176 research outputs found
Direct estimation of functional PSII reaction center concentration and PSII electron flux on a volume basis: a new approach to the analysis of Fast Repetition Rate fluorometry (FRRf) data
No full textPhytoplankton primary productivity is most commonly measured by 14C assimilation although less direct methods, such as O2 exchange, have also been employed. These methods are invasive, requiring bottle incubation for up to 24 h. As an alternative, Fast Repetition Rate fluorometry (FRRf) has been used, on wide temporal and spatial scales within aquatic systems, to estimate photosystem II (PSII) electron flux per unit volume (JVPSII), which generally correlates well with photosynthetic O2 evolution. A major limitation of using FRRf arises from the need to employ an independent method to determine the concentration of functional photosystem II reaction centers ([RCII]); a requirement that has prevented FRR fluorometers being used, as stand-alone instruments, for the estimation of electron transport. Within this study, we have taken a new approach to the analysis of FRRf data, based on a simple hypothesis; that under a given set of environmental conditions, the ratio of rate constants for RCII fluorescence emission and photochemistry falls within a narrow range, for all groups of phytoplankton. We present a simple equation, derived from the established FRRf algorithm, for determining [RCII] from dark FRRf data alone. We also describe an entirely new algorithm for estimating JVPSII, which does not require determination of [RCII] and is valid for a heterogeneous model of connectivity among RCIIs. Empirical supporting evidence is presented. These data are derived from FRR measurements across a diverse range of microalgae, in parallel with independent measurements of [RCII]. Possible sources of error, particularly under nutrient stress conditions, are discussed
An integrated response of Trichodesmium erythraeum IMS101 growth and photo-physiology to Iron, CO<sub>2</sub>, and light intensity
No full textWe have assessed how varying CO2 (180, 380, and 720 μatm) and growth light intensity (40 and 400 μmol photons m-2 s-1) affected Trichodesmium erythraeum IMS101 growth and photophysiology over free iron (Fe') concentrations between 20 and 9,600 pM. We found significant iron dependencies of growth rate and the initial slope and maximal relative PSII electron transport rates (rPm). Under iron-limiting concentrations, high-light increased growth rates and rPm; possibly indicating a lower allocation of resources to iron-containing photosynthetic proteins. Higher CO2 increased growth rates across all iron concentrations, enabled growth to occur at lower Fe' concentrations, increased rPm and lowered the iron half saturation constants for growth (Km). We attribute these CO2 responses to the operation of the CCM and the ATP spent/saved for CO2 uptake and transport at low and high CO2, respectively. It seems reasonable to conclude that T. erythraeum IMS101 can exhibit a high degree of phenotypic plasticity in response to CO2, light intensity and iron-limitation. These results are important given predictions of increased dissolved CO2 and water column stratification (i.e., higher light exposures) over the coming decades.</p
A model of photosynthesis and photo-protection based on reaction center damage and repair
No full textPhytoplankton photosynthesis under the rapidly fluctuating irradiance which results from turbulent mixingthrough the vertical light gradient is poorly understood. Ship-based measurements often apply the fast repetitionrate fluorescence (FRRF) technique in situ or in vivo to gauge the physiological state of the phytoplanktoncommunity and infer some of the physical properties of the water column (such as mixing time scales). We describethe development and validation of a model of photosynthetic electron turnover at photosystemII with considerationof downstream limitation, based on the redox state of photosystem II. We also include empirical formulations forslower processes such as photo-protection (from nonphotochemical quenching) and photo-inhibition. Byconfronting the simple model with laboratory data for Dunaliella tertiolecta, we were able to refine the model sothat it faithfully produced rates of photosynthetic electron transfer determined by FRR fluorescence. Further, wewere able to validate the model estimates of linear photosynthetic electron transfer rates against completelyindependent measurements obtained using 14C-bicarbonate assimilation in photosynthesis-light curves
Interpretation of fast repetition rate (FRR) fluorescence: signatures of phytoplankton community structure versus physiological state
