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# Photosynthesis Research - Current Research Articles

## Current research articles: Photosynthesis

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... is an international journal open to papers of merit dealing with both basic and applied aspects of photosynthesis.

# Current articles of the journal:

## A loop unique to ferredoxin-dependent glutamate synthases is not absolutely essential for ferredoxin-dependent catalytic activity

### Abstract

It had been proposed that a loop, typically containing 26 or 27 amino acids, which is only present in monomeric, ferredoxin-dependent, “plant-type” glutamate synthases and is absent from the catalytic ?-subunits of both NADPH-dependent, heterodimeric glutamate synthases found in non-photosynthetic bacteria and NADH-dependent heterodimeric cyanobacterial glutamate synthases, plays a key role in productive binding of ferredoxin to the plant-type enzymes. Site-directed mutagenesis has been used to delete the entire 27 amino acid-long loop in the ferredoxin-dependent glutamate synthase from the cyanobacterium Synechocystis sp. PCC 6803. The specific activity of the resulting loopless variant of this glutamate synthase, when reduced ferredoxin serves as the electron donor, is actually higher than that of the wild-type enzyme, suggesting that this loop is not absolutely essential for efficient electron transfer from reduced ferredoxin to the enzyme. These results are consistent with the results of an in-silico study that suggests that the loop is unlikely to interact directly with ferredoxin in the energetically most favorable model of a 1:1 complex of ferredoxin with the wild-type enzyme.

Posted on 1 February 2015 | 1:00 am

## Production of ketocarotenoids in tobacco alters the photosynthetic efficiency by reducing photosystem II supercomplex and LHCII trimer stability

### Abstract

The consequences of ketocarotenoid production in transgenic tobacco (Nicotiana tabacum) plants expressing a Chlamydomonas reinhardtii gene encoding a ?-carotene ketolase were examined concerning the functionality of the photosynthetic apparatus. T1 plants produced less photosynthetic pigments per dry weight, but Chl a/Chl b ratios remained unchanged. Almost as much ketocarotenoids as accessory xanthophylls accumulated per Chl a molecule. These ketocarotenoids were found mainly in the thylakoid membranes, but were not functionally bound to light-harvesting complexes, although LHCII is known to be able to bind astaxanthin. On the contrary, high amounts of ketocarotenoids probably changed the properties of the lipid phase of the thylakoids, thereby reducing the stability of photosystem II supercomplexes and LHCII trimers and ultimately decreasing grana formation. In addition, photosystem II function in electron transport was impaired, and plants exhibited less non-photochemical quenching compared to wild-type plants. Thus, in order not to disturb vital functions of the plants, production of astaxanthin and other nutritionally valuable ketocarotenoids apparently requires ways to sequester the additional carotenoids to plastoglobuli.

Posted on 1 February 2015 | 1:00 am

## A stable and efficient nuclear transformation system for the diatom Chaetoceros gracilis

### Abstract

Chaetoceros gracilis belongs to the centric diatoms, and has recently been used in basic research on photosynthesis. In addition, it has been commercially used in fisheries and is also attracting interest as a feedstock for biofuels production and biorefinery. In this study, we developed an efficient genetic transformation system for C. gracilis. The diatom cells were transformed via multi-pulse electroporation using plasmids containing various promoters to drive expression of the nourseothricin acetyltransferase gene (nat) as a selectable marker. The transformation efficiency reached ~400 positive transgenic clones per 108 recipient cells, which is the first example of successful transformation with electroporation in a centric diatom species. We further produced two expression vectors: the vector pCgLhcr5p contains the light-dependent promoter of a fucoxanthin chlorophyll a/c binding protein gene and the vector pCgNRp contains the inducible promoter of a nitrate reductase gene to drive the expression of introduced genes. In both vectors, an acetyl-CoA acetyltransferase promoter drives nat gene expression for antibiotic selection. Stable integration and expression of reporter genes, such as the firefly luciferase and green fluorescent protein Azami–Green genes, were observed in transformed C. gracilis cells. This efficient and stable transformation system for C. gracilis will enable both functional analysis of diatom-specific genes and strain improvement for further biotechnological applications.

