Effects of shading on photosynthetic characteristics and chlorophyll fluorescence parameters in leaves of Hydrangea macrophylla

Aims The objectives were to investigate the effects of different light intensities on photosynthetic characteristics and chlorophyll fluorescence parameters, to clarify the physiological responses and photo-protective mechanisms of Hydrangea macrophylla to changes in light regimes in view of the distribution of energy absorbed and photosynthetic characteristics.Methods Three light regimes including natural and shade (shading rate 50% and 75% of natural light) were applied to plants for 60 days. After the treatment, the gas-exchange, chlorophyll a fluorescence and photosynthesis-light curves were measured by a portable leaf gas exchange system (LI-6400).Important findings The results showed that the weak light intensity treatment reduced dark respiration rate, light compensation point and light saturation point of plant, but increased apparent quantum yield, suggesting that plants had the physiological strategy to utilize the weakening light by reducing respiration. The net photosynthetic rate, intercellular CO₂ concentration, transpiration rate and water use efficiency of plants grown below 50% of natural light showed significant difference compared with natural and shading rate 75% of natural light. There were significant difference between natural and shade treatments in the maximal quantum efficiency of PSII (F_v/F_m), as indicated that it was significantly less at full light than that at 50% of natural light. Initial fluorescence intensity (F_o) of plants was higher at full light than that at 50% of natural light, suggesting that photoinhibition occurred in natural light. The non-photochemical quenching (NQP) decreased with the aggravation of shade stress, indicating that shading decreased the efficiency of photochemical reaction by reducing the fraction of incident light in photochemical energy utilization and decreased thermal dissipation through regulating energy distribution in photosystem II (PSII) in the leaves of Hydrangea macrophylla. In general, the 70% of incident light in photochemical energy utilization was distributed to thermal dissipation, 20% was distributed to non-regulated energy dissipation and 4% was distributed to effective photochemical reaction. In conclusion, responses of plants to increased irradiance are governed by strategy: to utilize a high fraction of incident light in photochemistry and regulate energy dissipation in PSII and weaken the accumulation of excess excitation energy in PSII to protect the photosynthetic apparatus in the leaves of H. macrophylla under saturated radiation.     

连作土壤中施加球毛壳ND35菌肥对杨树生理特性的影响

在山东农业大学林学实验站杨树连作土壤中施加不同剂量(0.17、0.33、0.67、1.00、1.33和1.67 g·kg^-1)的球毛壳ND35菌肥,测定不同处理下一年生杨树叶片的光响应过程、叶绿素荧光以及叶黄素循环等光合生理生化指标,研究球毛壳ND35菌肥对杨树根系和光合生理性能的影响.结果表明: 随连作土壤中菌肥含量的增加,杨树叶片的叶绿素含量(Chl)呈增加趋势,电子传递速率(ETR)、净光合速率(P_n)、量子效率(Φ)、硝酸还原酶(NR)活性以及根系活力等生理指标均呈先增加后降低的趋势,依赖于叶黄素循环的光合热耗散呈降低趋势,而非光化学淬灭(NPQ)呈先降低后增加的趋势.在土壤施加菌肥剂量0.67和1.00 g·kg^-1处理时,光合机构的过剩光能减少,向光化学反应方向分配的光能增多,光能利用效率提高.在连作土壤中施加适量(0.67～1.00 g·kg^-1)的球毛壳ND35菌肥,能在一定程度上提高杨树的根系生理活性,提高杨树叶片对光能的利用效率,有利于改善杨树叶片的光合机构运转状态,提高叶片的光合作用效率.     

Differences in the physiological state between triticale and maize plants during drought stress and followed rehydration expressed by the leaf gas exchange and spectrofluorimetric methods

The studies were carried out in order to estimate differences in the physiological state between triticale and maize plants subjected to drought stress followed by rehydration. The physiological state of the plants was evaluated by measurements of leaf water potential, net photosynthesis, transpiration and stomatal conductance. Spectrofluorimetric methods for the study of blue, green and red fluorescence were applied. We observed that the soil drought induced a greater water loss in triticale leaves than in maize and consequently caused greater injuries to the photosynthetic apparatus. Moreover, triticale plant recovery was slower than in maize plants during the rehydration phase. The effect was probably connected with the higher functional and structural disorganisation of the photosynthetic apparatus observed during drought stress in triticale. Water stress is responsible for damages to photosystem PS II. The worst light utilisation in photosynthetic light conversion was recorded as an increase in the intensity of red fluorescence. Drought stress induced a strong increase in the intensity of blue and green fluorescence in the studied species and it was still high in maize plants during the first day of rehydration. Increase in the intensity of blue and green fluorescence in maize seems to be the effect of the photoprotection mechanism which prevents damage to PS II through utilisation of excess energy.     

