Behavioral responses of the coastal copepod Acartia hudsonica (Pinhey) to simulated dinoflagellate bioluminescence

Light pulses were used to mimic dinoflagellate bioluminescence and test its effects on the swimming behavior of Acartia hudsonica (Pinhey). The horizontal swimming patterns of the copepod were tracked and described using a video-computer system. Single flashes of light of 60 ms duration, with a wavelength of peak emission of 475 nm and an intensity of 2 μE · m^?2 · s^?1 caused a “startle” response consisting of a short burst of high speed swimming. A series of these flashes repeated every 5 s resulted in higher average swimming speed, more swimming speed bursts, and straighter paths. These behavioral changes are similar to those previously found for A. hudsonica in the presence of bioluminescent dinoflagellates. The effects of altering the intensity, duration, and color of the simulated dinoflagellate flash were also tested. Our results support the hypothesis that dinoflagellate bioluminescence is a highly evolved adaptation for repelling nocturnal grazers.     

SPONTANEOUS AND STIMULATED BIOLUMINESCENCE OF THE DINOFLAGELLATE CERATOCORYS HORRZDA (PERIDINIALES)1

This is the first report of spontaneous bioluminescence in the autotrophic dinoflagellate Ceratocorys horrida von Stein. Bioluminescence was measured, using an automated data acquisition system, in a strain of cultured cells isolated from the Sargasso Sea. Ceratocorys horrida is only the second dinoflagellate species to exhibit rhythmicity in the rate of spontaneous flashing, flash quantum flux (intensity), and level of spontaneous glowing. The rate of spontaneous flashing was maximal during hours 2–4 of the dark phase [i.e. circadian time (CT)16–18 for a 14:10 h LD cycle (LD14:10)], with approximately 2% of the population flashing-min^?1, a rate approximately one order of magnitude greater than that of the dinoflagellate Gonyaulax polyedra. Flash quantum flux was also maximal during this period. Spontaneous flashes were 134 ms in duration with a maximum flux (intensity) of 3.1×10⁹ quanta-s^?1. Light emission presumably originated from blue fluorescent microsources distributed in the cell periphery and not from the spines. Values of both spontaneous flash rate and maximum flux were independent of cell concentration. Isolated cells also produced spontaneous flashes. Spontaneous glowing was dim except for a peak of 6.4× 10⁴quanta-s^?1 cell^?1, which occurred at CT22.9 for LD14:10 and at CT22.8 for LD12:12. The total integrated emission of spontaneous flashing and glowing during the dark phase was 4×10⁹ quantacell^?1, equivalent to the total stimulable luminescence. The rhythms for C. horrida flash and glow behavior were similar to those of Gonyaulax polyedra, although flash rate and quantum flux were greater. Spontaneous bioluminescence in C. horrida may be a circadian rhythm because it persisted for at least three cycles in constant dark conditions. This is also the first detailed study of the stimulated bioluminescence of C. horrida, which also displayed a diurnal rhythm. Cultures exhibited >200 times more mechanically stimulated bioluminescence during the dark phase than during the light phase. Mechanical stimulation during the dark phase resulted in 6.7 flashes. cell^?1; flashes were brighter and longer in duration than spontaneous flashes. Cruise-collected cells exhibited variability in quantum flux with few differences in flash kinetics. The role of dinoflagellate spontaneous bioluminescence in the dynamics of near-surface oceanic communities is unknown, but it may be an important source of natural in situ bioluminescence.     

In situ measurements of bioluminescence response of Gonyaulax spinifera to various mechanical stimuli