Posted on 1 February 2015 | 1:00 am

## Photorespiration and nitrate assimilation: a major intersection between plant carbon and nitrogen

### Abstract

C3 carbon fixation has a bad reputation, primarily because it is associated with photorespiration, a biochemical pathway thought to waste a substantial amount of the carbohydrate produced in a plant. This review presents evidence collected over nearly a century that (1) Rubisco when associated with Mn2+ generates additional reductant during photorespiration, (2) this reductant participates in the assimilation of nitrate into protein, and (3) this nitrate assimilation facilitates the use of a nitrogen source that other organisms tend to avoid. This phenomenon explains the continued dominance of C3 plants during the past 23 million years of low CO2 atmospheres as well as the decline in plant protein concentrations as atmospheric CO2 rises.

Posted on 1 February 2015 | 1:00 am

## Temperature responses of the Rubisco maximum carboxylase activity across domains of life: phylogenetic signals, trade-offs, and importance for carbon gain

### Abstract

Temperature response of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalytic properties directly determines the CO2 assimilation capacity of photosynthetic organisms as well as their survival in environments with different thermal conditions. Despite unquestionable importance of Rubisco, the comprehensive analysis summarizing temperature responses of Rubisco traits across lineages of carbon-fixing organisms is lacking. Here, we present a review of the temperature responses of Rubisco carboxylase specific activity ( $$k_{\text{cat}}^{\text{c}}$$ ) within and across domains of life. In particular, we consider the variability of temperature responses, and their ecological, physiological, and evolutionary controls. We observed over two-fold differences in the energy of activation (?H a) among different groups of photosynthetic organisms, and found significant differences between C3 plants from cool habitats, C3 plants from warm habitats and C4 plants. According to phylogenetically independent contrast analysis, ?H a was not related to the species optimum growth temperature (T growth), but was positively correlated with Rubisco specificity factor (S c/o) across all organisms. However, when only land plants were analyzed, ?H a was positively correlated with both T growth and S c/o, indicating different trends for these traits in plants versus unicellular aquatic organisms, such as algae and bacteria. The optimum temperature (T opt) for $$k_{\text{cat}}^{\text{c}}$$ correlated with S c/o for land plants and for all organisms pooled, but the effect of T growth on T opt was driven by species phylogeny. The overall phylogenetic signal was significant for all analyzed parameters, stressing the importance of considering the evolutionary framework and accounting for shared ancestry when deciphering relationships between Rubisco kinetic parameters. We argue that these findings have important implications for improving global photosynthesis models.

Posted on 1 February 2015 | 1:00 am

## Gordon research conference on photosynthesis: from evolution of fundamental mechanisms to radical re-engineering

### Abstract

We provide here a News Report on the 2014 Gordon Research Conference on Photosynthesis, with the subtitle “From Evolution of Fundamental Mechanisms to Radical Re-Engineering.” It was held at Mount Snow Resort, West Dover, Vermont, during August 10–15, 2014. After the formal sessions ended, four young scientists (Ute Ambruster of USA; Han Bao of USA; Nicoletta Liguori of the Netherlands; and Anat Shperberg-Avni of Israel) were recognized for their research; they each received a book from one of us (G) in memory of Colin A. Wraight (1945–2014), a brilliant and admired scientist who had been very active in the bioenergetics field in general and in past Gordon Conferences in particular, having chaired the 1988 Gordon Conference on Photosynthesis. (See an article on Wraight by one of us (Govindjee) at http://www.life.illinois.edu/plantbio/Features/ColinWraight/ColinWraight.html.)

Posted on 1 February 2015 | 1:00 am

## Quantifying the effects of light intensity on bioproduction and maintenance energy during photosynthetic growth of Rhodobacter sphaeroides

### Abstract

Obtaining a better understanding of the physiology and bioenergetics of photosynthetic microbes is an important step toward optimizing these systems for light energy capture or production of valuable commodities. In this work, we analyzed the effect of light intensity on bioproduction, biomass formation, and maintenance energy during photoheterotrophic growth of Rhodobacter sphaeroides. Using data obtained from steady-state bioreactors operated at varying dilution rates and light intensities, we found that irradiance had a significant impact on biomass yield and composition, with significant changes in photopigment, phospholipid, and biopolymer storage contents. We also observed a linear relationship between incident light intensity and H2 production rate between 3 and 10 W m?2, with saturation observed at 100 W m?2. The light conversion efficiency to H2 was also higher at lower light intensities. Photosynthetic maintenance energy requirements were also significantly affected by light intensity, with links to differences in biomass composition and the need to maintain redox homeostasis. Inclusion of the measured condition-dependent biomass and maintenance energy parameters and the measured photon uptake rate into a genome-scale metabolic model for R. sphaeroides (iRsp1140) significantly improved its predictive performance. We discuss how our analyses provide new insights into the light-dependent changes in bioenergetic requirements and physiology during photosynthetic growth of R. sphaeroides and potentially other photosynthetic organisms.

