Biomedical subjects

P Juneau

Publications and source records attributed to P Juneau.

At least 19 recordsLinked to original sources

PubMed2003

Validation of a flow cytometric acridine orange micronuclei methodology in rats.

Our laboratory has previously reported a flow cytometric acridine orange method for detection of micronucleus (MN) in the rat using cyclophosphamide as a test compound. To replace the manual method of scoring and satisfy Good Laboratory Practice (GLP) requirements, an extensive validation of the flow method was required. Therefore, manual scoring and flow cytometric determination of MN were compared using vincristine, chlorambucil, methotrexate, and doxorubicin compounds known to induce MN formation with various mechanisms of action. 1,2-Dimethylhydrazine (1,2-DH), a compound with negative or equivocal MN findings also was evaluated. The flow method consistently demonstrated dose- and time-dependent responses for MN production at all concentrations of vincristine, methotrexate, clorambucil, and doxorubicin. In contrast, manual scoring of slides failed to detect an increase in MN at the lowest doses of doxorubicin (1mg/kg) at 24 or 48 h, and methotrexate at 48 h, or any dose of methotrexate (50, 100, or 250 mg/kg) at 24h. Additionally, a dose-response for methotrexate at 48 h, and chlorambucil at 24 h were missed using manual scoring. For 1,2-DH, the flow method showed a low level (< 1.4-fold) increase in MN at all doses and times. In contrast, the manual method showed five-seven-fold increases at 24 h, but a < two-fold increase at 48 h in the highest dose only. These data may suggest that the flow method has a greater sensitivity and possibly accuracy than manual scoring. Significant decreases in polychromatic erythrocytes (PCE) were seen using both methods at approximately the same dose for all compounds. However, absolute flow cytometric PCE values were consistently higher than manual. Additional cytotoxicity parameters obtained by the flow method allowed a more complete assessment of cytotoxicity than PCE alone. Furthermore, data reported here combined with improved throughput, shortened data turnaround and reporting times, and possibly better precision due to evaluation of much larger numbers of cells clearly demonstrate the usefulness of flow cytometry method in the routine micronucleus evaluation.

1,2-Dimethylhydrazine↗

PubMed2002

PAM fluorometry in the determination of the sensitivity of Chlorella vulgaris, Selenastrum capricornutum, and Chlamydomonas reinhardtii to copper.

The pulse-amplitude-modulation (PAM) fluorometric method was used in the past as a sensitive and rapid method for assessing toxic effect of pollutants in plants. Here, we used the advantages of this method to evaluate the difference in sensitivity of Chlorella vulgaris, Selenastrum capricornutum, and Chlamydomonas reinhardtii to copper toxicity. We found by using the PAM-fluorescence parameters (phiM, phi'M, QP, and QN), that C. reinhardtii is the most sensitive species, followed by S. capricornutum and C. vulgaris. Indeed, the copper 5-, 48-, and 96-h EC50 for phiM, phi'M, and QP vary between 11 and 34 microg/L for C. reinhardtii, while for S. capricornutum this value is between 25 and 50 microg/L. However, the same parameters obtained from C. vulgaris did not show susceptibility to copper, even at very high concentrations (100 microg/L). In this study, the estimated 5-h EC50 for C. reinhardtii and S. capricornutum are lower than the 24-h EC50 reported earlier for these species with other bioassays, indicating that the use of PAM fluorometry in copper bioassay provides a more sensitive method than the other biotests in aquatic toxicology.

Biological Assay↗

PubMed2001

Evaluation of different algal species sensitivity to mercury and metolachlor by PAM-fluorometry.

In this study, the pulse-amplitude-modulation (PAM)-fluorometric method was used to evaluate the difference in the sensitivity to mercury (Hg) and metolachlor of six algal species: Ankistrodesmus falcatus, Selenastrum capricornutum, Chlorella vulgaris, Nannoplankton (PLS), Microcystis aeruginosa and Pediastrum biwae. We found that the fluorescence parameters (phiM, the maximal photosystem II (PSII) quantum yield, phi'M, the operational PSII quantum yield at steady state of electron transport, Q(P), the photochemical quenching value, and Q(N), the non-photochemical quenching value) were appropriate indicators for inhibitory effects of mercury but only phi'M and Q(N) were useful for metolachlor. The examined algal species showed very different levels of sensitivity to the effect of Hg and of metolachlor. The most sensitive species to Hg and metolachlor were respectively M. aeruginosa and A. falcatus, while the least sensitive were C. vulgaris and P. biwae. We interpreted these differences by the action mode of pollutants and by the different metabolism properties and morphological characteristics between algal species. These results related to fluorescence parameters may offer useful tool to be used in bioassay for different pollutants. Heterogeneous algal sensitivity to the same pollutant suggests the need to use a battery of species to evaluate the effects of mixtures of pollutants in aquatic systems.

