The process of photosynthesis is initiated by the capture of sunlight by a network of light-absorbing molecules (chromophores), which are also responsible for the subsequent funneling of the excitation energy to the reaction centers. Through evolution, genetic drift, and speciation, photosynthetic organisms have discovered many solutions for light harvesting. In this review, we describe the underlying photophysical principles by which this energy is absorbed, as well as the mechanisms of electronic excitation energy transfer (EET). First, optical properties of the individual pigment chromophores present in light-harvesting antenna complexes are introduced, and then we examine the collective behavior of pigment−pigment and pigment−protein interactions. The description of energy transfer, in particular multichromophoric antenna structures, is shown to vary depending on the spatial and energetic landscape, which dictates the relative coupling strength between constituent pigment molecules. In the latter half...

Light Absorption and Energy Transfer in the Antenna Complexes of Photosynthetic Organisms.

C-phycocyanin (C-PC) is a blue pigment in cyanobacteria, rhodophytes and cryptophytes with fluorescent and antioxidative properties. C-PC is presently extracted from open pond cultures of the cyanobacterium Arthrospira platensis although these cultures are not very productive and open for contaminating organisms. C-PC is considered a healthy ingredient in cyanobacterial-based foods and health foods while its colouring, fluorescent or antioxidant properties are utilised only to a minor extent. However, recent research and developments in C-PC synthesis and functionality have expanded the potential applications of C-PC in biotechnology, diagnostics, foods and medicine: The productivity of C-PC has been increased in heterotrophic, high cell density cultures of the rhodophyte Galdieria sulphuraria that are grown under well-controlled and axenic conditions. C-PC purification protocols based on various chromatographic principles or novel two-phase aqueous extraction methods have expanded in numbers and improved in performance. The functionality of C-PC as a fluorescent dye has been improved by chemical stabilisation of C-PC complexes, while protein engineering has also introduced increased stability and novel biospecific binding sites into C-PC fusion proteins. Finally, our understanding of the physiological functions of C-PC in humans has been improved by a mechanistic hypothesis that links the chemical properties of the phycocyanobilin chromophores of C-PC to the natural antioxidant, bilirubin, and may explain the observed health benefits of C-PC intake. This review outlines how C-PC is produced and utilised and discusses the novel C-PC synthesis procedures and applications.

Production of phycocyanin : a pigment with applications in biology, biotechnology, foods and medicine

In the nearshore coastal waters along the Antarctic Peninsula, a recurrent shift in phytoplankton community structure, from diatoms to cryptophytes, has been documen­ ted. The shift was observed in consecutive years (1991–1996) during the austral summer and was correlated in time and space with glacial melt-water runoff and reduced surface water salinities. Elevated temperatures along the Peninsula will increase the extent of coastal melt-water zones and the seasonal prevalence of cryptophytes. This is significant because a change from diatoms to cryptophytes represents a marked shift in the size distribution of the phytoplankton community, which will, in turn, impact the zooplankton assemblage. Cryptophytes, because of their small size, are not grazed efficiently by Antarctic krill, a keystone species in the food web. An increase in the abundance and relative proportion of cryptophytes in coastal waters along the Peninsula will likely cause a shift in the spatial distribution of krill and may allow also for the rapid asexual proliferation of carbon poor gelatinous zooplankton, salps in particular. This scenario may account for the reported increase in the frequency of occurrence and abundance of large swarms of salps within the region. Salps are not a preferred food source for organisms that occupy higher trophic levels in the food web, specifically penguins and seals, and thus negative feedbacks to the ecology of these consumers can be anticipated as a consequence of shifts in phytoplankton community composition.

/pdf/alteration-of-the-food-web-along-the-antarctic-peninsula-in-39xoedz4ta.pdf

Alteration of the Food Web Along the Antarctic Peninsula in Response to a Regional Warming Trend

The effects of nitrate, phosphate, and iron starvation and resupply on photosynthetic pigments, selected photosynthetic proteins, and photosystem II (PSII) photochemistry were examined in the diatom Phaeodactylum tricornutum Bohlin (CCMP 1327). Although cell chlorophyll a (chl a) content decreased in nutrient-starved cells, the ratios of light-harvesting accessory pigments (chl c and fucoxanthin) to chl a were unaffected by nutrient starvation. The chl a-specific light absorpition coefficient (a*) and the functional absorption cross-section of PSII (σ) increased during nutrient starvation, consistent with reduction of intracellular self-shading (i.e. a reduction of the “package effect”) as cells became chlorotic. The light-harvesting complex proteins remained a constant proportion of total cell protein during nutrient starvation, indicating that chlorosis mirrored a general reduction in cell protein content. The ratio of the xanthophylls cycle pigments diatoxanthin and diadinoxanthin to chl a increased during nutrient starvation. These pigments are thought to play a photo-protective role by increasing dissipation of excitation energy in the pigment bed upstream from the reaction centers. Despite the increase in diatoxanthin and diadinoxanthin, the efficiency of PSII photochemistry, as measured by the ration of variable to maximum fluorescence (Fv/Fm) of dark-adapted cells, declined markedly under nitrate and iron starvation and moderately under phosphate starvation. Parallel to changes in Fv/Fm were decreases in abundance of the reaction center protein D1 consistent with damage of PSII reaction centers in nutrient-starved cells. The relative abundance of the carboxylating enzyme, ribulose bisphosphate carboxylase/oxygenase (RUBISCO), decreased in response to nitrate and iron starvation but not phosphate starvation. Most marked was the decline in the abundance of the small subunit of RUBISCO in nitrate-starved cells. The changes in pigment content and fluorescence characteristics were typically reversed within 24 h of resupply of the limiting nutrient.