热带雨林剑叶凤尾蕨(Pteris ensiformis)对光强变化的适应

野外调查表明剑叶凤尾蕨能适应不同的光环境,本研究测定剑叶凤尾蕨在两种不同光环境下的适应能力,在热带雨林林下和林窗生长40d后,林下生长的剑叶凤尾蕨比林窗生长的植株有较多的叶片数,大的冠幅,高的叶绿素含量和表观量子效率。同时。林下生长的剑叶凤尾蕨有高的光化学效率和较低的非光化学耗散能力,这说明低光植物表现出有较高的能量转换能力,而两种光强生长的剑叶凤尾蕨最大光合放氧速率相似。这可能与在高光下的非辐射耗散的提高和光合机构的损伤有关,研究结果表明,剑叶凤尾蕨通过光合器官的调整对不同光强的适应。以促进剑叶凤尾蕨在不同光环境的生长能力。     

热带雨林剑叶凤尾蕨(Pteris ensiformis)对光强变化的适应

野外调查表明剑叶凤尾蕨能适应不同的光环境.本研究测定剑叶凤尾蕨在两种不同光环境下的适应能力.在热带雨林林下和林窗生长40d后,林下生长的剑叶凤尾蕨比林窗生长的植株有较多的叶片数,大的冠幅,高的叶绿素含量和表观量子效率.同时,林下生长的剑叶凤尾蕨有高的光化学效率和较低的非光化学耗散能力,这说明低光植物表现出有较高的能量转换能力.而两种光强生长的剑叶凤尾蕨最大光合放氧速率相似,这可能与在高光下的非辐射耗散的提高和光合机构的损伤有关.研究结果表明,剑叶凤尾蕨通过光合器官的调整对不同光强的适应,以促进剑叶凤尾蕨在不同光环境的生长能力.     

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.     

On the evolution of the photosynthetic pigments

During the course of terrestrial evolution, some organisms developed the capability of capturing and utilizing solar radiation. Colored compounds were undoubtedly incorporated within living forms from the earliest times, but during the transition from heterotrophic to a photoautotrophic metabolism only those pigments were selected that were components of the evolving photosynthetic apparatus and were able to catalyze reactions involving storage of light energy in chemical bonds. In this communication, some properties of tetrapyrroles with a closed porphyrin ring containing a metal ion in the center are discussed. These compounds are present in all principal contemporary photosynthetic pigments, and their synthesis has been demonstrated from simpler compounds under prebiotic conditions. It is probable that during intermediate stages in the evolution of photosynthesis, pigments with oxidizing potentials lower than that of chlorophyll were utilized to store light energy although they were not capable of removing electrons from water. The evolution and function of multiple forms of a given photosynthetic pigmentin vivo are discussed. ‘Accessory’ pigments may be regarded as rudiments of the evolutionary development of the photosynthetic apparatus.     

A polyamine- and LHCII protease activity-based mechanism regulates the plasticity and adaptation status of the photosynthetic apparatus