Acetamides↗

PubMed2001

Repeated analysis of semen parameters in beagle dogs during a 2-year study with the HMG-CoA reductase inhibitor, atorvastatin.

Sperm analyses are often incorporated into reproductive toxicity studies in rats. Due to the relative ease of collecting multiple samples throughout a study, semen analysis in non-rodents such as dogs offers the opportunity to assess potential development of functional effects of compounds on male reproduction over time. In the present study, semen parameters were evaluated in beagle dogs during and at termination of a chronic toxicity study with the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, atorvastatin. Male dogs received 0, 10, 40, or 120 mg/kg orally in gelatin capsules for up to 104 weeks (n = 10/group). After 52 weeks of dosing, 3 dogs/group were euthanized, and 2/group were withdrawn from treatment for a 12-week reversal period and euthanized at Week 64. The remaining 5/group continued treatment until Week 104. Semen was collected from all animals for 3 consecutive weeks prior to termination of the 52-week animals (Weeks 50, 51, 52) for analysis of sperm parameters, using manual methods of evaluation. Semen was collected from the remaining animals at Weeks 64, 78, 91, and 104, and was analyzed. At necropsy, testes, epididymides, and prostates were weighed and evaluated histologically, and epididymal sperm counts were determined. Serum cholesterol was decreased 25--60% at all doses during the study. There were no drug-related differences in semen volume and color, total sperm count, and sperm concentration, morphology, progressiveness, and percent motility during treatment with atorvastatin. There were also no effects on reproductive organ weights or histopathology, and no effects on epididymal sperm count. Thus, incorporation of semen analyses into this study allowed the evaluation of potential male reproductive effects in dogs at multiple time points during the study. Statistical power calculations demonstrated acceptable statistical power (> 80%) for semen sperm count, concentration, morphology, and motility with group sizes of 8--10 animals, and for semen sperm count and concentration or epididymal sperm count with group sizes of 3--5 animals, using the methodology described in this paper.

Acyl Coenzyme A↗

PubMed2001

Spectroscopic analysis of desiccation-induced alterations of the chlorophyllide transformation pathway in etiolated barley leaves.

Effects of water deficit on the chlorophyllide (Chlide) transformation pathway were studied in etiolated barley (Hordeum vulgare) leaves by analyzing absorption spectra and 77-K fluorescence spectra deconvoluted in components. Chlide transformations were examined in dehydrated leaves exposed to a 35-ms saturating flash triggering protochlorophyllide (Pchlide) and Chlide transformation processes. During the 90 min following the flash, we found that dehydration induced modifications of Chlide transformations, but no effect on Pchlide phototransformation into Chlide was observed. During this time, content of NADPH-Pchlide oxydoreductase in leaves did not change. Chlide transformation process in dehydrated leaves was characterized by the alteration of the Shibata shift process, by the appearance of a new Chlide species emitting at 692 nm, and by the favored formation of Chl(ide) A(668)F(676). The formation of Chl(ide) A(668)F(676), so-called "free Chlide," was probably induced by disaggregation of highly aggregated Chlide complexes. Here, we offer evidence for the alteration of photoactive Pchlide regeneration process, which may be caused by the desiccation-induced inhibition of Pchlide synthesis.

Adaptation, Physiological↗

PubMed2000

The antithrombotic effects of CI-1028, an orally bioavailable direct thrombin inhibitor, in a canine model of venous and arterial thrombosis.