A conspicuous bioluminescence during nighttime was reported in an aquaculture farm in the Cochin estuary due to Gonyaulax spinifera bloom on March 20, 2020. In situ measurements on bioluminescence was carried out during nighttime to quantify the response of G. spinifera to various mechanical stimuli. The bioluminescence intensity (BI) was measured using Glowtracka, an advanced single channel sensor, attached to a Conductivity–Temperature–Depth Profiler. In steady environment, without any external stimuli, the bioluminescence generated due to the movement of fishes and shrimps in the water column was not detected by the sensor. However, stimuli such as a hand splash, oar and swimming movements, and a mixer could generate measurable bioluminescence responses. An abundance of?~?2.7?×?10⁶ cells L^?1 of G. spinifera with exceptionally high chlorophyll a of 25 mg m^?3 was recorded. The BI in response to hand splash was recorded as high as 1.6?×?10¹¹ photons cm^?2 s^?1. Similarly, BI of?~?1–6?×?10¹⁰ photons cm^?2 s^?1 with a cumulative bioluminescence of?~?2.51?×?10¹² photons cm^?2 (for 35 s) was recorded when there is a mixer with a constant force of 494 N/800 rpm min^?1. The response of G. spinifera was spontaneous with no time lapse between application of stimuli and the bioluminescence response. Interestingly, in natural environment, application of stimulus for longer time periods (10 min) does not lower the bioluminescence intensity due to the replenishment of water thrusted in by the mixer from surrounding areas. We also demonstrated that the bioluminescence intensity decreases with increase in distance from the source of stimuli (mixer) (av. 1.84?×?10¹⁰ photons cm^?2 s^?1 at 0.2 m to av. 0.05?×?10¹⁰ photons cm^?2 s^?1 at 1 m). The BI was highest in the periphery of the turbulent wake generated by the stimuli (av. 3.1?×?10¹⁰ photons cm^?2 s^?1) compared to the center (av. 1.8?×?10¹⁰ photons cm^?2 s^?1). When the stimuli was applied vertically down, the BI decreased from 0.2 m (0.3?×?10¹⁰ photons cm^?2 s^?1) to 0.5 m (0.10?×?10¹⁰ photons cm^?2 s^?1). Our study demonstrates that the BI of G. spinifera increases with increase in mechanical stimuli and decreases with increase in distance from the stimuli.

     

PLANKTONIC SARCODINES: MICROHABITAT FOR OCEANIC DINOFLAGELLATES1

Two morphologically distinct species of free-swimming dinoflagellates belonging to the genus Gyrodinium utilize the spine and rhizopodial environments of planktonic foraminifera and colonial radiolaria as microhabitats. Up to 84% of the sarcodines examined in a given population were associated with these dinoflagellates at densities up to 20,000 cells per sarcodine in some radiolarian colonies. Both dinoflagellate species possess chloroplasts, indicating they are capable of autotrophy. ¹⁴C-labelling experiments with the radiolarian-associated dinoflagellate demonstrate that it can take up inorganic carbon under both light and dark conditions. Ultrastructural evidence suggests the foraminiferal dinoflagellate may be capable of phagotrophy. Hence, these algae should be considered mixotrophs. An unusual cytoplasmic extension used for attachment and possibly feeding occurs in the foraminiferal-associated Gyrodinium and is documented with electron microscopy. Ultrastructural examination suggests this organelle may be hydrostatically controlled and may be an extension of the sac pusule.     

Bioluminescence of Marine Dinoflagellates : I. An underwater photometer for day and night measurements

Portable light-baffled underwater photometers have been designed for the measurement of dinoflagellate bioluminescence by day and night. Maximal light emission is obtained by mechanical stimulation in a defined volume. The pump which stimulates the dinoflagellates also constantly replenishes the sample volume so that continuous measurements are possible. Evidence for both diurnal variation and vertical migration is presented. Using luminous bacteria for calibration a single dinoflagellate has been found to emit of the order of 10¹⁰ light quanta per flash. The technique suggests that large scale mapping of bioluminescence is feasible.     

Trapping and annihilation in the antenna system of Photosystem I

The primary charge separation in Photosystem I of pea chloroplasts was measured as a photovoltage in the pico- and nanosecond time range by applying laser flashes at 532 nm of variable energy and different duration (12 ns and 30 ps, respectively). Contributions to the photovoltage from Photosystem II was eliminated by addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and preillumination. The dependence of the photovoltage amplitude on the excitation energy could be described by an exponential saturation law when the excitation flash had a duration of 12 ns. Nearly the same dependence was found when the excitation source was the train of a mode-locked laser (approx. ten 30-ps flashes spaced by 7 ns; highest energy of a single flash, 80 μJ / cm⁻²). Even with single 30-ps flashes the photovoltage was only slightly smaller than the one elicited by 12-ns flashes of the same energy. These findings demonstrate that trapping of excitation energy by the reaction center of Photosystem I is much more effective than losses by annihilation and other loss processes. The photovoltage yield was nearly independent of the fraction of closed traps, thus demonstrating that the absorption cross section of Photosystem I is not altered by the closing of its reaction centers. By recording the rise time of the photovoltage with our highest time resolution we found that the trapping rate of the excitation energy in Photosystem I depended on the energy of the 30-ps flashes: at low excitation energies (less than 10¹⁴ photons / cm² per pulse) trapping occurred within 90 ± 15 ps and at high excitation energy (10¹⁵ photons / cm² per pulse) trapping and charge stabilization occurred within the time resolution of the apparatus, i.e., up to 50 ps. The trapping rate at low energies is in agreement with the one determined by fluorescence decay kinetics. Up to 50 ns there was no further detectable electrogenic phase (neither forward nor backward reactions). This demonstrates that all the electrogenicity, produced by the charge separation, takes place in less than 50 ps.     