Posted on 1 February 2015 | 1:00 am

## Andrew Benson honored on birthday ? 97

### Abstract

We present a brief account of the 97th birthday celebration of Andrew A. Benson, a scientific legend who is known, among other contributions, for his pioneering work on the path of carbon in photosynthesis (the Calvin-Benson cycle).

Posted on 1 February 2015 | 1:00 am

## Canopy light heterogeneity drives leaf anatomical, eco-physiological, and photosynthetic changes in olive trees grown in a high-density plantation

### Abstract

In the field, leaves may face very different light intensities within the tree canopy. Leaves usually respond with light-induced morphological and photosynthetic changes, in a phenomenon known as phenotypic plasticity. Canopy light distribution, leaf anatomy, gas exchange, chlorophyll fluorescence, and pigment composition were investigated in an olive (Olea europaea, cvs. Arbequina and Arbosana) orchard planted with a high-density system (1,250 trees ha?1). Sampling was made from three canopy zones: a lower canopy (<1 m), a central one (1–2 m), and an upper one (>2 m). Light interception decreased significantly in the lower canopy when compared to the central and top ones. Leaf angle increased and photosynthetic rates and non-photochemical quenching (NPQ) decreased significantly and progressively from the upper canopy to the central and the lower canopies. The largest leaf areas were found in the lower canopy, especially in the cultivar Arbequina. The palisade and spongy parenchyma were reduced in thickness in the lower canopy when compared to the upper one, in the former due to a decrease in the number of cell layers from three to two (clearly distinguishable in the light and fluorescence microscopy images). In both cultivars, the concentration of violaxanthin-cycle pigments and ?-carotene was higher in the upper than in the lower canopy. Furthermore, the de-epoxidized forms zeaxanthin and antheraxanthin increased significantly in those leaves from the upper canopy, in parallel to the NPQ increases. In conclusion, olive leaves react with morphological and photosynthetic changes to within-crown light gradients. These results strengthen the idea of olive trees as “modular organisms” that adjust the modules morphology and physiology in response to light intensity.

Posted on 1 February 2015 | 1:00 am

## Role of coherent vibrations in energy transfer and conversion in photosynthetic pigment–protein complexes

### Abstract

Oscillatory features of two-dimensional spectra of photosynthetic pigment–protein complexes during few picoseconds after electronic excitations of chlorophylls in various pigment–proteins were recently related to the coherent nuclear vibrations. It has been also speculated that the vibrations may assist the excitonic energy transfer and charge separation, hence contributing to energy transport and energy conversion efficiency. Here, we consider three theoretical approaches usually used for characterization of the excitation dynamics and charge separation, namely Redfield, Förster, and Marcus model descriptions, regarding this question. We show that two out of the three mechanisms require explicit resonances of excitonic splittings and the nuclear vibration frequencies. However, the third one related to the electron transfer is in principle off resonant.

Posted on 25 January 2015 | 1:00 am

## Electron transport kinetics in the diazotrophic cyanobacterium Trichodesmium spp. grown across a range of light levels

### Abstract

The diazotrophic cyanobacterium Trichodesmium is a major contributor to marine nitrogen fixation. We analyzed how light acclimation influences the photophysiological performance of Trichodesmium IMS101 during exponential growth in semi-continuous nitrogen fixing cultures under light levels of 70, 150, 250, and 400 ?mol photons m?2 s?1, across diel cycles. There were close correlations between growth rate, trichome length, particulate organic carbon and nitrogen assimilation, and cellular absorbance, which all peaked at 150 ?mol photons m?2 s?1. Growth rate was light saturated by about 100 ?mol photons m?2 s?1 and was photoinhibited above 150 ?mol photons m?2 s?1. In contrast, the light level (I k) to saturate PSII electron transport (e ?  PSII?1 s?1) was much higher, in the range of 450–550 ?mol photons m?2 s?1, and increased with growth light. Growth rate correlates with the absorption cross section as well as with absorbed photons per cell, but not to electron transport per PSII; this disparity suggests that numbers of PSII in a cell, along with the energy allocation between two photosystems and the state transition mechanism underlie the changes in growth rates. The rate of state transitions after a transfer to darkness increased with growth light, indicating faster respiratory input into the intersystem electron transport chain.