Direct thrombin inhibitors represent a new class of drug that may offer a therapeutic alternative for the treatment and prevention of thrombembolic conditions, especially on the venous side of the systemic circulation. CI-1028 (PD 172524/LB30057) is a potent, highly selective inhibitor of thrombin that is orally bioavailable. The efficacy of this compound has been demonstrated in animal models in which intra-venous administration was used. The objective of this study was to evaluate the efficacy of CI-1028 after oral administration in a canine electrolytic injury model of venous and arterial thrombosis. CI-1028 was administered via oral gavage, and animals received either saline or 10, 15, 20, or 30 mg/kg of drug. Fifteen minutes later, the dogs were anesthetized and a femoral artery and vein were exposed and instrumented to induce electrolytic injury and thrombosis while continuously monitoring blood flow in the vessels. Maximum blood CI-1028 concentrations of 0.88+/-0.27, 1.8+/-0.3, 2.2+/-0.5, and 3.2+/-0.5 microg/mL were generally achieved 15 to 30 minutes after administering the compound in the 10-, 15-, 20-, and 30-mg/kg groups, respectively. Administration of CI-1028 increased the time to occlusion (TTO), the principal efficacy end point, in a dose-dependent manner in both arteries and veins. The TTO in the control group (n=8) averaged 66+/-11 minutes in the arteries and 69+/-6 minutes in the veins. In dogs treated with 10 mg/kg (n=8), the TTO was not significantly different from that of the control group. In the 15-mg/kg group (n=9) TTO averaged 140+/-27 minutes in the arteries (p=not significant) and 125+/-15 minutes (p<0.05) in the veins. In the 20-mg/kg group (n=8), TTO was significantly longer than controls in both types of vessels, averaging 168+/-30 minutes in the arteries (p=0.05) and 155+/-21 minutes (p<0.05) in the veins. Likewise, at 30 mg/kg (n=8) both the arterial (179+/-17 minutes) and venous (188+/-15 minutes) TTO was significantly prolonged compared with controls. Surgical blood loss and template bleeding times tended to increase in a dose-dependent manner but a statistically significant elevation was detected for template bleeding time only at the highest dose. Dramatic changes in thrombin time were detected, consistent with the CI-1028 mechanism of action. Virtually no changes were detected in prothrombin time. Maximum activated partial thromboplastin time (aPTT) and activated clotting time changes were detected approximately 30 minutes after dosing, and they were approximately twofold and fivefold baseline values, respectively, at the highest dose. In conclusion, these results demonstrate that CI-1028 provides dose-dependent antithrombotic efficacy after oral administration in a canine model of venous and arterial thrombosis.

Administration, Oral↗

PubMed2000

Evidence of chlorophyll synthesis pathway alteration in desiccated barley leaves.

In etiolated leaves, saturating flash of 200 ms induces phototransformation of protochlorophyllide (Pchlide) F655 into chlorophyllide (Chlide), then into Chl through reactions which do not need light sensibilisation. The synthesis of Chl is known to be slowed down in etiolated leaves exposed to desiccation stress. In order to analyse the intensity and time-course of Chlide transformation into Chl, we used the fluorescence emission of etiolated leaves previously exposed to a 200 ms saturating flash. We used low-temperature fluorescence spectroscopy to reveal the inhibition site of Chl synthesis in etiolated barley leaves exposed to water stress. Shibata shift appears as the main target point of the water deficit. It was found that water deficit inhibits partially active Pchlide F655 regeneration. Also, esterification of Chlide into Chl is impaired. It appears that these inhibitory effects alter the appearance of PSII active reaction centres.

Chlorophyll↗

PubMed2000

Analysis of a mutation in phosphodiesterase type 4 that alters both inhibitor activity and nucleotide selectivity.

Cyclic nucleotide phosphodiesterase type 4 (PDE4) is a cAMP-specific phosphodiesterase that is found as four distinct genes in the mammalian genome (PDE4A, 4B, 4C, and 4D). Mutation analysis was done to identify the amino acids involved in activity and inhibitor selectivity. Mutations at Asp333 were made in HSPDE4D3 based on mutations that affect rolipram sensitivity in RNPDE4B1. The PDE4D3 Asp-Asn mutant was resistant to inhibition by rolipram as well as several other PDE4 inhibitors tested. These results suggest that this residue is near the inhibitor binding pocket in PDE4D3. Sequence comparison of PDE4 with cGMP-specific PDE proteins shows a conserved aspartic acid at position 333 in PDE4D3 and a conserved asparagine at this position in PDE enzymes that hydrolyze cGMP. Therefore, cGMP hydrolysis by PDE4D3 Asp-Asn was measured. PDE4D3 Asp-Asn hydrolyzes cGMP with kinetic constants similar to those observed for this protein with cAMP (K(m) approximately 20 microM, V(max) approximately 2 micromol AMP/min/mg recombinant protein). Under identical conditions, the K(m) value for cAMP hydrolysis by wild-type PDE4D3 is 3 microM and the V(max) value is 1 micromol AMP/min/mg recombinant protein. In addition, the PDE4D3 Asp-Ala mutant protein could hydrolyze cGMP. Finally, the analogous mutation in HSPDE4B1 (Asp413Asn) also allows hydrolysis of cGMP. These results show that this aspartic acid residue is important in inhibitor binding and nucleotide discrimination and suggest this residue is in the active site of PDE4.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1999

Antithrombotic effects of BCH 2763, a new direct thrombin inhibitor, in a canine model of venous thrombosis.

