PHOTOACCLIMATION OF PHOTOSYNTHESIS IRRADIANCE RESPONSE CURVES AND PHOTOSYNTHETIC PIGMENTS IN MICROALGAE AND CYANOBACTERIA1

The photosynthesis‐irradiance response (PE) curve, in which mass‐specific photosynthetic rates are plotted versus irradiance, is commonly used to characterize photoacclimation. The interpretation of PE curves depends critically on the currency in which mass is expressed. Normalizing the light‐limited rate to chl a yields the chl a‐specific initial slope (α^chl). This is proportional to the light absorption coefficient (a^chl), the proportionality factor being the photon efficiency of photosynthesis (φ_m). Thus, α^chl is the product of a^chl and φ_m. In microalgae α^chl typically shows little (<20%) phenotypic variability because declines of φ_m under conditions of high‐light stress are accompanied by increases of a^chl. The variation of α^chl among species is dominated by changes in a^chl due to differences in pigment complement and pigment packaging. In contrast to the microalgae, α^chl declines as irradiance increases in the cyanobacteria where phycobiliproteins dominate light absorption because of plasticity in the phycobiliprotein:chl a ratio. By definition, light‐saturated photosynthesis (P_m) is limited by a factor other than the rate of light absorption. Normalizing P_m to organic carbon concentration to obtain P_m^C allows a direct comparison with growth rates. Within species, P_m^C is independent of growth irradiance. Among species, P_m^C covaries with the resource‐saturated growth rate. The chl a:C ratio is a key physiological variable because the appropriate currencies for normalizing light‐limited and light‐saturated photosynthetic rates are, respectively, chl a and carbon. Typically, chl a:C is reduced to about 40% of its maximum value at an irradiance that supports 50% of the species‐specific maximum growth rate and light‐harvesting accessory pigments show similar or greater declines. In the steady state, this down‐regulation of pigment content prevents microalgae and cyanobacteria from maximizing photosynthetic rates throughout the light‐limited region for growth. The reason for down‐regulation of light harvesting, and therefore loss of potential photosynthetic gain at moderately limiting irradiances, is unknown. However, it is clear that maximizing the rate of photosynthetic carbon assimilation is not the only criterion governing photoacclimation.     

DIEL VARIATIONS IN OPTICAL PROPERTIES OF IMANTONIA ROTUNDA (HAPTOPHYCEAE) AND THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE) EXPOSED TO DIFFERENT IRRADIANCE LEVELS1

Diel variations of cellular optical properties were examined for cultures of the haptophyte Imantonia rotunda N. Reynolds and the diatom Thalassiosira pseudonana (Hust.) Hasle et Heimdal grown under a 14:10 light:dark (L:D) cycle and transferred from 100 μmol photons · m^?2 · s^?1 to higher irradiances of 250 and 500 μmol photons · m^?2 · s^?1. Cell volume and abundance, phytoplankton absorption coefficients, flow‐cytometric light scattering and chl fluorescence, and pigment composition were measured every 2 h over a 24 h period. Results showed that cell division was more synchronous for I. rotunda than for T. pseudonana. Several variables exhibited diel variability with an amplitude >100%, notably mean cell volume for the haptophyte and photoprotective carotenoids for both species, while optical properties such as flow‐cytometric scattering and chl a–specific phytoplankton absorption generally showed <50% diel variability. Increased irradiance induced changes in pigments (both species) and mean cell volume (for the diatom) and amplified diel variability for most variables. This increase in amplitude is larger for pigments (factor of 2 or more, notably for cellular photoprotective carotenoid content in I. rotunda and for photosynthetic pigments in T. pseudonana) than for optical properties (a factor of 1.5 for chl a–specific absorption, at 440 nm, in I. rotunda and a factor of 2 for the absorption cross‐section and the chl a–specific scattering in T. pseudonana). Consequently, diel changes in optical properties and pigmentation associated with the L:D cycle and amplified by concurrent changes in irradiance likely contribute significantly to the variability in optical properties observed in biooptical field studies.     

