changes induced in the composition of the photosynthetic apparatus upon high light acclimation consist of an increase of carotenoid content on a chlorophyll basis, particularly zeaxanthin, and a major down-regulation of light absorption capacity by decreasing the chlorophyll content per cell. Surprisingly, the antenna size of both photosystem I and II is not modulated by acclimation; rather, the regulation affects the PSI/PSII ratio. Major effects of the acclimation to low light consist of increased activity of state 1 and 2 transitions and increased contributions of cyclic electron flow.     

Functional Analysis of the Photosynthetic Apparatus of Prochlorothrix hollandica (Prochlorales), a Chlorophyll b Containing Procaryote

Light-shade adaptation of the chlorophyll a/b containing procaryote Prochlorothrix hollandica was studied in semicontinuous cultures adapted to 8, 80 and 200 μmole quanta per square meter per second. Chlorophyll a contents based on dry weight differed by a factor of 6 and chlorophyll b by a factor of 2.5 between the two extreme light conditions. Light utilization efficiencies determined from photosynthesis response curves were found to decrease in low light grown cultures due to lower light harvesting efficiencies; quantum requirements were constant at limiting and saturating irradiances for growth. At saturating growth irradiances, changes in light saturated oxygen evolution rate originated from changes in chlorophyll a antenna relative to the number of reaction centers II. At light-limiting conditions both the number of reaction centers II and the antenna size changed. The amount of chlorophyll b relative to reaction center II remained constant. As in cyanobacteria, the ratio of reaction center I to reaction center II was modulated during light-shade adaptation. On the other hand, time constants for photosynthetic electron transport (4 milliseconds) were low as observed in green algae and diatoms. The occurrence of state one to two and state two to one transitions is reported here. Another feature linking photosynthetic electron transport in P. hollandica to that in the eucaryotic photosynthetic apparatus was blockage of the state one to two transition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Although chlorophyll b was reported in association with photosystem I, the 630 nanometer light effect does not exclude that chlorophyll b is the photoreceptor for the state one to two transition.     

Specific Features of Plastid Pigment Apparatus and Photosynthesis in the Leaves of Ephemeroid and Summer Plants as Related to Photoinhibition

The state of the pigment apparatus and potential photosynthesis (PP) was compared in the leaves of plants falling into two ecological groups, ephemeroids (three species) and summer plants (two species). For the first time, the organization of the plastid pigment apparatus was investigated in ephemeroids using the data on chlorophyll and carotenoid distribution between the major photosynthetic pools. The molar ratio between xanthophylls and chlorophyll in the light-harvesting complex of plastids in the ephemeroids (0.5 to 0.6) considerably exceeded that in the summer plants (0.3–0.4). By using salicylaldoxime, an inhibitor of the reverse reaction of the violaxanthin cycle, we were able to calculate the active pool of violaxanthin on its way to zeaxanthin. This pool was shown to amount to 85% of the sum total of xanthophylls of the violaxanthin cycle in the ephemeroid leaf plastids as compared to 60% in the summer species. Thus, potentially, the photosynthetic apparatus in the ephemeroid leaves is better provided with the pigments essential for photoprotective function and for maintaining a high photosynthetic rate under early spring conditions. Under chilling temperatures of 5–10°C and full insolation, PP in ephemeroids was as high as in the summer plants at 20°C.     

Duree de vie et rendement de fluorescence de la chlorophylle in vivo. Leur relation dans differents modeles d'unites photosynthetiques

Lifetime and yield of chlorophyll fluorescence in vivo: Their relationship in different models of photosynthetic unitsWe have used phase fluorimetry to measure the relation between fluorescence lifetime (τ) and yield (Ф) of chlorophyll during the induction phase of photosynthesis in isolated chloroplasts and in vivo. This relationship is usually non-linear, curving slightly toward negative values of τ, and does not extrapolate to zero. In the discussion we examine the conditions which might give rise to curvature and a non-zero intercept. A model of connected photosynthetic units, characterized by an intersystem frequency of energy exchange, T, can account for the concavity of the experimental curves when 0.6 ? T ? 1 ns^?1.Two hypotheses are suggested to account for the non-zero intercept: the occurrence of sensitized fluorescence emission, or the existence in the initial fluorescence of a constant fraction independent of System II.     