SPECIES OF OCEANIC DINOFLAGELLATES IN THE GENERA DISSODINIUM AND PYROCYSTIS: INTERCLONAL AND INTERSPECIFIC COMPARISONS OF THE COLOR AND PHOTON YIELD OF BIOLUMINESCENCE1

We have examined aspects of the bioluminescence of 5 clones of Dissodinium, 1 clone of Pyrocystis acuta, 4 clones of Pyrocystis fusiformis, and 5 clones of Pyrocystis noctiluca. All clones produced the same color bioluminescence with an intensity peak near 474 nm. The in vivo emission spectra of these clones agreed with those previously determined, for 4 other species of marine dinoflagellates. The amount of light emitted by the dinoflagellates in scotophase when mechanically stimulated to exhaustion was determined for most of the clones. The largest species, P. noctiluca and P. fusiformis, emitted 37–89 × 10⁹ photons cell^?1 and 23–62 × 10⁹ photons cell^?1, respectively, about a thousand, times as much light as Gonyaulax species. Pyrocystis acuta emitted 3–6 × 10⁹ photons cell^?1. Three of the 5 clones of Dissodinium were bioluminescent. The range for 3 clones was 5–13 × 10⁹ photons cell^?1. All 5 clones of Dissodinium are morphologically distinct. Both the clones of Dissodinium and Pyrocystis produced much higher numbers of photons per cell nitrogen (ca. 7–50 times) than Gonyaulax polyedra or Pyrodinium bahamense. The data suggested that enzyme turnover occurred in the reactions producing light during mechanical stimulation of Dissodinium and Pyrocystis species.     

ALKALINE PHOSPHATASE ACTIVITIES AMONG POPULATIONS OF THE COLONY-FORMING DIAZOTROPHIC CYANOBACTERIUM TRICHODESMIUM SPP. (CYANOBACTERIA) IN THE RED SEA

Alkaline phosphatase activities of the diazotrophic marine cyanobacterium Trichodesmium were studied among natural populations in the northern Red Sea and in laboratory cultures of Trichodesmium sp. strain WH9601. Open-water tuft-shaped colonies of Trichodesmium showed high alkaline phosphatase activities with 2.4–11.7 μmol p-nitrophenylphosphate (PNPP) hydrolyzed·μg chl a ^{− 1}·h ^{− 1}, irrespective of date or origin of the sample. Coastal populations of the Trichodesmium tuft colonies had low alkaline phosphatase activities with 0.2–0.5 μmol PNPP·μg chl a ^{− 1}·h ^{− 1}. An exception was the Trichodesmium fall maximum, when both tuft colonies and the plankton community (<100 μm) had alkaline phosphatase activities of 0.6–7.4 μmol PNPP·μg chl a ^{− 1}·h ^{− 1}. Likewise, the more rare puff and bow-tie colonies of Trichodesmium spp. in coastal waters had elevated alkaline phosphatase activities (0.8–1.6 μmol PNPP·μg chl a ^{− 1}·h ^{− 1}) as compared with tuft colonies coinhabiting the same waters. Intact filaments of tuft-forming Trichodesmium sp. strain WH9601 from phosphate-replete cultures had a base alkaline phosphatase activity of 0.5 μmol PNPP·μg chl a ^{− 1}·h ^{− 1}. This activity underwent a 10-fold increase in phosphate-deplete cultures and in cultures supplied with glycerophosphate as the sole P source. The elevated level of alkaline phosphatase activity was sustained in P-deplete cultures, but it declined in cultures with glycerophosphate. The decline is suggested to result from feedback repression of alkaline phosphatase synthesis by the phosphate generated in the glycerophosphate hydrolysis. The enhanced alkaline phosphatase activities of Trichodesmium spp. populations provide evidence that P stress is an important factor in the ecology of Trichodesmium in the northern Red Sea.     