PHOTOSYNTHETIC FUNCTION IN DUNALIELLA TERTIOLECTA (CHLOROPHYTA) DURING A NITROGEN STARVATION AND RECOVERY CYCLE

Phytoplankton can be exposed to periods of N starvation with episodic N resupply. N starvation in Dunaliella tertiolecta (Butcher) measured over 4 days was characterized by slow reduction in cell chl and protein content and chl/carotenoid ratio and a decline in photosynthetic capacity and maximum quantum yield of photosynthesis (F_v/F_m). In the early stages of N starvation, cell division was maintained despite reduction in cellular chl. Chl content was more sensitive than carotenoids to N deprivation, and cellular chl a was maintained preferentially over chl b under N starvation. NO₃^? resupply stimulated rapid and complete recovery of F_v/F_m (from 0.4 to 0.7) within 24 h and commencement of cell division after 10 h, although N‐replete levels of cell chl and protein were not reestablished within 24 h. Recovery of F_v/F_m was correlated with increases in cell chl and protein and was more related to increases in F_m than to changes in F₀. Recovery of F_v/F_m was biphasic with a second phase of recovery commencing 4–6 h after resupply of NO₃^?. Uptake of NO₃^? from the external medium and the recovery of F_v/F_m, cell chl, and protein were inhibited when either cytosolic or chloroplastic protein synthesis was inhibited by cycloheximide or lincomycin, respectively; a time lag observed before maximum NO₃^? uptake was consistent with synthesis of NO₃^? transporters and assimilation enzymes. When both chloroplastic and cytosolic translation was inhibited, F_v/F_m declined dramatically. Dunaliella tertiolecta demonstrated a capacity to rapidly reestablish photosynthetic function and initiate cell division after N resupply, an important strategy in competing for limiting inorganic N resources.     

The pigment composition of Phaeocystis antarctica (Haptophyceae) under various conditions of light,temperature, salinity,and iron

The pigment composition of Phaeocystis antarctica was monitored under various conditions of light, temperature, salinity, and iron. 19′‐Hexanoyloxyfucoxanthin (Hex‐fuco) always constituted the major light‐harvesting pigment, with remarkably stable ratios of Hex‐fuco‐to‐chl a under the various environmental conditions. Increased pigment‐to‐chl a ratios at low irradiance confirmed the light‐harvesting function of Fucoxanthin (Fuco), 19′‐Hexanoyloxy‐4‐ketofucoxanthin (Hex‐kfuco), 19′‐butanoyloxyfucoxanthin (But‐fuco), and chl c2 and c3. Increased pigment‐to‐chl a ratios at high irradiance, low iron concentrations, and to a lesser extent at high salinity confirmed the photoprotective function of diadinoxanthin, diatoxanthin, and ß,ß‐carotene. Pigment ratios were not always according to expectations. The consistent increase in But‐fuco/chl at high temperature, high salinity, and low iron suggests a role in photoprotection rather than in light harvesting. Low Hex‐kfuco/chl ratios at high salinity were consistent with a role as light harvester, but the high ratios at high temperature were not, leaving the function of Hex‐kfuco enigmatic. Dedicated experiments were performed to test whether or not the light‐harvesting pigment Fuco could be converted into its structural relative Hex‐fuco, and vice versa, in response to exposure to light shifts. Rapid conversions could not be confirmed, but long‐term conversions cannot be excluded. New pigment ratios are proposed for chemotaxonomic applications. The ratios will improve pigment‐based diagnosis of algal species in waters dominated by P. antarctica.     

CARBON SOURCE DEPENDENCE OF THE RATIO OF δ‐AMINOLEVULINIC ACID BIOSYNTHESIS VIA THE C5 AND SHEMIN PATHWAYS IN EUGLENA GRACILIS (EUGLENOPHYCEAE)1

The ratio of two biosynthetic pathways was estimated, the C5 and Shemin pathways, to δ‐aminolevulinic acid (ALA, a biosynthetic intermediate of tetrapyrrole) from the ¹³C‐enrichment ratios (¹³C‐ER) at the carbon atoms of chl a (after conversion to methyl pheophorbide a) biosynthesized by Euglena gracilis G. A. Klebs when l ‐[3‐¹³C]alanine was used as a carbon source. On the basis of these estimations, we confirmed that ALA was efficiently biosynthesized via both the C5 and Shemin pathways in the plastids of E. gracilis, and we determined that the ratio of ALA biosynthesis via the Shemin pathway was increased in the ratio of 14%–67%, compared with that in our previous d ‐[1‐¹³C]glucose feeding experiment ( Iida et al. 2002 ). This carbon source dependence of the contributions of the two biosynthetic pathways might be related to activation of gluconeogenesis by the amino acid substrate. The methoxy carbon of the methoxycarbonyl group at C‐13² of chl a was labeled with the ¹³C‐carbon of l ‐[methyl‐¹³C]methionine derived from l ‐[3‐¹³C]alanine via [2‐¹³C]acetyl coenzyme A (CoA), through the atypical tricarboxylic acid (TCA) cycle, gluconeogenesis, and l‐ [3‐¹³C]serine. The phytyl moiety of chl a was also labeled on C‐P2, C‐P3¹, C‐P4, C‐P6, C‐P7¹, C‐P8, C‐P10, C‐P11¹, C‐P12, C‐P14, C‐P15¹, and C‐P16 from ¹³C‐isoprene (2‐[1,2‐methyl,3‐¹³C₃]methyl‐1,3‐butadiene) generated from l ‐[3‐¹³C]alanine via [2‐¹³C]acetyl CoA.     