Posted on 24 January 2015 | 1:00 am

## Assessment of the impact of photosystem I chlorophyll fluorescence on the pulse-amplitude modulated quenching analysis in leaves of Arabidopsis thaliana

### Abstract

In their natural environment, plants are exposed to varying light conditions, which can lead to a build-up of excitation energy in photosystem (PS) II. Non-photochemical quenching (NPQ) is the primary defence mechanism employed to dissipate this excess energy. Recently, we developed a fluorescence-quenching analysis procedure that enables the protective effectiveness of NPQ in intact Arabidopsis leaves to be determined. However, pulse-amplitude modulation measurements do not currently allow distinguishing between PSII and PSI fluorescence levels. Failure to account for PSI contribution is suggested to lead to inaccurate measurements of NPQ and, particularly, maximum PSII yield (F v/F m). Recently, Pfündel et al. (Photosynth Res 114:189–206, 2013) proposed a method that takes into account PSI contribution in the measurements of F o fluorescence level. However, when PSI contribution was assumed to be constant throughout the induction of NPQ, we observed lower values of the measured minimum fluorescence level ( $${F_{{\text{o}}_{\text{calc.}}^{^\prime }}}$$ ) than those calculated according to the formula of Oxborough and Baker (Photosynth Res 54:135–142 1997) ( $${F_{{\text{o}}_{\text{calc.}}^{^\prime } }}$$ ), regardless of the light intensity. Therefore, in this work, we propose a refined model to correct for the presence of PSI fluorescence, which takes into account the previously observed NPQ in PSI. This method efficiently resolves the discrepancies between measured and calculated F o? produced by assuming a constant PSI fluorescence contribution, whilst allowing for the correction of the maximum PSII yield.

Posted on 23 January 2015 | 1:00 am

## Excitation migration in fluctuating light-harvesting antenna systems

### Abstract

Complex multi-exponential fluorescence decay kinetics observed in various photosynthetic systems like photosystem II (PSII) have often been explained by the reversible quenching mechanism of the charge separation taking place in the reaction center (RC) of PSII. However, this description does not account for the intrinsic dynamic disorder of the light-harvesting proteins as well as their fluctuating dislocations within the antenna, which also facilitate the repair of RCs, state transitions, and the process of non-photochemical quenching. Since dynamic fluctuations result in varying connectivity between pigment–protein complexes, they can also lead to non-exponential excitation decay kinetics. Based on this presumption, we have recently proposed a simple conceptual model describing excitation diffusion in a continuous medium and accounting for possible variations of the excitation transfer pathways. In the current work, this model is further developed and then applied to describe fluorescence kinetics originating from very diverse antenna systems, ranging from PSII of various sizes to LHCII aggregates and even the entire thylakoid membrane. In all cases, complex multi-exponential fluorescence kinetics are perfectly reproduced on the entire relevant time scale without assuming any radical pair equilibration at the side of the excitation quencher, but using just a few parameters reflecting the mean excitation energy transfer rate as well as the overall average organization of the photosynthetic antenna.

Posted on 22 January 2015 | 1:00 am

## Energy transfer in Anabaena variabilis filaments under nitrogen depletion, studied by time-resolved fluorescence

### Abstract

Some filamentous cyanobacteria (including Anabaena) differentiate into heterocysts under nitrogen-depleted conditions. During differentiation, the phycobiliproteins and photosystem II in the heterocysts are gradually degraded. Nitrogen depletion induces changes in the pigment composition of both vegetative cells and heterocysts, which affect the excitation energy transfer processes. To investigate the changes in excitation energy transfer processes of Anabaena variabilis filaments grown in standard medium (BG11) and a nitrogen-free medium (BG110), we measured their steady-state absorption spectra, steady-state fluorescence spectra, and time-resolved fluorescence spectra (TRFS) at 77 K. TRFS were measured with a picosecond time-correlated single photon counting system. The pigment compositions of the filaments grown in BG110 changed throughout the growth period; the relative phycocyanin levels monotonically decreased, whereas the relative carotenoid (Car) levels decreased and then recovered to their initial value (at day 0), with formation of lower-energy Cars. Nitrogen starvation also altered the fluorescence kinetics of PSI; the fluorescence maximum of TRFS immediately after excitation occurred at 735, 740, and 730 nm after 4, 8, and 15 days growth in BG110, respectively. Based on these results, we discuss the excitation energy transfer dynamics of A. variabilis filaments under the nitrogen-depleted condition throughout the growth period.