Interannual dynamics of putative parasites (Syndiniales Group II) in a coastal ecosystem

Temporal dynamics of Syndiniales Group II were investigated combining 18S rDNA amplicon sequencing and direct microscopy counts (fluorescence in situ hybridization-tyramide signal amplification [FISH-TSA]) during 5 years. The study was undertaken in meso-eutrophic coastal ecosystem, dominated by diatoms, the haptophyte Phaeocystis globosa and exhibiting relatively low dinoflagellate abundance (max. 18.6 × 10³ cells L⁻¹). Consistent temporal patterns of Syndiniales Group II were observed over consecutive years highlighting the existence of local populations. According to sequencing data, Syndiniales Group II showed increasing abundance and richness in summer and autumn. Dinospores counted by microscopy, were present at low abundances and were punctuated by transient peaks. In summer dinospore highest abundance (559 × 10³ L⁻¹) and prevalence (38.5%) coincided with the peak abundance of the dinoflagellate Prorocentrum minimum (13 × 10³ L⁻¹) while in autumn Syndiniales Group II likely had more diversified hosts. Although, several peaks of dinospore and read abundances coincided, there was no consistent relation between them. Ecological assembly processes at a seasonal scale revealed that stochastic processes were the main drivers (80%) of the Group II community assembly, though deterministic processes were noticeable (20%) in June and July. This latter observation may reflect the specific Syndiniales—dinoflagellate interactions in summer.     

Kinetics of picosecond bacteriochlorophyll luminescence in vivo as a function of the reaction center state

Bacteriochlorophyll (BChl) luminescence lifetimes (τ) were measured in purple bacteria Rhodospirillum rubrum and Rhodopseudomonas sphaeroides at low-excitation pulse energy with the use of a picosecond luminescence spectrochronograph of high sensitivity and high time-resolution. Average high-frequency excitation light density was changed from about 1 · 10¹³ photons · cm⁻² · s⁻¹ up to 1 · 10¹⁷ photons · cm⁻². s⁻¹. Maximal energy density in a single pulse was in the range 10⁻¹⁴–10⁻¹⁰ J/cm², which completely rules out nonlinear exciton interactions. In this range τ increased as a function of excitation light density from about 60 ps to 210 ps. Luminescence yield (ø) for the bacteria investigated measured under continuous or picosecond excitation changed in a similar manner as τ. The luminescence increase was shown to accompany the conversion of the reaction centers to the closed, photooxidized state. Luminescence decay of R. rubrum and Rps. sphaeroides chromatophores without any chemical additions was well approximated by a single exponential component both at low and at saturating intensities of exciting light. The time necessary for the primary charge separation to occur was shown to be 60 ± 10 ps. The pairwise jump-time of excitation-energy transfer, as well as excitation-diffusion characteristics were estimated from these data. On the basis of life-time measurements in the state of active photosynthesis, the quantum yield of the primary charge separation in the reaction centers was estimated to be equal to 0.95 ± 0.02. In intact cells as well as in chromatophores in the presence of reducing agents, a nanosecond component of emission decay was also observed. The relative amplitude of this component, being several percent of the picosecond one at low-excitation intensity levels, increased (2–3)-times with excitation density. Its life-time was estimated to be 3 ± 1 ns. The nanosecond component appeared only under conditions when a part of the reaction centers were converted to the closed state PQ⁻.     

Gas exchange characteristics of Gulf of Mexico coastal marsh macrophytes

Gas exchange characteristics of three major Louisiana Mississippi River deltaic plain marsh species, Spartina patens (Ait.) Muhl., Spartina altemiflora Lois., and Panicum hemitomon Shult., was studied under controlled environment conditions. The optimum temperature for maximum photosynthesis was ≈ 36 °C for S. patens, 27 °C for S. alterniflora, and 28 °C for rP. hemitomon. Net photosynthesis rates at optimum temperature averaged 20.1 μmol · m^t-2 · s^t-1 in S. patens, 22.8 μmol · m⁻² · s⁻¹ in S. alterniflora, and 11.4 μmol · m⁻² · s⁻¹ in P. hemitomon. Photosynthetic light saturation occurred ≈720, 530, and 750 μmol · m⁻² · s⁻¹ in S. patens, S. alterniflora, and P. hemitomon, respectively. Only S. patens had a midday depression of stomatal conductance, but net photosynthesis was not reduced by the depression. Maximum stomatal conductances were 285 mmol · m⁻² · s⁻¹ in S. patens, 238 mmol · m⁻² · s⁻¹ in S. alterniflora, and 335 mmol · m⁻² · s⁻¹ in P. hemitomon. In contract, net photosynthesis values were lower in P. hemitomon compared with the Spartina species, indicating a greater degree of water use efficiency of photosynthesis for both Spartina species.     