In the present study we aim to dissect the basis of the polyamine mode of action in the structure and function of the photosynthetic apparatus. Although the modulating effects of polyamines in photosynthesis have been reported since long [K. Kotzabasis, A role for chloroplast-associated polyamines? Bot. Acta 109 (1996) 5-7], the underlying mechanisms remained until today largely unknown. The diamine putrescine was employed in this study, by being externally added to Scenedesmus obliquus cultures acclimated to either low or high light conditions. The results revealed the high efficiency by which putrescine can alter the levels of the major photosynthetic complexes in a concerted manner inducing an overall structure and function of the photosynthetic apparatus similar to that under higher light conditions. The revealed mechanism for this phenomenon involves alterations in the level of the polyamines putrescine and spermine which are bound to the photosynthetic complexes, mainly to the LHCII oligomeric and monomeric forms. In vitro studies point out to a direct impact of the polyamines on the autoproteolytic degradation of LHCII. Concomitantly to the reduction of the LHCII size, exogenously supplied putrescine, induces the reaction centers' density and thus the photosynthetic apparatus is adjusted as if it was adapted to higher light conditions. Thus polyamines, through LHCII, play a crucial role in the regulation of the photosynthetic apparatus' photoadaptation. The protective role of polyamines on the photosynthetic apparatus under various environmental stresses is also discussed in correlation to this phenomenon.     

On the evolution of the photosynthetic pigments.

During the course of terrestrial evolution, some organisms developed the capability of capturing and utilizing solar radiation. Colored compounds were undoubtedly incorporated within living forms from the earliest times, but during the transition from heterotrophic to a photoautotrophic metabolism only those pigments were selected that were components of the evolving photosynthetic apparatus and were able to catalyze reactions involving storage of light energy in chemical bonds. In this communication, some properties of tetrapyrroles with a closed porphyrin ring containing a metal ion in the center are discussed. These compounds are present in all principal contemporary photosynthetic pigments, and their synthesis has been demonstrated from simpler compounds under prebiotic conditions. It is probable that during intermediate stages in the evolution of photosynthesis, pigments with oxidizing potentials lower than that of chlorophyll were utilized to store light energy although they were not capable of removing electrons from water. The evolution and function of multiple forms of a given photosynthetic pigment in vivo are discussed. 'Accessory' pigments may be regarded as rudiments of the evolutionary development of the photosynthetic apparatus.     

A polyamine- and LHCII protease activity-based mechanism regulates the plasticity and adaptation status of the photosynthetic apparatus

In the present study we aim to dissect the basis of the polyamine mode of action in the structure and function of the photosynthetic apparatus. Although the modulating effects of polyamines in photosynthesis have been reported since long [K. Kotzabasis, A role for chloroplast-associated polyamines? Bot. Acta 109 (1996) 5-7], the underlying mechanisms remained until today largely unknown. The diamine putrescine was employed in this study, by being externally added to Scenedesmus obliquus cultures acclimated to either low or high light conditions. The results revealed the high efficiency by which putrescine can alter the levels of the major photosynthetic complexes in a concerted manner inducing an overall structure and function of the photosynthetic apparatus similar to that under higher light conditions. The revealed mechanism for this phenomenon involves alterations in the level of the polyamines putrescine and spermine which are bound to the photosynthetic complexes, mainly to the LHCII oligomeric and monomeric forms. In vitro studies point out to a direct impact of the polyamines on the autoproteolytic degradation of LHCII. Concomitantly to the reduction of the LHCII size, exogenously supplied putrescine, induces the reaction centers' density and thus the photosynthetic apparatus is adjusted as if it was adapted to higher light conditions. Thus polyamines, through LHCII, play a crucial role in the regulation of the photosynthetic apparatus' photoadaptation. The protective role of polyamines on the photosynthetic apparatus under various environmental stresses is also discussed in correlation to this phenomenon.     

Identification of genes required for recycling reducing power during photosynthetic growth

Photosynthetic organisms have the unique ability to transform light energy into reducing power. We study the requirements for photosynthesis in the alpha-proteobacterium Rhodobacter sphaeroides. Global gene expression analysis found that approximately 50 uncharacterized genes were regulated by changes in light intensity and O\2 tension, similar to the expression of genes known to be required for photosynthetic growth of this bacterium. These uncharacterized genes included RSP4157 to -4159, which appeared to be cotranscribed and map to plasmid P004. A mutant containing a polar insertion in RSP4157, CT01, was able to grow via photosynthesis under autotrophic conditions using H2 as an electron donor and CO2 as a carbon source. However, CT01 was unable to grow photoheterotrophically in a succinate-based medium unless compounds that could be used to recycle reducing power (the external electron acceptor dimethyl sulfoxide (DMSO) or CO2 were provided. This suggests that the insertion in RSP4157 caused a defect in recycling reducing power during photosynthetic growth when a fixed carbon source was present. CT01 had decreased levels of RNA for genes encoding putative glycolate degradation functions. We found that exogenous glycolate also rescued photoheterotrophic growth of CT01, leading us to propose that CO2 produced from glycolate metabolism can be used by the Calvin cycle to recycle reducing power generated in the photosynthetic apparatus. The ability of glycolate, CO2, or DMSO to support photoheterotrophic growth of CT01 suggests that one or more products of RSP4157 to -4159 serve a previously unknown role in recycling reducing power under photosynthetic conditions.     