BIO-OPTICAL CHARACTERISTICS AND PHOTOADAPTIVE RESPONSES IN THE TOXIC AND BLOOM-FORMING DINOFLAGELLATES GYRODINIUM AUREOLUM,GYMNODINIUM GALATHEANUM,AND TWO STRAINS OF PROROCENTRUM MINIMUM1

Photoadaptive responses in the toxic and bloom-forming dinoflagellates Gyrodinium aureolum Hulbert, Gymnodinium galatheanum Braarud, and two strains of Prorocentrum minimum (Pavillard)Schiller were evaluated with respect to pigment composition, light-harvesting characteristics, carbon and nitrogen contents, and growth rates in shade- and light-adapted cells. The two former species were grown at scalar irradiances of 30 and 170 μmol · m ^?2 at a 12-h daylength at 20° C. The two strains of P. minimum were grown at 35 and 500 μmol. m^?2· s^?1 at a 2-h daylength at 20° C. For the first time, chlorophyll (chl) c₃, characteristic of several bloom-forming prymnesiophytes, was detected in G. aureolum and G. galatheanum. Photoadaptional status affected the pigment composition strongly, and the interpretation of the variation depended on whether the pigment composition was normalized per cell, carbon, or chl a. Species-specific and photoadaptional differences in chl a-specific absorption (°a_c, 400–700 nm) and chl a-normalized fluorescence excitation spectra of photosystem II fluorescence with or without addition of DCMU (°F and °F_DCMU 400–700 nm) were evident. Gyrodinium aureolum and G. galatheanum exhibited in vivo spectral characteristics similar to chl c₃-containing prymnesiophytes in accordance with their similar pigmentation. Prorocentrum minimum had in vivo absorption and fluorescence characteristics typical for peridinin-containing dinoflagellates. Species-specific differences in in vivo absorption were also observed as a function of package effect vs. growth irradiance. This effect could be explained by differences in intracellular pigment content, cell size/shape, and chloroplast morphology/numbers. Light- and shade-adapted cells of P. minimum contained 43 and 17% of photoprotective carotenoids (diadino + diatoxanthin) relative to chl a, respectively. The photoprotective function of these carotenoids was clearly observed as a reduction in °F and °F ^DCMU at 400–540 nm compared to °ac in light-adapted cells of P. minimum. Spectrally weighted light absorption (normalized to chl a and carbon, 400–700 nm) varied with species and growth conditions. The use of quantum-corrected and normalized fluorescence excitation spectra with or without DCMU-treated cells to estimate photosynthetically usable light is discussed. The usefulness of in vitro absorption and fluorescence excitation spectra for estimation of the degradation status of chl a and the ratio of chl a to total pigments is also discussed.     

PHOTOSYNTHETIC PIGMENT COMPOSITION IN THE PRIMITIVE GREEN ALGA MESOSTIGMA VIRIDE (PRASINOPHYCEAE): PHYLOGENETIC AND EVOLUTIONARY IMPLICATIONS1

The photosynthetic pigment composition of Mesostigma viride Lauterborn, a primitive green alga, was determined. This alga contained chl a and b, lycopene, lutein, siphonaxanthin, γ‐carotene, β‐carotene, antheraxanthin, violaxanthin, neoxanthin, and two novel carotenoid fatty acid esters, siphonaxanthin C12:0 ester and siphonaxanthin C14:0 ester. The esters were saturated, whereas all previously identified siphonaxanthin and loroxanthin esters have been mono‐unsaturated (trans‐Δ2). Neoxanthin was the all‐trans form. This is the first such case detected in the chloroplasts of green plants. The 9′‐cis form of neoxanthin is believed to be universally present in the chloroplasts of green plants (Streptophyta and Chlorophyta) and is a precursor of abscisic acid. However, the 9′‐cis form was not found in M. viride. Based on these results, we discuss the phylogenetic implications and early evolution of the antenna pigment system in green plants.     