Partitioning of oxygen consumption between “maintenance” and “growth” in developing herring Clupea harengus (L.) embryos

Growth and oxygen consumption was measured in developing herring Clupea harengus (L.) embryos. By considering the variations in oxygen consumption with embryonic size and growth rate, an attempt was made to partition oxygen consumption between growth related and growth unrelated (i.e., “maintenance”) processes. The metabolic cost of growth was estimated as ≈ 150 ng O₂ · μg dry wt tissue formed⁻¹. This estimate compares favourably with the biochemical estimate of the costs of transport and net biosynthesis. The “maintenance” component was proportional to embryonic mass (77 ng O₂ · μg⁻¹· d⁻¹). Over the entire embryonic period, growth processes were responsible for ≈ 25% of the cumulated oxygen consumption.     

CULTURE OF THE TERRESTRIAL CYANOBACTERIUM,NOSTOC FLAGELLIFORME (CYANOPHYCEAE), UNDER AQUATIC CONDITIONS1

Both colonies and free‐living cells of the terrestrial cyanobacterium, Nostoc flagelliforme (Berk. & Curtis) Bornet & Flahault, were cultured under aquatic conditions to develop the techniques for the cultivation and restoration of this endangered resource. The colonial filaments disintegrated with their sheaths ruptured in about 2 days without any desiccating treatments. Periodic desiccation played an important role in preventing the alga from decomposing, with greater delays to sheath rupture with a higher frequency of exposure to air. The bacterial numbers in the culture treated with seven periods of desiccation per day were about 50% less compared with the cultures without the desiccation treatment. When bacteria in the culture were controlled, the colonial filaments did not disintegrate and maintained the integrity of their sheath for about 20 days even without the desiccation treatments, indicating the importance of desiccation for N. flagelliforme to prevent them from being disintegrated by bacteria. On the other hand, when free‐living cells obtained from crushed colonial filaments were cultured in liquid medium, they developed into single filaments with sheaths, within which multiple filaments were formed later on as a colony. Such colonial filaments were developed at 15, 25, and 30° C at either 20 or 60 μmol photons·m^?2·s^?1; colonies did not develop at 180 μmol photons·m^?2·s^?1, though this light level resulted in the most rapid growth of the cells. Conditions of 60 μmol photons·m^?2·s^?1 and 25° C appeared to result in the best colonial development and faster growth of the sheath‐held colonies of N. flagelliforme when cultured indoor under aquatic conditions.     

THE ROLE OF CALCIUM IN FLOW‐STIMULATED BIOLUMINESCENCE OF THE RED TIDE DINOFLAGELLATE LINGULODINIUM POLYEDRUM

Many marine planktonic dinoflagellates emit flashes of light in response to either laminar or turbulent flows as well as direct mechanical stimulation. The production of a flash of light is known to be mediated by a proton‐mediated action potential across the vacuolar membrane; the mechanotransduction process initiating this action potential is unknown. Here we report on an investigation into the role of Ca⁺² in the mechanotransduction process regulating bioluminescence in the red tide dinoflagellate Lingulodinium polyedrum. Calcium ionophores and low concentrations of the membrane‐disrupting agent digitonin stimulated bioluminescence only when calcium was present in the media or added with the agent, indicating that the flash‐triggering vacuolar action potential is specifically stimulated by a calcium influx. A variety of known calcium channel blockers or antagonists inhibited mechanically stimulated bioluminescence but did not affect cellular bioluminescent capacity. In many cases the inhibitory affect occurred after only a brief exposure. In addition, gadolinium (Gd⁺³), a blocker of many stretch‐activated ion channels, caused potent inhibition of mechanically stimulated bioluminescence. The order of potency of the transition metals tested was La⁺³ > Gd⁺³ > Co⁺² > Mn⁺² > Ni⁺², similar to their potency as blockers of known calcium channels. Experiments with a quantified shear flow demonstrated that flow‐stimulated bioluminescence depended on the level of extracellular calcium. Future work will elucidate the signaling pathway involving calcium‐mediated flow‐stimulated mechanotransduction. Our goal is to use bioluminescence as a proxy for the initial cellular mechanotransduction events triggered by fluid flow.     