Modifications to the photosynthetic apparatus of higher plants in response to changes in the light environment

A brief review of the photosynthetic apparatus of higher plants is given, followed by a consideration of the modifications induced in this apparatus by changes in light intensity and light quality. Possible strategies by which plants may optimize photosynthetic activity by both long- and short-term modifications of their photosynthetic apparatus in response to changing light regimes are discussed.     

Minimal genomes,maximal productivity: comparative genomics of the photosystem and light-harvesting complexes in the marine cyanobacterium, <Emphasis Type="Italic">Prochlorococcus</Emphasis>

Although Prochlorococcus isolates possess the smallest genomes of any extant photosynthetic organism, this genus numerically dominates vast regions of the world’s subtropical and tropical open oceans and has evolved to become an important contributor to global biogeochemical cycles. The sequencing of 12 Prochlorococcus genomes provides a glimpse of the extensive genetic heterogeneity and, thus, physiological potential of the lineage. In this study, we present an up-to-date comparative analysis of major proteins of the photosynthetic apparatus in 12 Prochlorococcus genomes. Our analyses reveal a striking diversity within the Prochlorococcus lineage in the major protein complexes of the photosynthetic apparatus. The heterogeneity that has evolved in the photosynthetic apparatus suggests versatility in strategies for optimizing photosynthesis under conditions of environmental variability and stress. This diversity could be particularly important in ensuring the survival of a lineage whose individuals have evolved minimal genomes and, thus, relatively limited repertoires for responding to environmental challenges. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Short-term acclimation of the photosynthetic electron transfer chain to changing light: a mathematical model

Photosynthetic eukaryotes house two photosystems with distinct light absorption spectra. Natural fluctuations in light quality and quantity can lead to unbalanced or excess excitation, compromising photosynthetic efficiency and causing photodamage. Consequently, these organisms have acquired several distinct adaptive mechanisms, collectively referred to as non-photochemical quenching (NPQ) of chlorophyll fluorescence, which modulates the organization and function of the photosynthetic apparatus. The ability to monitor NPQ processes fluorometrically has led to substantial progress in elucidating the underlying molecular mechanisms. However, the relative contribution of distinct NPQ mechanisms to variable light conditions in different photosynthetic eukaryotes remains unclear. Here, we present a mathematical model of the dynamic regulation of eukaryotic photosynthesis using ordinary differential equations. We demonstrate that, for Chlamydomonas, our model recapitulates the basic fluorescence features of short-term light acclimation known as state transitions and discuss how the model can be iteratively refined by comparison with physiological experiments to further our understanding of light acclimation in different species.     

A Method for the Study of the Kinetics of Photosynthesis at Constant Rate of Transpiration: RESULTS OBTAINED WITH RICE PLANTS (ORIZA SATIVA MARATELLI)

An apparatus has been built to study the kinetics of ionic andgaseous exchanges in intact living plants under strictly controlledconditions. The article describes only the equipment monitoringthe upper parts of plants, where light intensity, air-flow rate,temperature, humidity, CO₂ concentration, and the rates of transpirationand apparent photosynthesis are independently controlled. Theperformance of the apparatus is illustrated by elementary butvery reliable results on apparent photosynthesis in rice plants.A dual mechanism has been revealed by the experiments. Combinedeffects of light intensity and of CO₂ concentration, both intheir lower ranges, confirm the well-known quantized actionof light energy in the basic photosynthetic process.     