AMMONIUM AND UV RADIATION STIMULATE THE ACCUMULATION OF MYCOSPORINE‐LIKE AMINO ACIDS IN PORPHYRA COLUMBINA (RHODOPHYTA) FROM PATAGONIA,ARGENTINA1

The combined effects of ammonium concentration and UV radiation on the red alga Porphyra columbina (Montagne) from the Patagonian coast (Chubut, Argentina) was determined using short‐term (less than a week) experimentation. Discs of P. columbina were incubated with three ammonium concentrations (0, 50, and 300 μM NH₄Cl) in anilluminated chamber (PAR=300 μmol photons·m^?2·s^?1, UVA=15 W·m^?2, UVB=0.7 W·m^?2) at 15°C. Algae incubated at 300 μM ammonium showed a significant increase (P<0.05) in the concentration of mycosporine‐like amino acids (MAAs) compared with the initial value or with the other ammonium treatments. The increase of MAAs was, however, a function of the quality of irradiance received, with a higher increase in samples exposed to UVA compared with UVB (29% and 5% increase, respectively). However, UVB radiation was more effective in inducing MAA synthesis per unit energy received by the algae. Samples exposed to PAR only had an intermediate increase in MAA concentration of 16%. Chl a concentration decreased through the incubation with the greatest decrease at high ammonium concentration. Phycobiliprotein (BP) decreased through time with the smallest decrease occurring at high ammonium concentration. Photoinhibition (as a decrease of optimal quantum yield) was significantly greater under nitrogen‐deprived conditions than that under replete ammonium levels. Maximal gross photosynthesis (GP_max), as oxygen evolution, and maximal electron transport rate (ETR_max), as chl fluorescence, increased with the ammonium concentration. Positive relationships between maximal GP or ETR and pigment ratios (BP/chl a and MAAs/chl a) and negative relationships with chl a concentration were found.     

THE RESPONSE OF GROWTH AND BIOCHEMICAL COMPOSITION TO VARIATIONS IN DAYLENGTH, TEMPERATURE, AND IRRADIANCE IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)

The relationships between the growth rate of the marine diatom Thalassiosira pseudonana (Hustedt) and irradiance, daylength, and temperature were determined in nutrient-sufficient semicontinuous cultures. The initial slopes of the growth versus total daily irradiance curves were not affected by temperature or daylength. Growth versus irradiance was best modeled as a hyperbolic function at short daylengths and better modeled as an exponential function at longer daylengths. The maximum or light-saturated growth rates at each daylength were modeled as a hyperbolic function of daylength. This model was extended in a novel manner to include temperature dependence providing a framework that can be used to interpret other experimental data on growth rate versus daylength. The resulting model should be useful in global models of phytoplankton growth. Carbon, nitrogen, and chl a quotas were influenced by daylength, irradiance, and temperature. Both C and N quotas were positive exponential functions of irradiance, whereas N and chl a quotas were significantly greater for cells grown at the lower temperature. The ratio chl a :C quota (chl a :Q_c) was a strong negative exponential function of total daily irradiance. Cells grown at 10° C had significantly greater chl a :Q_c ratios than those grown at 18° C, and daylength also had a significant positive influence on chl a :Q_c. The apparent effect of daylength on chl a :Q_c was removed by standardizing chl a :Q_c to growth rate (μ), resulting in a temperature-dependent relationship between chl a :Q_c·μ⁻¹ and irradiance that accounted for 95% of the variation in the data.     