Deep venous thrombosis (DVT) is a common cardiovascular disease, resulting in significant mortality each year in the United States. Direct thrombin inhibitors represent a new class of drugs that could potentially be better than conventional antithrombotic therapy based on indirect inhibition of coagulation factors with heparin and warfarin. BCH 2763 is a potent, selective bifunctional thrombin inhibitor that blocks both the active catalytic site and the anion binding exosite. The objective of this study is to test the antithrombotic efficacy of BCH 2763 in a canine model of DVT induced through electrolytic injury to the femoral vein. BCH 2763 was administered at three dose levels: 0.125 mg/kg bolus followed by 10 microg/kg/min IV infusion (low-dose; n = 5), 0.25 mg/kg bolus followed by 20 microg/kg/min infusion (mid-dose; n = 5), and 0.75 mg/kg bolus followed by 60 microg/kg/min (high-dose; n = 5). The control group (n = 5) received a 5-ml intravenous bolus of saline followed by a 1 mL/kg/h infusion. The parameters evaluated were changes in activated partial thromboplastin time (aPTT), thrombin time (TT), prothrombin time (PT), time to formation of an occlusive thrombus in the femoral vein, and the amount of venous blood flow delivered over the course of the experiment. There were significant dose-dependent increases in aPTT, TT, and PT in the BCH 2763-treated animals compared with the control group. The time to formation of an occlusive thrombus in the control group averaged 69.6 +/- 9 minutes. Treatment with BCH 2763 prolonged the time to occlusion to 126.4 +/- 13 minutes in the low-dose group, 155.4 +/- 17 minutes in the mid-dose group, and 229 +/- 7 minutes in the high-dose group (80% remained patent for the duration of the study), which were all significantly greater than the controls. Femoral venous blood flow was significantly greater in the mid-dose (51 +/- 8%) and the high-dose (70 +/- 6%) groups compared with the control vessels (22 +/- 3%). In conclusion, the results of this study indicate that BCH 2763 is an effective intravenous antithrombotic agent in the canine electrolytic injury model of venous thrombosis.

Animals↗

PubMed1998

Use of acridine orange in: flow cytometric evaluation of erythropoietic cytotoxicity.

Cytotoxic insult to bone marrow frequently impairs the proliferating and maturational abilities of erythroid cells. Typically, a ratio of enucleated, immature polychromatic erythrocytes (PCE) to mature normochromatic erythrocytes (NCE) is used to assess cytotoxicity in the micronucleus (MN) assay. The effects of cyclophosphamide (CP) on PCE/NCE ratio in rat bone marrow and spleen were assessed by a newly developed flow cytometric procedure using glutaraldehyde-fixed, acridine orange (AO)-stained cells, and compared to manual scoring of PCE/NCE in Wright stained slides. Comparison of methods showed that manual and flow cytometric determination of PCE were not statistically different. Several other parameters of cytotoxicity could be simultaneously assessed because the method allowed use of unfractionated whole bone marrow/spleen cell samples. Absolute numbers of total nucleated cells (TNC), a ratio of TNC to total erythrocytes (TE), and determination of RNA content within the PCE population demonstrated dose- and time-dependent effects with CP treatment. Shifts in RNA content were particularly sensitive, correctly identifying all CP-treated from control specimens, even in those samples where PCE/NCE ratio was similar. The AO methodology provided a more rapid, statistically-superior, and thorough approach in the assessment of bone marrow and spleen cytotoxicity than the conventional manual method of scoring PCE/NCE ratio alone.

Acridine Orange↗

PubMed1998

Use of acridine orange in: flow cytometric assessment of micronuclei induction.