Posted on 18 January 2015 | 1:00 am

## Establishment of the forward genetic analysis of the chlorophyll d -dominated cyanobacterium Acaryochloris marina MBIC 11017 by applying in vivo transposon mutagenesis system

### Abstract

Acaryochloris marina MBIC 11017 possesses chlorophyll (Chl) d as a major Chl, which enables this organism to utilize far-red light for photosynthesis. Thus, the adaptation mechanism of far-red light utilization, including Chl d biosynthesis, has received much attention, though a limited number of reports on this subject have been published. To identify genes responsible for Chl d biosynthesis and adaptation to far-red light, molecular genetic analysis of A. marina was required. We developed a transformation system for A. marina and introduced expression vectors into A. marina. In this study, the high-frequency in vivo transposon mutagenesis system recently established by us was applied to A. marina. As a result, we obtained mutants with the transposon in their genomic DNA at various positions. By screening transposon-tagged mutants, we isolated a mutant (Y1 mutant) that formed a yellow colony on agar medium. In the Y1 mutant, the transposon was inserted into the gene encoding molybdenum cofactor biosynthesis protein A (MoaA). The Y1 mutant was functionally complemented by introducing the moaA gene or increasing the ammonium ion in the medium. These results indicate that the mutation of the moaA gene reduced nitrate reductase activity, which requires molybdenum cofactor, in the Y1 mutant. This is the first successful forward genetic analysis of A. marina, which will lead to the identification of genes responsible for adaptation to far-red light.

Posted on 18 January 2015 | 1:00 am

## Small subunit of a cold-resistant plant, timothy, does not significantly alter the catalytic properties of Rubisco in transgenic rice

### Abstract

Effects of overexpression of high activity-type Rubisco small subunit (RbcS) from a cold-resistant plant, timothy (Phleum pratense), on kinetic properties of Rubisco were studied in rice (Oryza sativa). The full-length mRNA sequence of timothy RbcS (PpRbcS1) was determined by 5?RACE and 3?RACE. The coding sequence of PpRbcS1 was fused to the chlorophyll a/b-binding protein promoter and introduced into rice. PpRbcS was highly expressed in leaf blade and accounted for approximately 30 % of total RbcS in homozygous transgenic lines. However, the catalytic turnover rate and K m for CO2 of Rubisco did not significantly change in these transgenic lines compared to non-transgenic rice, suggesting that PpRbcS1 is not effective for improvement of catalytic efficiency of rice Rubisco. The photosynthetic rate and growth were essentially unchanged, whereas the photosynthetic rate at low CO2 condition was marginally increased in transgenic lines. Rubisco content was significantly increased, whereas soluble protein, nitrogen, and chlorophyll contents were unchanged in transgenic lines compared to non-transgenic rice. Because the kinetic properties were similar, observed slight increase in photosynthetic rate at low CO2 is considered to be large due to increase in Rubisco content in transgenic lines. Introduction of foreign RbcS is an effective approach for the improvement of Rubisco kinetics and photosynthesis. However, in this study, it was suggested that RbcS of high activity-type Rubisco, even showing higher amino acid identity with rice RbcS, did not always enhance the catalytic turnover rate of Rubisco in rice. Thus, we should carefully select RbcS to be overexpressed before introduction.

Posted on 17 January 2015 | 1:00 am

## Genetic and genomic analysis of RNases in model cyanobacteria

### Abstract

Cyanobacteria are diverse photosynthetic microbes with the ability to convert CO2 into useful products. However, metabolic engineering of cyanobacteria remains challenging because of the limited resources for modifying the expression of endogenous and exogenous biochemical pathways. Fine-tuned control of protein production will be critical to optimize the biological conversion of CO2 into desirable molecules. Messenger RNAs (mRNAs) are labile intermediates that play critical roles in determining the translation rate and steady-state protein concentrations in the cell. The majority of studies on mRNA turnover have focused on the model heterotrophic bacteria Escherichia coli and Bacillus subtilis. These studies have elucidated many RNA modifying and processing enzymes and have highlighted the differences between these Gram-negative and Gram-positive bacteria, respectively. In contrast, much less is known about mRNA turnover in cyanobacteria. We generated a compendium of the major ribonucleases (RNases) and provide an in-depth analysis of RNase III-like enzymes in commonly studied and diverse cyanobacteria. Furthermore, using targeted gene deletion, we genetically dissected the RNases in Synechococcus sp. PCC 7002, one of the fastest growing and industrially attractive cyanobacterial strains. We found that all three cyanobacterial homologs of RNase III and a member of the RNase II/R family are not essential under standard laboratory conditions, while homologs of RNase E/G, RNase J1/J2, PNPase, and a different member of the RNase II/R family appear to be essential for growth. This work will enhance our understanding of native control of gene expression and will facilitate the development of an RNA-based toolkit for metabolic engineering in cyanobacteria.