Kontrolle der Eiablage der Brachfliege (Leptohylemyia coarctata Fallén) als Voraussetzung für die Befallsprognose und Bekämpfung

Study of bean plants infected by tabacco mosaic virus and potato X virus was performed. Virus infection of bean plants induced the injury of structural state of photosynthetic apparatus, viz., the a/b chlorophyll ratio decreased and the main photosynthetic membrane lipid monogalactosyl diacylglycerol degradation took place with parallel accumulation of intermediate compound suggested to perform a signal function. Phospholipid and free sterol content increase pointed out on the changes of the membrane fluidity and permeability. Accumulation of sulphoquinovosyl diacylglycerol in infected plants evidences the probability of latter to play important roles in adaptive reactions of photosynthetic apparatus.     

Variable chlorophyll fluorescence and its use for assessing physiological condition of plant photosynthetic apparatus

Analysis of plant behavior under diverse environmental conditions would be impossible without the methods for adequate assessment of the processes occurring in plants. The photosynthetic apparatus and its reaction to stress factors provide a reliable source of information on plant condition. One of the most informative methods based on monitoring the plant biophysical characteristics consists in detection and analysis of chlorophyll a fluorescence. Fluorescence is mainly emitted by chlorophyll a from the antenna complexes of photosystem II (PSII). However, fluorescence depends not only on the processes in the pigment matrix or PSII reaction centers but also on the redox reactions at the PSII donor and acceptor sides and even in the entire electron transport chain. Presently, a large variety of fluorometers from various manufacturers are available. Although application of such fluorometers does not require specialized training, the correct interpretation of the results would need sufficient knowledge for converting the instrumental data into the information on the condition of analyzed plants. This review is intended for a wide range of specialists employing fluorescence techniques for monitoring the physiological plant condition. It describes in a comprehensible way the theoretical basis of light emission by chlorophyll molecules, the origin of variable fluorescence, as well as relations between the fluorescence parameters, the redox state of electron carriers, and the light reactions of photosynthesis. Approaches to processing and analyzing the fluorescence induction curves are considered in detail on the basis of energy flux theory in the photosynthetic apparatus developed by Prof. Reto J. Strasser and known as a “JIP-test.” The physical meaning and relation of each calculated parameter to certain photosynthetic characteristics are presented, and examples of using these parameters for the assessment of plant physiological condition are outlined.     

Pigment ligation to proteins of the photosynthetic apparatus in higher plants

Ligation of pigments to proteins of the thylakoid membrane is a central step in the assembly of the photosynthetic apparatus in higher plants. Because of the potentially damaging photooxidative activity of chlorophylls, it is likely that between their biosynthesis and final assembly, chlorophylls will always be bound to protein complexes in which photooxidation is prevented by quenchers such as carotenoids. Such complexes may include chlorophyll carriers and/or membrane receptors involved in protein insertion into the membrane. Many if not all pigment-protein complexes of the thylakoid are stabilised towards protease attack by bound pigments. The major light-harvesting chlorophyll a/b protein (Lhebl,2) folds into its native structure in vitro only when it binds pigments. Pigment-induced folding may also be a general feature of chlorophyll-carotenoid proteins of the photosynthetic apparatus.     

Response of the photosynthetic apparatus of cotton (Gossypium hirsutum) to the onset of drought stress under field conditions studied by gas-exchange analysis and chlorophyll fluorescence imaging.

The functioning of the photosynthetic apparatus of cotton (Gossypium hirsutum) grown during the onset of water limitation was studied by gas-exchange and chlorophyll fluorescence to better understand the adaptation mechanisms of the photosynthetic apparatus to drought conditions. For this, cotton was grown in the field in Central Asia under well-irrigated and moderately drought-stressed conditions. The light and CO(2) responses of photosynthesis (A(G)), stomatal conductance (g(s)) and various chlorophyll fluorescence parameters were determined simultaneously. Furthermore, chlorophyll fluorescence images were taken from leaves to study the spatial pattern of photosystem II (PSII) efficiency and non-photochemical quenching parameters. Under low and moderate light intensity, the onset of drought stress caused an increase in the operating quantum efficiency of PSII photochemistry (varphi(PSII)) which indicated increased photorespiration since photosynthesis was hardly affected by water limitation. The increase in varphi(PSII) was caused by an increase of the efficiency of open PSII reaction centers (F(v)'/F(m)') and by a decrease of the basal non-photochemical quenching (varphi(NO)). Using a chlorophyll fluorescence imaging system a low spatial heterogeneity of varphi(PSII) was revealed under both irrigation treatments. The increased rate of photorespiration in plants during the onset of drought stress can be seen as an acclimation process to avoid an over-excitation of PSII under more severe drought conditions.