The micronucleus assay is a widely accepted method for evaluation of clastogens and aneugens. In the current study, acridine orange (AO) supravital staining was adapted for flow cytometric usage to assess micronucleated cells in rat bone marrow and spleen. Cyclophosphamide was used as a positive control test compound and results were compared to manual scoring in Wright-stained slides. In bone marrow, both manual and flow cytometric methods demonstrated positive dose response-trends for micronucleated polychromatic erythrocytes (MNPCE). Significant elevations in MNPCE were observed at all doses of cyclophosphamide, and comparisons between methods in bone marrow were not statistically different. The flow cytometric method was more sensitive in spleen samples, showing dose- and time-related increases in micronuclei compared with manual scoring. AO proved to be a sensitive discriminator of RNA and DNA, allowing distinct separation of polychromatic erythrocytes (PCE), normochromic erythrocytes (NCE), total nucleated cells (TNC), and micronucleated populations within both PCE and NCE regions. These results support the use of AO-based flow cytometry to provide a rapid and sensitive indicator of micronuclei inducers.

Acridine Orange↗

PubMed1996

Endothelin A receptor antagonism by PD 156707 does not reduce infarct size after coronary artery occlusion/reperfusion in pigs.

Episodes of myocardial ischemia are associated with increases in cardiac venous plasma endothelin (ET) concentrations, suggesting that ET may play a role in the development of myocardial infarction. The purpose of this study was to determine if selective blockade of ET(A) receptors by PD 156707 reduces infarct size caused by coronary artery occlusion and reperfusion in pentobarbital-anesthetized micropigs. A PD 156707 dose which selectively blocks the ET(A)-mediated vasopressor response, but not the ET(B)-mediated vasodepressor response to i.v. ET-1 challenges (0.3 nmol/kg), was established in dose ranging studies in anesthetized micropigs. In myocardial infarction studies, micropigs received either saline vehicle (n = 7) or PD 156707 (n = 8) at a loading dose of 10 mg/kg/1 hr, followed by a maintenance dose of 7 mg/kg/hr. Coinciding with the start of the maintenance dose, the left anterior descending coronary artery was occluded for 1 hr followed by 3 hr of reperfusion. PD 156707 caused a significant (29 mm Hg) decrease in arterial blood pressure before occlusion. PD 156707 had no effect on infarct size (61.1 +/- 5.6% of the region at risk in the PD 156707 treatment group vs. 70.1 +/- 3.9% in the control group). These results suggest that ET(A) receptor activation does not substantially contribute to coronary artery occlusion/reperfusion-induced myocardial infarction.

Animals↗

PubMed1995

Short-term evaluation of a foraging device for non-human primates.

In the USA, any institution involved in using non-human primates for research has had, for regulatory reasons, to address the psychological needs of these animals. Enriching the environment through the use of foraging devices has been one method and a study was designed to evaluate the short-term effect of a new foraging device on singly-housed cynomolgus monkeys. The study was divided into 3 one-week periods of observation: baseline, device filled with normal ration, and device filled with a novel food. Four behaviours were recorded: foraging, self-directed, hopper feeding, and other behaviours. During the observation periods the device was accepted in preference to the standard hopper style feeder and self-directed behaviours were significantly reduced compared with the baseline period. Changing to a novel food re-kindled interest in the device and reduced the extinguishing effect: i.e. decrease in interest or use of the device. Based on this study, the feeder has been included with several other devices in a rotation programme.

Animal Feed↗

PubMed1992

Malignant tumors in the pituitary gland.

Malignant tumors of the pituitary gland may mimic pituitary adenomas both in clinical presentation and in imaging, and often present with neurologic findings including visual field loss and extraocular movement palsies. We describe a 58-year-old woman without known malignancy who presented with extraocular movement weakness, loss of facial sensation, and a sellar plasmacytoma; a 49-year-old woman with oculomotor palsy, no known malignancy, and rapidly failing vision who had metastatic lung carcinoma; and a 70-year-old woman with metastatic breast carcinoma who presented with rapidly failing vision and a metastasis to the anterior lobe of the pituitary. These cases illustrate several important features of malignancy in the pituitary fossa: that it can mimic a "nonfunctioning" pituitary adenoma in clinical presentation and imaging; that rapidly progressive visual loss, extraocular movement palsies, or facial sensory loss may help to distinguish it from a benign adenoma; and that when the pathologist evaluates an alleged "nonsecretory" or "nonfunctional" adenoma, metastases should be included in the differential diagnosis.

Adenocarcinoma↗

PubMed1991

TGF beta 1 and TGF beta 2 are potential growth regulators for low-grade and malignant gliomas in vitro: evidence in support of an autocrine hypothesis.

