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Home , Phycoerythrin

and respiration

• Collectively, photosynthesis and respiration control bioelemental cycling.

Sunlight Photosynthesis:

6CO2 + 12H2OC6H12O6 + O2 + 6H2O + heat

Respiration:

C6H12O6 + 6O2 6CO2 + 6H2O + heat • Photosynthesis is initiated by the absorption of light energy by pigments or photochemically reactive proteins. The absorbed light energy is passed from the light harvesting pigments (antenna) to the photosynthetic reaction centers via the flow of electrons.

Sunlight Photosynthesis:

6CO2 + 12H2OC6H12O6 + O2 + 6H2O + heat Phytoplankton taxonomy

• Phytoplankton include single cells or organized colonies; the vast majority are very small (<10 µm): – Picoplankton: 0.2-2.0 µm – Nanoplankton: 2.0-20 µm – Microplankton: 20-200 µm

The picoplanktonic photosynthetic comprise a substantial component of plankton biomass and production in low nutrient systems. Identifying phytoplankton

• Cell biomarkers (pigments) • Microscopy/ • Nucleic acids (rDNA) • probes Major divisions and classes of photosynthetic plankton in the ocean • Prokaryotes – Cyanophyta (includes Prochlorophytes)

• Eukaryotes: – Chlorophyta (green algae); include 1 µm the following classes: Micromonas • Chlorophyceae • Prasinophceae • Euglenophyceae

– Chromophyta (brown algae); include the following classes: Pelagomonas • Chrysophyceae • Pelagophyceae • Prymnesiophyceae • Bacillariophyceae (diatoms) • Dinophyceae (dinoflagellates) • Cryptophyceae (crytophytes) • Phaeophyceae (phaeophytes) – Rhodophyta ()-mostly macrophytes Marine cyanobacteria

Prochlorococcus • Cyanobacteria: major groups of cyanobacteria in the oceans include: Prochlorococcus, , , Crocosphaera, Synechococcus Richelia

– Characteristics: unicellular, filamentous, colonial – 2 layer cell wall-inner murein and outer lipoprotein

– Some species fix N2

Richelia Trichodesmium Many images from: http://www.sb-roscoff.fr/Phyto/gallery/main.php?g2_itemId=19 Rhodophyta (Red Algae)

• Rhodophytes – In addition to Chl a, also contain phycoerythrin, , – Most marine Porphyridium representatives are macrophytes Rhodella Chlorophyta (green algae)

• Chlorophytes • Prasinophytes – Contain Chl b – Contain Chl b Nannochloris – Uncommon in – Predominately open ocean; unicellular mostly – Relatively freshwater. common, but not – In marine abundant in environment, ocean mostly tropical – Can be single (Hawaiian cells or colonies, coastal waters) coccoid, – Can be single biflagellated, or cells or colonies, quadri-flagellated coccoid or flagellated

Prasinophyceae Chromophyta (brown algae)

• Pelaophytes • Chrysophytes • Cryptophytes – Contain Chl c – Contain Chl c – Contain Chl c – Very common in – Relatively rare in – Contain open ocean. open ocean – Coccoid or – Mostly bi- alloxanthin monoflagellated flagellated – Contain (flagella of phycoerythrin or unequal length) phycocyanin – Flagellated unicells

Pelagomonas

Dictyocha Rhodomonas salina

Images from: http://planktonnet.sb-roscoff.fr/index.php#search Chromophyta (brown algae)-Cont.

• Prymnesiophytes • Bacillariophytes – Mainly biflagellates – Ubiquitous – Very common in – All contain Chl c and

open ocean carotenoidSkeltonmacsuD: 10/6OwrGyAdi – 2-5 µm fucoxanthin – Some species form – Rigid silica- impregnated cell wall CaCO3 plates 3 votes4.N/A (coccoliths) – Many form colonies – 2 prominent cell morphologies: centric and pennate

Emiliana huxleyi

Coscinodiscus Rhizosolenia Chromophyta (brown algae)-Cont.

Armored dinoflagellate-cellulose theca • Dinophytes Ceratium – Possess the carotenoid peridinin – Widely distributed (estuaries, open ocean) – Mostly unicellular and autotrophic, but colorless heterotrophs can Naked dinoflagellate also be abundant Gymnodinium – 2 flagella – Many are bioluminescent and some case toxic red tides blooms Active site of photosynthesis in eukaryotes is the . contain light harvesting pigments, electron carriers that capture energy for reducing power (NADPH2) and ATP, and enzymes that use

NADPH2 and ATP to fix CO2 and H2O to carbohydrate.