UV radiation and phosphorus interact to influence the biochemical composition of phytoplankton

1. Numerous laboratory studies have shown that food quality is suboptimal for zooplankton growth. However, little is known about how food quality is affected by the interaction of potential global change factors in natural conditions. Using field enclosures in a high altitude Spanish lake, seston was exposed to increasing phosphorus (P) concentrations in the absence and presence of UV radiation (UVR) to test the hypothesis that interactions between these factors affected the biochemical and stoichiometric composition of seston in ways not easily predicted from studies of single factors. 2. Phosphorus enrichment increased the content of total fatty acids (TFA), ω3‐polyunsaturated fatty acids (ω3‐PUFA) and chlorophyll‐a : carbon (Chl‐a : C) and C : N ratios in seston. The pronounced increase in ω3‐PUFA was largely explained by the enhancement of 18:3n‐3 (α‐linolenic acid). In contrast, P‐enrichment lowered the content of highly unsaturated fatty acids (HUFA), the HUFA : PUFA ratio and, at high P loads, seston C : P ratio. Although phytoplankton assemblages dominated by Chlorophytes were not rich in HUFA, seston in the control had substantially higher 20:4n‐6 (arachidonic acid, ARA) content (79% of HUFA) than did P‐enriched enclosures. 3. The UVR increased the content of ω3‐PUFA and TFA in seston at the two ends of the trophic gradient generated at ambient and high concentrations of P, but decreased seston C : P and HUFA at all points on this gradient. ARA was not detected in the presence of UVR. 4. The interaction between P and UVR was significant for seston HUFA and C : P ratios, indicating that the effect of UVR in reducing HUFA (decreased food quality) and C : P ratios (enhanced food quality) was most pronounced at the low nutrient concentrations characteristic of oligotrophic conditions and disappeared as P increased. Therefore, any future increase in UVR fluxes will probably affect most strongly the food quality of algae inhabiting oligotrophic pristine waters although, at least in the Mediterranean region, these effects could be offset by greater deposition of P from the atmosphere.     

Carotenoid-to-chlorophyll ratio as a proxy for assay of total fatty acids and arachidonic acid content in the green microalga Parietochloris incisa

The relationships between pigment (carotenoid and chlorophyll) content with accumulation of total fatty acids (TFA) and arachidonic acid (AA) were studied in the green microalga Parietochloris incisa (Trebouxiophyceae, Chlorophyta) grown under different PFDs (35, 200, and 400 μmol photons m⁻² s⁻¹) and nitrogen availabilities. The growth of P. incisa under higher light and nitrogen deficiency was accompanied by accumulation of FA, an increase in carotenoid and a decline in chlorophyll content. It was found that the carotenoid-to-chlorophyll ratio (but not the individual pigment content) correlates closely with the volumetric content of both TFA and AA. Analysis of scattering-compensated absorption spectra of P. incisa suspensions revealed their tight relationship in the blue-green range of the spectrum with the carotenoid-to-chlorophyll ratio, TFA, and AA content. These findings allowed the development of algorithms for the non-destructive assay of TFA and AA in cell suspensions in the ranges of 0.09–3.04 and 0.04–1.7 μg mL⁻¹, with accuracy of 0.06 and 0.01 μg mL⁻¹, respectively, via analytically measured carotenoid-to-chlorophyll ratio and using the ratio of absorption coefficients at 510 and 678 nm, with accuracy of 0.07 and 0.02 μg mL⁻¹, respectively. The feasibility of obtaining essential spectral information concerning the physiological condition of P. incisa using a standard spectrophotometer is also shown.     

STRATEGIES AND RATES OF PHOTOACCLIMATION IN TWO MAJOR SOUTHERN OCEAN PHYTOPLANKTON TAXA: PHAEOCYSTIS ANTARCTICA (HAPTOPHYTA) AND FRAGILARIOPSIS CYLINDRUS (BACILLARIOPHYCEAE)1

We investigated rates and mechanisms of photoacclimation in cultures of Phaeocystis antarctica G. Karst. and Fragilariopsis cylindrus (Grunow) Willi Krieg, phytoplankton taxa that each dominate distinct areas of the Ross Sea, Antarctica. Both P. antarctica and F. cylindrus acclimated to increases in irradiance by reducing the effective size of the pigment antenna (σPSII) via xanthophyll‐cycle activity and reductions in chl. While enhanced photoprotection facilitated increases in specific growth rate and eventually led to higher light‐saturated photosynthetic rates (P^cell_m) in P. antarctica, increases in those variables were much smaller in F. cylindrus. In response to a lower irradiance, relaxation of xanthophyll‐cycle activity led to an increase in σPSII in both taxa, which occurred much more slowly in F. cylindrus. A surprising increase in specific growth rate over the first 36 h of acclimation in P. antarctica may have facilitated the significant reductions in P^cell_m observed in that taxon. In general, P. antarctica acclimated more quickly to changes in irradiance than F. cylindrus, exhibited a wider range in photosynthetic rates, but was more susceptible to photoinhibition. This acclimation strategy is consistent with growth in deeply mixed water columns with variations in irradiance that allow time for repair. In contrast, the slower acclimation rates, extensive photoprotection, and low photoinhibition exhibited by F. cylindrus suggest that it does not require the same period for repair as P. antarctica and is best suited for growth in habitats with relatively uniform irradiance, such as shallow mixed layers or sea ice.     