Proteomic characterization of the Rhodobacter sphaeroides 2.4.1 photosynthetic membrane: identification of new proteins

The Rhodobacter sphaeroides intracytoplasmic membrane (ICM) is an inducible membrane that is dedicated to the major events of bacterial photosynthesis, including harvesting light energy, separating primary charges, and transporting electrons. In this study, multichromatographic methods coupled with Fourier transform ion cyclotron resonance mass spectrometry, combined with subcellular fractionation, was used to test the hypothesis that the photosynthetic membrane of R. sphaeroides 2.4.1 contains a significant number of heretofore unidentified proteins in addition to the integral membrane pigment-protein complexes, including light-harvesting complexes 1 and 2, the photochemical reaction center, and the cytochrome bc(1) complex described previously. Purified ICM vesicles are shown to be enriched in several abundant, newly identified membrane proteins, including a protein of unknown function (AffyChip designation RSP1760) and a possible alkane hydroxylase (RSP1467). When the genes encoding these proteins are mutated, specific photosynthetic phenotypes are noted, illustrating the potential new insights into solar energy utilization to be gained by this proteomic blueprint of the ICM. In addition, proteins necessary for other cellular functions, such as ATP synthesis, respiration, solute transport, protein translocation, and other physiological processes, were also identified to be in association with the ICM. This study is the first to provide a more global view of the protein composition of a photosynthetic membrane from any source. This protein blueprint also provides insights into potential mechanisms for the assembly of the pigment-protein complexes of the photosynthetic apparatus, the formation of the lipid bilayer that houses these integral membrane proteins, and the possible functional interactions of ICM proteins with activities that reside in domains outside this specialized bioenergetic membrane.     

Structural and functional heterogeneity in the major light-harvesting complexes of higher plants

The major light-harvesting complex (LHC IIb) of higher plants plays a crucial role in capturing light energy for photosynthesis and in regulating the flow of energy within the photosynthetic apparatus. Multiple isoforms of the protein bind chlorophyll and xanthophyll chromophores, but it is commonly believed that the pigment-binding properties of different LHC IIb complexes are conserved within and between species. We have investigated the structure and function of different LHC IIb complexes isolated from Arabidopsis thaliana grown under different light conditions. LHC IIb isolated from low light-grown plants shows increased amounts of the Lhcb2 gene product, increased binding of chlorophyll a, and altered energy transfer characteristics. We suggest that Lhcb2 specifically binds at least one additional chlorophyll a compared to the Lhcb1 gene product, and that differences in the functioning of LHC IIb from high and low light-grown plants are a direct consequence of the change in polypeptide composition. We show that changes in LHC IIb composition are accompanied by changes in photosynthetic function in vivo and discuss the possible functional significance of LHC IIb heterogeneity.     

Physiological responses and photo-protective mechanisms of two Rhododendron plants to natural sunlight after long term shading

AimsResponses of plants to increased irradiance are governed by two strategies: an increase in the utilization of absorbed light and photo-protective mechanisms. Varied physiological responses to increased irradiance were observed in plant species with differing adaptabilities to light regimes. This research aims to explore the physiological responses and photo-protective mechanisms of two Rhododendron plants to changes in light regimes. MethodsChlorophyll fluorescence parameters and rapid light curves were measured for leaves of R. hybrida (a shade-tolerant species) and R. simsii (a light-loving and shade-tolerant species) following exposure to sunlight for five days after growing in the shade for one year.Important findings Natural sunlight decreased the efficiency of photochemical reaction by reducing the fraction of incident light in photochemical energy utilization and decreased thermal dissipation through regulating energy dissipation in photosystem II (PSII) in the leaves of R. hybrida. As a result, natural sunlight induced the accumulation of excess excitation energy in PSII, and caused photo-inhibition and even photodamage in the leaves of R. hybrida, which was suddenly transferred from long-term shading to sun exposures. The acclimation capacity to changes of growth light regimes was stronger in R. simsii than in R. hybrida, due to a higher capability for photochemical reaction, thermal dissipation and cyclic electron flows around photosystem I in the leaves of R. simsii. Rhododendron simsii could utilize a high fraction of incident light in photochemistry and regulate energy dissipation in PSII to protect the photosynthetic apparatus under both shading and natural sunlight condition. Therefore, high light intensity under natural sunlight did not cause photo-inhibition in R. simsii.