Transition kinetics of the conversion of blue to purple bacteriorhodopsin upon magnesium binding

Magnesium binding to cation-depleted blue bacteriorhodopsin (b-bR) was studied spectrophotometrically as well as by following stopped-flow kinetics. There exist three kinetically different steps in the binding process, yielding purple bacteriorhodopsin (p-bR). Since only the firtst step is dependent on the concentration of the reactants, the reaction scheme

can be proposed as the simplest model, with MgbR being the first intermediate and ΣI denoting a set of successive intermediates. According to this model k₁, k₋₁ and k₂ are calculated to be 2.8 × 10⁴ M⁻¹ · s⁻¹, 5.0 × 10 s⁻¹ and 1 × 10⁻² s⁻¹, respectively.     

Formation and decay of radical-pair state P+I− in Chloroflexus aurantiacus reaction centers

We have examined the room temperature kinetics of the absorption changes associated with the formation of state P⁺I⁻ (P⁺BPh⁻) and its subsequent decay to state P⁺Q⁻_A in reaction centers from Chloroflexus aurantiacus. Our data, acquired using 30-ps excitation flashes, strongly suggest that formation of P⁺I⁻ (P⁺BPh⁻) takes longer in Chloroflexus than in reaction centers from Rhodopseudomonas sphaeroides. The reduction of the photoactive bacteriopheophytin (BPh) could take as long as 13 ps. Absorption changes different from those due to P⁺I⁻ are observed early in the excitation flash, but the detailed identity of the transient remains unclear. We also find that the kinetics observed subsequent to P⁺I⁻ formation differ with detection wavelength. The time constant measured in the anion band (I⁻) at 655 nm is 324 ± 20 ps and probably reflects the rate of electron transfer from I⁻ (BPh⁻) to Q_A. However, the kinetics measured in the BPh ground-state absorption bands are slightly longer: 365 ± 19 and 367 ± 21 ps at 538 and 760 nm, respectively. At 810 nm, a wavelength normally associated with the monomeric bacteriochlorophyll (BChl) in the Chloroflexus reaction center, a slightly faster (281 ± 19 ps) time constant is observed. This detection-wavelength dependence of the kinetics is similar to that observed recently in Rps. sphaeroides reaction centers. Comparison of these results suggests that the kinetics observed in the ground-state absorption bands of the BPhs and BChls in Chloroflexus may contain contributions from readjustments of the pigments and/or protein in response to the charge separation process.     

Influence of planting geometry on photosynthetically active radiation interception and dry matter production relationships in pearl millet

A field experiment was conducted at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Center, Patancheru, India to study photosynthetically active radiation (PAR) interception and dry matter production relationships in pearl millet (Pennisetum americanum (L.) Leeke). Two pearl millet genotypes, BJ 104 (G₁) and ICH 226 (G₂) were sown at three planting geometries obtained by using combinations of row and plant spacings (S₁: 37·5 cm × 26·6 cm; S₂: 75·0 cm × 13·3 cm; S₃: 150·0 cm × 6·6 cm) such that plant population was constant at 100 000 ha⁻¹ in all treatments. Cumulative intercepted PAR was maximum (330 MJ m⁻²) in G₂S₂ and minimum (268 MJ m⁻²) in G₁S₃. Conversion efficiency values ranged from 1·87 g MJ⁻¹ in G₁S₂ to 2·32 g MJ⁻¹ in G₂S₃. Final above-ground dry matter followed the pattern of cumulative intercepted PAR and maximum dry matter (7·22 Mg ha⁻¹) was produced by G₂S₂ while G₁S₃ produced minimum dry matter (4·97 Mg ha⁻¹).     