No full textIntroduction of active chlorophyll a fluorescenceprotocols, in particular fast repetition rate(FRR) fluorometry, to oceanography and limnology15 yr ago has enabled rapid assessment of photosyntheticphysiology in situ. The FRR protocol generatessimultaneous measurements of Photosystem II (PSII)effective absorption cross sections (termed ?PSII) andphotochemical efficiency (termed Fv/Fm). Both Fv/Fmand ?PSII measurements have been utilised to examinethe effects of physiological stress on the photosyntheticapparatus of phytoplankton in an ever growing numberof fluorescence-based studies. However, it is nowbecoming clearer that in situ values of Fv/Fm and ?PSIIalso contain taxonomic information. Here, we presenta synthesis of previously unpublished and publisheddata, which show that Fv/Fm and ?PSII vary principallywith broad-scale changes in community structure.These patterns observed in situ conform to trendsobserved in laboratory-grown cultures of a range ofphytoplankton taxa. The magnitudes of variability inFv/Fm and ?PSII driven by changes in phytoplanktoncommunity structure often exceed that induced bynutrient limitation (as determined from controllednutrient addition experiments). An exception to thisgeneral trend occurs in high-nutrient, low-chlorophylla (HNLC) regions, where strong phenotypic changesin Fv/Fm and ?PSII have been repeatedly demonstratedon relief of iron limitation. Overall, FRR fluorescencemeasurements of both Fv/Fm and ?PSII in natural populationsrepresent a combination of the taxonomic ‘signature’(values of Fv/Fm and ?PSII determined by thetaxa present) within the phytoplankton communitythat is further modified according to the (photo-) physiologicalstatus. As such, fluorescence-based investigationsof mixed populations must account for potentialvariations in phytoplankton community structure beforeinterpretations of physiological status are made
Plasticity in the proteome of Emiliania huxleyi CCMP 1516 to extremes of light is highly targeted
No full textSummary
Optimality principles are often applied in theoretical studies of microalgal ecophysiology to predict changes in allocation of resources to different metabolic pathways, and optimal acclimation is likely to involve changes in the proteome, which typically accounts for > 50% of cellular nitrogen (N).
We tested the hypothesis that acclimation of the microalga Emiliania huxleyi CCMP 1516 to suboptimal vs supraoptimal light involves large changes in the proteome as cells rebalance the capacities to absorb light, fix CO2, perform biosynthesis and resist photooxidative stress.
Emiliania huxleyi was grown in nutrient‐replete continuous culture at 30 (LL) and 1000 μmol photons m−2 s−1 (HL), and changes in the proteome were assessed by LC‐MS/MS shotgun proteomics. Changes were most evident in proteins involved in the light reactions of photosynthesis; the relative abundance of photosystem I (PSI) and PSII proteins was 70% greater in LL, light‐harvesting fucoxanthin–chlorophyll proteins (Lhcfs) were up to 500% greater in LL and photoprotective LI818 proteins were 300% greater in HL.
The marked changes in the abundances of Lhcfs and LI818s, together with the limited plasticity in the bulk of the E. huxleyi proteome, probably reflect evolutionary pressures to provide energy to maintain metabolic capabilities in stochastic light environments encountered by this species in nature.
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Assessment of photosynthesis in a spring cyanobacterial bloom by use of a fast repetition rate fluorometer
No full textIron limits primary productivity during spring bloom development in the central North Atlantic
No full textWe present in situ biophysical measurements and bioassay experiments that demonstrate iron limitation of primary productivity during the spring bloom in the central North Atlantic. Mass balance calculations indicate that nitrate drawdown is iron (Fe)-limited and that aeolian Fe supply to this region cannot support maximal phytoplankton growth during the bloom. Using a simple simulation model, we show that relief of Fe limitation during the spring bloom can increase nitrate drawdown and, hence, new primary production, by 70%. We conclude that the episodic nature of iron supplied by dust deposition is an important factor controlling the dynamics of the spring bloom. From this, we hypothesize that variability in the timing and magnitude of the spring bloom in response to aeolian Fe supply will affect carbon drawdown and food web dynamics in the central North Atlantic
Quantifying integrated proteomic responses to iron stress in the globally important marine diazotroph trichodesmium