OCCURRENCE OF LOROXANTHIN,LOROXANTHIN DECENOATE,AND LOROXANTHIN DODECENOATE IN TETRASELMIS SPECIES (PRASINOPHYCEAE,CHLOROPHYTA)1

The pigment composition of six species of Tetraselmis (Prasinophyceae) was analyzed using improved HPLC methods. All pigment extracts showed three peaks corresponding to unknown carotenoids. The isolated pigments were analyzed using UV–Vis spectroscopy, electrospray ionization–mass spectrometry (ESI–MS), and when carotenoid esters were suspected, gas chromatography–mass spectrometry (GC–MS) of the methyl ester and dimethyloxazoline derivative of the corresponding fatty acid. The new pigments were determined to be loroxanthin, loroxanthin 19‐(2‐decenoate), and loroxanthin 19‐(2‐dodecenoate); this is the first time these pigments have been described in the genus Tetraselmis. Moreover, this is the first report of esterification of 2‐decenoic acid to loroxanthin. The relative contents of these pigments depended on the light regime, with the lowest proportions measured at the highest photon flux density assayed. The implications of the identification of these pigments in the genus Tetraselmis for the pigment types previously described in the class Prasinophyceae are discussed.     

THE RELATIONSHIP OF LIPIDS WITH LIGHT AND CHLOROPHYLL MEASUREMENTS IN FRESHWATER ALGAE AND PERIPHYTON1

Lipid content and lipid class composition were determined in stream periphyton and the filamentous green algae Cladophora sp. and Spirogyra sp, Sterols and phospholipids were compared to chlorophyll a (chl a) as predictors of biomass for stream periphyton and algae. Chlorophyll a, phospholipids, and sterols were each highly correlated with ash-free dry mass (AFDM) (r² > 0.98). Stream periphyton exposed naturally to high light (HL) and low light (LL) had chl a concentrations (μg chl a-mg^?1AFDM) of 7.9± 0.7 and 12.4 ± 2.9, respectively, while the sterol concentrations of these HL and LL stream periphyton (1.6 ± 0.4) were not significantly different (P > 0.05). Periphyton exposed to an irradiance of 300 μmol photons·m^?2s^?1 in the laboratory for 60 h had 5.6 ± 0.55 μg chl a·mg^?1 AFDM, but the same periphyton exposed to 2% incident light for the same amount of time had 11.0 ± 0.56 μg chl a·mg^?1 AFDM. Sterol concentrations in these periphyton communities remained unchanged (1.5 ± 0.3 μg·mg^?1AFDM), Similar results (i.e. changes in chl a but stability of sterol concentrations in response to irradiance changes) were also found for Cladophora and Spirogyra in laboratory experiments. Sterols can be quantified rapidly from a few milligrams of algae and appear to be a useful predictor of eukaryote biomass, whereas cellular levels of chl a vary substantially with light conditions. Phospholipids (or phospholipid fatty acids) are considered to be a reliable measure of viable microbial biomass. Nevertheless, phospholipid content varied substantially and unpredictably among algae and periphyton under different light regimes. Irradiance also had a significant effect on storage lipids: HL Cladophora and HL periphyton had 2 × and 5 × greater concentrations of triacylglycerols, respectively, compared to their LL forms. HL and LL algae also differed in the concentration of several major fatty acids. These light-induced changes in algal lipids and fatty acids have important implications for grazers.     