Posted on 17 January 2015 | 1:00 am

## The Photosystem II D1-K238E mutation enhances electrical current production using cyanobacterial thylakoid membranes in a bio-photoelectrochemical cell

### Abstract

The conversion of solar energy (SEC) to storable chemical energy by photosynthesis has been performed by photosynthetic organisms, including oxygenic cyanobacteria for over 3 billion years. We have previously shown that crude thylakoid membranes from the cyanobacterium Synechocytis sp. PCC 6803 can reduce the electron transfer (ET) protein cytochrome c even in the presence of the PSII inhibitor DCMU. Mutation of lysine 238 of the Photosystem II D1 protein to glutamic acid increased the cytochrome reduction rates, indicating the possible position of this unknown ET pathway. In this contribution, we show that D1-K238E is rather unique, as other mutations to K238, or to other residues in the same vicinity, are not as successful in cytochrome c reduction. This observation indicates the sensitivity of ET reactions to minor changes. As the next step in obtaining useful SEC from biological material, we describe the use of crude Synechocystis membranes in a bio-photovoltaic cell containing an N-acetyl cysteine-modified gold electrode. We show the production of significant current for prolonged time durations, in the presence of DCMU. Surprisingly, the presence of cytochrome c was not found to be necessary for ET to the bio-voltaic cell.

Posted on 15 January 2015 | 1:00 am

## Differences in energy transfer of a cyanobacterium, Synechococcus sp. PCC 7002, grown in different cultivation media

### Abstract

Currently, cyanobacteria are regarded as potential biofuel sources. Large-scale cultivation of cyanobacteria in seawater is of particular interest because seawater is a low-cost medium. In the present study, we examined differences in light-harvesting and energy transfer processes in the cyanobacterium Synechococcus sp. PCC 7002 grown in different cultivation media, namely modified A medium (the optimal growth medium for Synechococcus sp. PCC 7002) and f/2 (a seawater medium). The concentrations of nitrate and phosphate ions were varied in both media. Higher nitrate ion and/or phosphate ion concentrations yielded high relative content of phycobilisome. The cultivation medium influenced the energy transfers within phycobilisome, from phycobilisome to photosystems, within photosystem II, and from photosystem II to photosystem I. We suggest that the medium also affects charge recombination at the photosystem II reaction center and formation of a chlorophyll-containing complex.

Posted on 11 January 2015 | 1:00 am

## Light adaptation of the unicellular red alga, Cyanidioschyzon merolae , probed by time-resolved fluorescence spectroscopy

### Abstract

Photosynthetic organisms change the quantity and/or quality of their pigment–protein complexes and the interactions among these complexes in response to light conditions. In the present study, we analyzed light adaptation of the unicellular red alga Cyanidioschyzon merolae, whose pigment composition is similar to that of cyanobacteria because its phycobilisomes (PBS) lack phycoerythrin. C. merolae were grown under different light qualities, and their responses were measured by steady-state absorption, steady-state fluorescence, and picosecond time-resolved fluorescence spectroscopies. Cells were cultivated under four monochromatic light-emitting diodes (blue, green, yellow, and red), and changes in pigment composition and energy transfer were observed. Cells grown under blue and green light increased their relative phycocyanin levels compared with cells cultured under white light. Energy-transfer processes to photosystem I (PSI) were sensitive to yellow and red light. The contribution of direct energy transfer from PBS to PSI increased only under yellow light, while red light induced a reduction in energy transfer from photosystem II to PSI and an increase in energy transfer from light-harvesting chlorophyll protein complex I to PSI. Differences in pigment composition, growth, and energy transfer under different light qualities are discussed.

Posted on 11 January 2015 | 1:00 am