No full textTrichodesmium is a biogeochemically important marine cyanobacterium, responsible for a significant proportion of the annual ‘new’ nitrogen introduced into the global ocean. These non-heterocystous filamentous diazotrophs employ a potentially unique strategy of near-concurrent nitrogen fixation and oxygenic photosynthesis, potentially burdening Trichodesmium with a particularly high iron requirement due to the iron-binding proteins involved in these processes. Iron availability may therefore have a significant influence on the biogeography of Trichodesmium. Previous investigations of molecular responses to iron stress in this keystone marine microbe have largely been targeted. Here a holistic approach was taken using a label-free quantitative proteomics technique (MSE) to reveal a sophisticated multi-faceted proteomic response of Trichodesmium erythraeum IMS101 to iron stress. Increased abundances of proteins known to be involved in acclimation to iron stress and proteins known or predicted to be involved in iron uptake were observed, alongside decreases in the abundances of iron-binding proteins involved in photosynthesis and nitrogen fixation. Preferential loss of proteins with a high iron content contributed to overall reductions of 55–60% in estimated proteomic iron requirements. Changes in the abundances of iron-binding proteins also suggested the potential importance of alternate photosynthetic pathways as Trichodesmium reallocates the limiting resource under iron stress. Trichodesmium therefore displays a significant and integrated proteomic response to iron availability that likely contributes to the ecological success of this species in the ocean
The trade-off between the light-harvesting and photoprotective functions of fucoxanthin-chlorophyll proteins dominates light acclimation in Emiliania huxleyi (clone CCMP 1516)
No full textMechanistic understanding of the costs and benefits of photoacclimation requires knowledge of how photophysiology is affected by changes in the molecular structure of the chloroplast.We tested the hypothesis that changes in the light dependencies of photosynthesis, nonphotochemical quenching and PSII photoinactivation arises from changes in the abundances of chloroplast proteins in Emiliania huxleyi strain CCMP 1516 grown at 30 (Low Light; LL) and 1000 (High Light; HL) µmol photons m-2 s-1 photon flux densities.Carbon-specific light-saturated gross photosynthesis rates were not significantly different between cells acclimated to LL and HL. Acclimation to LL benefited cells by increasing biomass-specific light absorption and gross photosynthesis rates under low light, whereas acclimation to HL benefited cells by reducing the rate of photoinactivation of PSII under high light. Differences in the relative abundances of proteins assigned to light-harvesting (Lhcf), photoprotection (LI818-like), and the photosystem II (PSII) core complex accompanied differences in photophysiology: specifically, Lhcf:PSII was greater under LL, whereas LI818:PSII was greater in HL.Thus, photoacclimation in E. huxleyi involved a trade-off amongst the characteristics of light absorption and photoprotection, which could be attributed to changes in the abundance and composition of proteins in the light-harvesting antenna of PSII
Relative influence of nitrogen and phosphorous availability on phytoplankton physiology and productivity in the oligotrophic sub-tropical North Atlantic Ocean
No full textNutrient addition bioassay experiments were performed in the low-nutrient, low-chlorophyll oligotrophic subtropical North Atlantic Ocean to investigate the influence of nitrogen (N), phosphorus (P), and/or iron (Fe) on phytoplankton physiology and the limitation of primary productivity or picophytoplankton biomass. Additions of N alone resulted in 1.5–2 fold increases in primary productivity and chlorophyll after 48 h, with larger (~threefold) increases observed for the addition of P in combination with N (NP). Measurements of cellular chlorophyll contents permitted evaluation of the physiological response of the photosynthetic apparatus to N and P additions in three picophytoplankton groups. In both Prochlorococcus and the picoeukaryotes, cellular chlorophyll increased by similar amounts in N and NP treatments relative to all other treatments, suggesting that pigment synthesis was N limited. In contrast, the increase of cellular chlorophyll was greater in NP than in N treatments in Synechococcus, suggestive of NP co-limitation. Relative increases in cellular nucleic acid were also only observed in Synechococcus for NP treatments, indicating co-limitation of net nucleic acid synthesis. A lack of response to relief of nutrient stress for the efficiency of photosystem II photochemistry, Fv :Fm, suggests that the low nutrient supply to this region resulted in a condition of balanced nutrient limited growth, rather than starvation. N thus appears to be the proximal (i.e. direct physiological) limiting nutrient in the oligotrophic sub-tropical North Atlantic. In addition, some major picophytoplankton groups, as well as overall autotrophic community biomass, appears to be co-limited by N and P
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