PHENOTYPIC CHARACTERIZATION AND HYDROGEN PRODUCTION IN CHLAMYDOMONAS REINHARDTII QB‐BINDING D1‐PROTEIN MUTANTS UNDER SULFUR STARVATION: CHANGES IN CHL FLUORESCENCE AND PIGMENT COMPOSITION1

The effects of Q_B‐binding D1‐protein mutations on the phenotypic characteristics and on hydrogen production of sulfur‐deprived Chlamydomonas reinhardtii P. A. Dang. cultures were investigated. The mutation involved one (D240) or double (D239–40) amino‐acid deletions at positions 240 and 239–240, respectively, in the loop connecting helices D and E of the D1 protein. Phenotypic characterization of the mutants showed the following peculiarities as compared to the wildtype (WT): (i) a higher sensitivity to photoinhibition, (ii) a reduced amount of chl per dry weight and per cell, (iii) a higher respiration‐to‐photosynthesis ratio, (iv) a higher carbohydrate accumulation during the aerobic phase, and (v) a higher synthesis of xanthophyll‐cycle pigments. These differences were translated into a 12‐ to 18‐fold higher hydrogen biogas production.     

INVOLVEMENT OF INDOLE‐3‐ACETIC ACID PRODUCED BY THE GROWTH‐PROMOTING BACTERIUM AZOSPIRILLUM SPP. IN PROMOTING GROWTH OF CHLORELLA VULGARIS1

Involvement of indole‐3‐acetic acid (IAA), produced by the microalgae‐growth‐promoting bacteria Azospirillum brasilens and A. lipoferum, in promoting growth of the microalga Chlorella vulgaris Beij. was studied. Four wildtype strains of Azospirillum and their IAA‐deficient mutants were co‐immobilized with C. vulgaris in alginate beads. Cultures were grown in synthetic growth medium supplemented with tryptophan. Growth promotion of microalgae and production of exogenous IAA by Azospirillum spp. were monitored. All wildtype Azospirillum spp. produced significant but varying amounts of IAA, while their mutant forms produced significantly less. The results demonstrated a significant growth promotion in Chlorella cultures when immobilized with the four wildtype strains of Azospirillum, while very low or no enhanced growth was induced by the four IAA‐deficient mutants, compared to when C. vulgaris is immobilized alone. A complementation experiment, where an IAA‐attenuated mutant (A. brasilense SpM7918) was supplemented with IAA produced by its parental wildtype strain (A. brasilense Sp6), restored growth promotion in the microalgae‐mutant culture.     

EFFECT OF NITROGEN STARVATION ON OPTICAL PROPERTIES,PIGMENTS, AND ARACHIDONIC ACID CONTENT OF THE UNICELLULAR GREEN ALGA PARIETOCHLORIS INCISA (TREBOUXIOPHYCEAE,CHLOROPHYTA)1

Spectral properties of cell suspensions, individual cells, and extracts of the unicellular green alga Parietochloris incisa (Reisigl) Shin Watan. grown under low light were studied. Long‐term nitrogen (N) deprivation resulted in a decrease of chloroplast volume, appearance of numerous large cytoplasmic oil bodies, and the deposition of triacylglycerols with a high proportion of arachidonic acid. Chlorophylls a and b underwent a synchronous decline, whereas carotenoids (Car) showed a relative increase. Simultaneously, significant qualitative changes in the spectral properties of P. incisa individual cells, cell extracts, and cell suspensions were observed. To a large extent, the spectral changes observed in cell suspension could be attributed to a decrease in overall pigment content, leading to a gradual weakening of the so‐called package effect and accumulation of additional amounts of Car over chl, most probably, in oil bodies. Several optical characteristics of cell suspensions could serve as sensitive indicators of N‐deficiency in P. incisa. Furthermore, the absorption ratios, A₄₇₆/A₆₇₆ and A₆₅₀/A_676, showed close correlations with the Car‐to‐chl ratio and relative arachidonic acid (AA) content, respectively. The latter makes it possible to suggest that the increase in AA percentage in P. incisa proceeds in parallel with a decrease in cell chl content, accounting for the weakening of the package effect. N‐replenishment resulted in complete recovery of cell optical properties. The possible significance of the changes in cell ultrastructure, pigments, lipids, and optical properties is discussed with special reference to the ability of algae to adapt to and survive under conditions of long‐term nutrient deficiency.     