Components of the chloroplast: •Membranes • (lipids, , and protein)- contain the pigments and electron carriers •Stroma: gel-like matrix containing enzymes needed to fix CO2 (RUBISCO). • Different algal groups distinguished by arrangement of thylakoids

– Red algae: single thylakoids – Cryptophyta: thick pairs of thylakoids – Other groups tend to have 3 thylakoids stacked together – The green algae (and higher vascular plants) have 5-20 small diameter thylakoids stacked together

Cyanobacteria have thylakoids free in the cytoplasm with along the surface. Light harvesting photosynthetic pigments

• • •

• Recently discovered photoreceptor proteins (Proteorhodopsin and Bacteriorhodopsin) serve as proton pumps, but do not appear to harvest energy for oxygenic photosynthesis. Chlorophylls

• Cyclic tetrapyrole with a magnesium atom chelated in lacks the phytol the center of group the ring Phytol • All oxygen evolving photosynthetic plankton contain (peak absorption 450 and 660 nm) • (peak absorption 500 and 640 nm) found mostly found in Chlorphytes, Euglenophyta, and cyanobacteria • Chlorophyll c found in diatoms, dinoflagellates, chrysomonads, cryptophytes • Chl a, b, and c all absorb strongly in the red (between 440-450 nm) and blue wavelengths (~645-660 nm). The presence of Chl b and c increases the absorption between 450-650 nm. Carotenoids The double bonds absorb strongly in the short wavelength region of the visible spectrum • Isoprenoid compounds (lipids)-not water soluble, embedded in hydrophobic membranes. • Almost all chlorophyll and carotenoids occur as complexed proteins. • β- is found in all algal classes except the Cryptophytes Carotenoids

• Photosynthetic carotenoids participate in photosynthetic electron transport . • Non-photosynthetic carotenoids appear to protect photosynthetic reaction centers from oxidation via free radical scavenging

• Water soluble pigments that capture light energy and pass the energy to chlorophyll.

• Found in Rhodophytes (red algae), Cryptophytes, and Cyanobacteria – Red: phycoerythrin (red algae, often in cyanobacteria); phycoerythrocyanin – Blue: , allophycocyanins • Occur as aggregates, termed phycobilisomes, composed of 3 or more phycobiliproteins, that attach to the thylakoid. Summary of photosynthetic pigments; pigments in bold are diagnostic

Group Major pigments Prokaryotes Prochlorococcus Dinvinyl Chlorophyll a and b, monovinyl chlorophyll b, zeaxanthin Synechococcus Monovinyl chlorophyll a, zeaxanthin, phycoerythrin Eukaryotes Diatoms Monvinyl chlorophyll a, chlorophylls c1 and c2, fucoxanthin Prymnesiophytes Monovinyl chlorophyll a, chlorophylls c2 and c3, 19- hexanoyloxyfucoxanthin Pelagophytes Monovinyl chlorophyll a, chlorophylls c2 and c3, 19- butanoyloxyfucoxanthin Chrysophytes Monovinyl chlorophyll a, chlorophylls c1 and c2, fucoxanthin and violaxanthin Cryptophytes Monovinyl chlorophyll a, chlorophyll c2, alloxanthin Dinoflagellates Monovinyl chlorophyll a, chlorophyll c2, peridinin Prasinophytes Monovinyl chlorophyll a and b, prasinoxanthin Chlorophytes Monovinyl chlorophyll a and b, lutein Carotenoids and biliproteins extend the spectral region able to support plankton growth; thus light forms an important environmental control on microorganism evolution. Stomp et al. (2004) competing species coexistence ofmultiple providingstable capabilities, their lightharvesting differentiate microorganisms composition, phototrophic Through variationsinpigment Stomp et al.(2007) Stomp et

In vivo absorption spectra • Reaction center: the site in a photosystem where energy from absorbed light is transferred (via an electron) from one molecular (donor) to another (acceptor). • Reaction center chlorophyll becomes excited with the receipt of light energy. • To reduce this energy, the excited chlorophyll can transfer an electron to an acceptor.