Low-grade astrocytomas, anaplastic astrocytomas and glioblastomas in vitro were found to ubiquitously produce the mRNA of transforming growth factor-beta (TGF beta). TGF beta 1 and TGF beta 2 mRNA were expressed to a lesser degree among the hyperdiploid malignant gliomas. By radioreceptor assay of conditioned medium, TGF beta was secreted predominantly in latent form, in both latent and active form, or only in active form within a panel of low-grade and malignant gliomas. The TGF beta receptor (types I, II, and III) was evident among the glioma lines. Many near-diploid gliomas were growth-inhibited by TGF beta 1 and TGF beta 2 in vitro. Most hyperdiploid glioblastomas showed a positive mitogenic response to exogenous TGF beta 1 and TGF beta 2. A synergistic or additive mitogenic interaction with epidermal growth factor and insulin was observed among some. Under serum-free conditions, anti-TGF beta antibody neutralized the expected growth-regulatory effect of endogenous TGF beta, thus establishing the specificity of the response in vitro. TGF beta 1 also enhanced the clonogenicity of certain gliomas which had been growth-stimulated in monolayer. Thus, basic elements in support of an autocrine hypothesis have been demonstrated: TGF beta mRNA was expressed among low-grade and malignant gliomas, TGF beta was secreted in latent and/or active form into conditioned media and appeared to serve as an endogenous regulator of glioma proliferation in vitro. The mitogenic response, either positive or negative, correlated with the degree of anaplasia and karyotypic divergence.

Blotting, Northern↗

PubMed1991

Bilateral breast cancer: one disease or two?

Our purpose was to determine whether bilateral breast cancer depends upon genetic predisposition to multiple tumors or, alternatively, represents two independent sporadic events. Biological concordance of hormone receptors and histopathology in bilateral tumors, family history of breast cancer, age at diagnosis, and survival were evaluated in 88 patients. The immunoreactivity of paired tumors from 51 patients to six different immunocytochemical markers was compared. Neither histologic patterns nor immunocytochemical reactions showed concordance between bilateral tumors. Absence of concordance (other than for estrogen receptors) and lack of associations with positive family history and early age of onset support an interpretation of independent tumor origins and does not suggest a major role for genetic determinants in the majority of cases of bilateral breast cancer.

Adult↗

PubMed1988

Limiting artifact in CT stereotaxic periventricular procedures. Technical note.

One potential source of computerized tomography image artifact during stereotaxic data acquisition is scatter from standard steel-tipped fixation pins as supplied for use with the Brown-Roberts-Wells stereotaxic headframe. In some cases, this can hinder selection of periventricular targets. Replacement of the steel-tipped pins with aluminum-tipped pins, which produce less artifact, helps to facilitate stereotaxic intervention.

Aluminum↗

PubMedDate not supplied

Comparison by PAM fluorometry of photosynthetic activity of nine marine phytoplankton grown under identical conditions.

The photosynthetic activity of marine phytoplankton from five algal classes (Phaeodactylum tricornutum, Skeletonema costatum, Thalassiosira oceanica, Thalassiosira weissflogii, Dunaliella tertiolecta, Mantoniella squamata, Emiliania huxleyi, Pavlova lutheri and Heterosigma akashiwo) was investigated under identical growth conditions to determine interspecies differences. Primary photochemistry and electron transport capacity of individual species were examined by pulse amplitude-modulated (PAM) fluorescence. Although few differences were found in maximal photosystem II (PSII) photochemical efficiency between various species, large differences were noticed in their PSII-photosystem I (PSI) electron transport activity. We found that species such as T. oceanica and M. squamata have much lower photochemical activity than H. akashiwo. It appeared that processes involved in electron transport activity were more susceptible to change during algal evolution compared with the primary photochemical act close to PSII. Large variations in the nonphotochemical energy dissipation event among species were also observed. Light energy required to saturate photosynthesis was very different between species. We have shown that M. squamata and H. akashiwo required higher light energy (>1300 micromol m(-2) s(-1)) to saturate photosynthesis compared with S. costatum and E. huxleyi (ca 280 micromol m(-2) s(-1)). These differences were interpreted to be the result of variations in the size of light-harvesting complexes associated with PSII. These disparities in photosynthetic activity might modulate algal community structure in the natural environment where light energy is highly variable. Our results suggest that for an accurate evaluation of primary productivity from fluorescence measurements, it is essential to know the species composition of the algal community and the individual photosynthetic capacity related to the major phytoplankton species present in the natural phytoplankton assemblage.

Electron Transport↗