DIEL CHANGES IN THE COMPOSITION OF PHOTOSYNTHETIC PIGMENTS AND CELLULAR CARBON AND NITROGEN IN CHATTONELLA ANTIQUA (RAPHIDOPHYCEAE)1

An axenic clonal culture of Chattonella antiqua (Hada) Ono was grown on a 12: 12 h LD cycle in a laboratory culture tank containing 1 m³ of f/2 medium. Diel changes in mean cell volume, cellular carbon (carbon content per cell), C/N ratio, cellular Chl a, Chl a/c ratio and carotenoid composition were observed. Mean cell volume and cellular C, N and pigments increased during the light period as a result of photosynthesis and decreased with increase of cell concentration by phased cell division during the dark period. These changes indicated that carbon assimilation and pigment synthesis occurred together during the light period. However, the patterns of increase were not the same since different diel patterns were also found in the ratios of C/N and chl a/c. Photosynthetic pigments were analyzed by reversed-phase high-performance liquid chromatography with ion-pairing solution. This analysis showed that the dominant carotenoids in C. antiqua were fucoxanthin, violaxanthin and β-carotene. Diel patterns of Chls a and c were similar to that of fucoxanthin but different from those of violaxanthin and β-carotene. The cellular contents of Chl a, fucoxanthin and carbon increased in a parallel manner during the light period. On the other hand, the increase of violaxanthin was restricted to only a few hours at the beginning of the light period during cell division cycles.     

EFFECT OF TEMPERATURE ON LIGHT-LIMITED GROWTH AND CHEMICAL COMPOSITION OF SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1

Phytoplankton growth rate in response to irradiance can be approximated by a hyperbola defined by three coefficients: i) initial slope (α); ii) asymptote (μ_m); and, iii) X-axis intercept or compensation irradiance (I_c). To mathematically represent the interaction of temperature and irradiance on growth rate, one must describe the relationship between these constants and temperature. The marine diatom, Skeletonema costatum (Greville) Cleve, was grown in unialgal culture at different levels of irradiance and 2-3 photoperiods at 0, 5, 10, 16 and 22 C. The value of I_c is ca. 1.0 ly·day^?1 or less at all temperatures. The initial slope (div·ly^?1) is a “u-shaped” function of temperature described by the second degree polynomial, α= 0.25–0.02T+0.001T². Within the range 0–10 C, μ_m (div·day^?1) is an exponential function of temperature described by the equation, μ_m= 0.48 exp (0.126T). At each temperature and selected levels of irradiance, cell size and cellular content of C, N and chl a were determined. The C:chl a and N:chl a ratios increased with irradiance because of increases in C and decreases in chl a. At lower temperatures (0, 5, 10 C), the rate of increase of both ratios with irradiance was greater than at the higher temperatures (16, 22 C). Cellular content of N was independent of irradiance and temperature, and the C:N ratio ranged from 5 to 8 with a slight tendency to lower values at low irradiance. Cell volume was not influenced by either temperature or irradiance.     

CHLOROPHYLL C PIGMENT PATTERNS IN 18 SPECIES (51 STRAINS) OF THE GENUS PSEUDO‐NITZSCHIA (BACILLARIOPHYCEAE)1

The pigment composition of 18 species (51 strains) of the pennate diatom Pseudo‐nitzschia was examined using HPLC. The carotenoid composition was typical for diatoms, with fucoxanthin (the major xanthophyll), diadinoxanthin, diatoxanthin, and β,β‐carotene. However, a diverse array of chl c pigments was observed in the studied strains. All Pseudo‐nitzschia strains contained chl a and chl c₂, traces of Mg‐2,4‐divinyl phaeoporphyrin a₅ monomethyl ester (MgDVP), and traces of a chl c₂–like pigment originally found in the haptophyte Pavlova gyrans. The distribution of chl c₁ and chl c₃ was variable among species (present in seven and 14 species, respectively). Based on chl c distribution, three major pigment types were defined: type 1 (chl c₁ + c₂, four species: P. australis, P. brasiliana, P. multiseries, and P. seriata), type 2 (chl c₁ + c₂ + c₃, three species: P. fraudulenta, P. multistriata, and P. pungens), and type 3 (chl c₂ + c₃, 11 species: P. arenysensis, P. calliantha, P. cuspidata, P. decipiens, P. delicatissima, P. galaxiae, P. mannii, P. pseudodelicatissima, P. subcurvata, P. cf. subpacifica, and a novel Pseudo‐nitzschia species). Type 1 and 2 species also shared the absence of a particular morphological character, the central nodule in the raphe, with the only exception of P. fraudulenta. The implications of such pigment diversity in chemotaxonomy, HAB monitoring, ecology, and phylogeny of Pseudo‐nitzschia species are discussed.