Response of the photosynthetic apparatus of Phaeodactylum tricornutum (Bacillariophyceae) to nitrate, phosphate, or iron starvation

Harmful algal blooms in the Chesapeake Bay and coastal bays of Maryland, USA, are not a new phenomenon, but may be increasing in frequency and diversity. Outbreaks ofPfiesteria piscicida (Dinophyceae) were observed during 1997 in several Chesapeake Bay tributaries, while in 1998,Pfiesteria-related events were not found but massive blooms ofProrocentrum minimum (Dinophyceae) occurred. In 1999,Aureococcus anophagefferens (Pelagophyceae) developed in the coastal bays in early summer in sufficient densities to cause a brown tide. In 1997, toxicPfiesteria was responsible for fish kills at relatively low cell densities. In 1998 and 1999, the blooms ofP. minimum andA. anophagefferens were not toxic, but reached sufficiently high densities to have ecological consequences. These years differed in the amount and timing of rainfall events and resulting nutrient loading from the largely agricultural watershed. Nutrient loading to the eastern tributaries of Chesapeake Bay has been increasing over the past decade. Much of this nutrient delivery is in organic form. The sites of thePfiesteria outbreaks ranked among those with the highest organic loading of all sites monitored bay-wide. The availability of dissolved organic carbon and phosphorus were also higher at sites experiencingA. anophagefferens blooms than at those without blooms. The ability to supplement photosynthesis with grazing or organic substrates and to use a diversity of organic nutrients may play a role in the development and maintenance of these species. ForP. minimum andA. anophagefferens, urea is used preferentially over nitrate.Pfiesteria is a grazer, but also has the ability to take up nutrients directly. The timing of nutrient delivery may also be of critical importance in determining the success of certain species.

Harmful algal blooms in the Chesapeake and coastal bays of Maryland, USA: Comparison of 1997, 1998, and 1999 events

The nitrogen-rich phycobiliproteins are efficient light-harvesting pigments of cryptophytes, cyanobacteria, and rhodophytes. Whereas it is well established that certain cyanobacteria mobilize their phycobiliproteins in response to nitrogen deprivation, the effect of nitrogen stress on cryptophyte physiology has been studied only rarely. We compared the effects of nitrogen and phosphorus depletion on the biovolume, chemical composition, and pigment composition of the marine cryptophyte Pyrenomonas salina, grown in batch cultures under light-limiting and light-saturating conditions. Cellular phycoerythrin content declined during the late exponential growth phase in nitrogen-depleted cultures, and the cells were nearly devoid of phycoerythrin (< 3 % of the phycoerythrin content of nitrogen-replete cells) at the beginning of stationary growth. Phycoerythrin content also decreased during late exponential phase in phosphorus-depleted cultures, but these latter cells contained more than 10 times the phycoerythrin concentration of nitrogen-depleted cells at the same growth stage. Chlorophyll a content declined in nitrogen-depleted cultures, but at a slower rate than the decrease in phycoerythrin, such that the phycoerythrin to chlorophyll a ratio decreased by more than 95 O/O from the early exponential to early stationary growth phase. In nitrogen-depleted cultures grown at a low light intensity, the decline in phycoerythrin content preceded the decline in chlorophyll a content, and resulted in only slight changes in cellular nitrogen content and biovolume. These data indicate that phycoerythrin is preferentially lost from P. salina during nitrogen deficiency, and support the hypothesis that, similar to certain cyanobacteria, P. salina responds to nitrogen deprivation by mobilizing phycoerythrin in order to help sustain cellular nitrogen requirements.

/pdf/relative-effects-of-nitrogen-or-phosphorus-depletion-and-4xfony9rcm.pdf

Relative effects of nitrogen or phosphorus depletion and light intensity on the pigmentation, chemical composition, and volume of Pyrenomonas salina (Cryptophyceae)

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Relative effects of nitrogen or phosphorus depletion and light intensity on the pigmentation, chemical composition, and volume of Pyrenomonas salina (Cryptophyceae)