Pharmacological investigation of the bioluminescence signaling pathway of the dinoflagellate Lingulodinium polyedrum: evidence for the role of stretch‐activated ion channels

Dinoflagellate bioluminescence serves as a whole‐cell reporter of mechanical stress, which activates a signaling pathway that appears to involve the opening of voltage‐sensitive ion channels and release of calcium from intracellular stores. However, little else is known about the initial signaling events that facilitate the transduction of mechanical stimuli. In the present study using the red tide dinoflagellate Lingulodinium polyedrum (Stein) Dodge, two forms of dinoflagellate bioluminescence, mechanically stimulated and spontaneous flashes, were used as reporter systems to pharmacological treatments that targeted various predicted signaling events at the plasma membrane level of the signaling pathway. Pretreatment with 200 μM Gadolinium III (Gd³⁺), a nonspecific blocker of stretch‐activated and some voltage‐gated ion channels, resulted in strong inhibition of both forms of bioluminescence. Pretreatment with 50 μM nifedipine, an inhibitor of L‐type voltage‐gated Ca²⁺ channels that inhibits mechanically stimulated bioluminescence, did not inhibit spontaneous bioluminescence. Treatment with 1 mM benzyl alcohol, a membrane fluidizer, was very effective in stimulating bioluminescence. Benzyl alcohol‐stimulated bioluminescence was inhibited by Gd³⁺ but not by nifedipine, suggesting that its role is through stretch activation via a change in plasma membrane fluidity. These results are consistent with the presence of stretch‐activated and voltage‐gated ion channels in the bioluminescence mechanotransduction signaling pathway, with spontaneous flashing associated with a stretch‐activated component at the plasma membrane.     

PHOTOINHIBITION OF MECHANICALLY STIMULABLE BIOLUMINESCENCE IN THE HETEROTROPHIC DINOFLAGELLATE PROTOPERIDINIUM DEPRESSUM (PYRROPHYTA)1

Photoinhibition of mechanically stimulable bioluminescence (MSL) in the heterotrophic dinoflagellate Protoperidinium depressum Bailey was investigated using samples collected from the Massachusetts and southern Texas coasts. The times for both photoinhibition of MSL (ca. 10 min) and dark recovery from photoinhibition of MSL (ca. 45 min) in this species were similar to those reported for autotrophic dinoflagellates. The degree of photoinhibition of MSL was a linear function of the logarithm of photon flux density (PFD). The threshold PFDs for the photoinhibition of MSL were 0.02, 0.6, and 21 μmol photons · m^?2· s^?1 for broad-band blue, green, and red light, respectively. These PFDs are lower than those required for photoinhibition of MSL by the autotrophic dinoflagellates Pyrocystis lunula and Ceratium fusus. We speculate that photosynthetic pigments in autotrophic dinoflagellates shield the photoreceptor that causes photoinhibition of MSL, thus lowering the sensitivity of these dinoflagellates to light. When field-collected P. depressum were kept in the laboratory without growth for a week, photoinhibition of MSL's sensitivity to light increased progressively along with 1) a decrease in its bioluminescence capacity (BCAP), 2) a decrease in the ratio of MSL to BCAP (MSL/BCAP), and 3) a decrease in the orange pigmentation (probably carotenoid) of the dinoflagellate. The action spectrum for photoinhibition of MSL in P. depressum was characterized primarily with a broad peak in the blue extending into the green. We suggest that carotenoid was not a photoreceptor for the photoinhibition of MSL in P. depressum because the peak of the action spectrum was too broad and extended too far into the green part of the spectrum, and because the orange pigment present decreased as photoinhibition of MSL became more sensitive to light.     

Weak Electron–Phonon Coupling and Enhanced Thermoelectric Performance in n-type PbTe–Cu2Se via Dynamic Phase Conversion

This study investigates Ga-doped n-type PbTe thermoelectric materials and the dynamic phase conversion process of the second phases via Cu₂Se alloying. Introducing Cu₂Se enhances its electrical transport properties while reducing its lattice thermal conductivity (κ_lat) via weak electron–phonon coupling. Cu₂Te and CuGa(Te/Se)₂ (tetragonal phase) nanocrystals precipitate during the alloying process, resulting in Te vacancies and interstitial Cu in the PbTe matrix. At room temperature, Te vacancies and interstitial Cu atoms serve as n-type dopants, increasing the carrier concentration and electrical conductivity from ≈1.18 × 10¹⁹ cm⁻³ and ≈1870 S cm⁻¹ to ≈2.26 × 10¹⁹ cm⁻³ and ≈3029 S cm⁻¹, respectively. With increasing temperature, the sample exhibits a dynamic change in Cu₂Te content and the generation of a new phase of CuGa(Te/Se)₂ (cubic phase), strengthening the phonon scattering and obtaining an ultralow κ_lat. Pb_0.975Ga_0.025Te-3%CuSe exhibits a maximum figure of merit of ≈1.63 at 823 K, making it promising for intermediate-temperature device applications.