• The majority of energy captured by reaction center chlorophyll is transferred via antenna pigments. • Summary of light reactions: 2H O + 2 NADP+ + 3 ADP +3 P O + 2 NADPH + 3 ATP 2 i 8 hν 2 2

• Summary of dark reactions:

CO2 fixation via the Calvin-Benson cycle

+ CO2 + 2 NADPH2 + 3 ATP H2O + (CH2O) + 3 ADP + 3Pi + 2 NADP

CO2 + 2 H2O(CH2O) + H2O + O2 8 hν Key enzymes for photosynthesis

• RUBISCO (1,5-bisphosphate carboxylase/oxygenase)-key enzyme in the Calvin-Benson cycle, incorporates CO2 into 3- phosphoglycerate. Most abundant protein on Earth.

• Carbonic anhydrase: converts CO2 to - - bicarbonate (HCO3 ) and vice versa. HCO3 is the most abundant form of inorganic carbon in seawater; most marine microorganisms take up - HCO3 and carbonic anhydrase dehydrates to CO2 near RUBISCO. Net and Gross Photosynthesis

• Net photosynthesis (PN): rate of photosynthesis excluding material lost to respiration in the light (RL).

• Gross photosynthesis (PG): The total amount of light energy converted into biochemical energy. Measured by evaluating total CO2 fixed or O2 evolved, including that lost to respiration.

PG = PN + RL

• Note that respiration also occurs in the dark (RD).

• Relatively straightforward to measure net or gross photosynthesis in pure cultures, but the oceans contain many organisms that contribute to respiration (e.g., bacteria, zooplankton). Primary Production

• Gross Primary Production: The rate of organic carbon production via the reduction of CO2 due to photosynthesis. • Net Primary Production: Gross primary production, less photoautotrophic respiration, integrated over time and depth. • Net Community Production: Gross primary production, less all autotrophic and heterotrophic losses due to respiration.

• Units for all measures of production: mgC m-2 d-1 What methods are used to measure aquatic primary production? • Typical rates of photosynthesis range between 0.2-2 µmol C L-1 d-1 or -1 -1 0.3-3 µmol O2 L d • Analytical sensitivity of measurements: -1 –CO2 by coulometry = 1 µmol C L -1 –O2 by Winkler titration = 0.01 µmol O2 L Most Common methods used to measure photosynthesis:

•CO2 assimilation: radio- or stable isotopes of carbon (14C or 13C) – developed by Steeman-Nielsen 1951.

• Changes in O2 concentration - developed by Gaarder and Gran 1927) • Oxygen isotope techniques (18O, 17O, 16O) O2 light-dark bottle approach Measures changes in oxygen concentrations in light and dark bottles following incubation period: •Light bottle = net community production (photosynthesis and respiration). •Dark bottle: community respiration. Light + Dark = Gross production

Several caveats: 1) assumes rate of respiration in dark = light. 2) requires conversion from

O2 to carbon units (photosynthetic quotient, PQ). 3) Requires incubation and confinement of samples.

PQ values can vary from 1.1 to 1.4 depending on nutrient environment and products of photosynthesis. 14 Examine assimilation of 14C (as C-bicarbonate bicarbonate) by photosynthetic plankton in the light. 14 - assimilation •Add C labeled HCO3 to bottles containing seawater; incubate and harvest plankton biomass by filtration. •Count (using scintillation counter) the amount of radioactive 14C assimilated into plankton biomass during incubation period.

Several caveats: 1) Always returns a positive result, even if net community production is negative. 2) Does not discriminate light and dark respiration. 3) Unclear whether net or gross photosynthesis is measured. 4) Generally ignores organic carbon produced and excreted or lost during incubation. 5) Requires incubation and confinement of samples Oxygen isotopes

18 • Addition of O labeled H2O: light bottle/dark bottle incubation approach; traces splitting of 18 H2O by photosynthesis yielding O2. By simultaneously examining changes in O2 concentrations, can determine gross primary production. • Triple oxygen (16O, 17O, 18O): aquatic photosynthesis has a characteristic fractionation of H2O in production of O2; can use the ratio of the different isotopes to derive photosynthetic O2 production. What factors limit primary production?

• Nutrients – Protein (~50% of cell biomass): H, C, O, N, S, metal co-factors – Lipid (~10% of cell biomass): H, C, O, P – Nucleic acids: H, C, N, O, P – Carbohydrates (~20% cell biomass): H, C, O • Light • Temperature