EUS-guided biliary drainage with electrocautery-enhanced lumen-apposing metal stent placement should replace PTBD after ERCP failure in patients with distal tumoral biliary obstruction: a large real-life study.

AIMS: In cases of malignant distal biliary obstruction, ERCP is the preferred technique for bile duct drainage. In case of failure, the alternative techniques are percutaneous transhepatic biliary drainage (PTBD) and more recently endoscopic ultrasound-guided biliary drainage. A new type of stent called the electrocautery-enhanced lumen-apposing metal stent (EC-LAMS) has been developed to enable the performance of biliary-enteric anastomosis under EUS-guidance in a single step, without prior bile duct puncture or the need for a guidewire. The aim of our study was to compare the real-life efficacies of PTBD and EUS-BD with the EC-LAMS for cases of ERCP failure in patients with malignant biliary obstruction. METHODS: We performed a monocentric retrospective study comparing PTBD and EUS-BD with the use of electrocautery-enhanced lumen-apposing metal stent in the context of a malignant distal biliary obstruction after ERCP failure. RESULTS: 95 patients were included (50 in EUS-BD group and 45 in PTBD group). The main etiology of malignant obstruction was adenocarcinoma of the head of pancreas (85%). There was a significant difference in favor of endoscopic ultrasound-guided biliary drainage using electrocautery-enhanced lumen-apposing metal stent for the following criteria: clinical success: 89.3% vs. 45.5%; p < 0.0001; procedure-related adverse event rate: 2.12% vs. 22.7%; p = 0.003; duration of post-drainage hospitalization: 3.5 vs. 8.2 days; p < 0.0001, overall survival (median survival): 118.2 vs. 42 days; p = 0.012, overall cost of the strategy per patient: 5098 vs. 9363 euros; p < 0.001. CONCLUSION: Our results are in favor of EUS-BD using electrocautery-enhanced lumen-apposing metal stent in case of ERCP failure for a distal tumor biliary obstruction. Operators performing ERCP for distal tumor biliary obstruction must learn this backup procedure because of its superiority over percutaneous transhepatic biliary drainage in terms of clinical success, safety, cost, and overall survival.

Adherence to online monitoring of patient-reported outcomes by patients with chronic inflammatory diseases: a feasibility study.

OBJECTIVES: The objective of this report is to investigate the feasibility of collecting patient-reported outcomes (PROs) via e-questionnaires delivered to patients with chronic inflammatory diseases (CIDs). METHODS: Consecutive outpatients with a confirmed diagnosis of systemic lupus erythematosus, primary Sjögren's syndrome or inflammatory bowel disease were followed at two medical departments. Patients received monthly e-mails containing the SF36, Hospital Anxiety and Depression scale and an analogue symptom scale over a six-month period. Participation rate, socio-demographic characteristics and patients' satisfaction were analysed. RESULTS: A total of 128 patients were included (79% female; mean age: 42 ± 12 years). Eighty-two per cent of questionnaires were returned. The monthly participation rate ranged from 89% to 77%, with a six-month attrition rate of 13%. The mean completion rate of questionnaires was 98%. Factors significantly associated with increased answer rate were: married/couple status, greater number of children at home and previous participation in online surveys. The main reasons for non-response were: 'too busy to participate' (35%) and 'away from home Internet access' (31%). Overall, 68% of the participants found the study convenient and 96% agreed to continue at a monthly or bimonthly frequency. CONCLUSION: Online home self-assessment of PROs was feasible in the setting of CIDs. Patients were satisfied and willing to continue the survey. The Internet allows immediate and sophisticated presentation of PROs to clinicians. Future studies are warranted to determine how PRO monitoring may contribute to routine care in CIDs and other diseases.

[Non-cirrhotic ascites: pathophysiology, diagnosis and etiology]. / L'ascite non liée à la cirrhose : physiopathologie, diagnostic et étiologies.

Ascites, in 20% of cases, is not linked to liver cirrhosis. The pathophysiology is most often different. The understanding of these pathophysiological mechanisms can lead to etiologic diagnosis. The diagnostic approach is mainly based on the biological study of ascites, especially protein concentration and albumin gradient between serum and ascites. In Western countries, tumors and heart diseases are the predominant causes, while developing countries are mainly concerned by infectious diseases, among which tuberculosis is the leading cause. Other uncommon causes must be recognized, as ascites may be the presenting feature of the disease. Their knowledge will facilitate the therapeutic approach.

Distribution of total DNA and cccDNA in serum and PBMCs may reflect the HBV immune status in HBsAg+ and HBsAg- patients coinfected or not with HIV or HCV.

BACKGROUND: The potential reservoir role of serum and peripheral blood mononuclear cells (PBMCs) for total HBV DNA (tDNA) and cccDNA still remains unknown. MATERIAL AND METHODS: We analyzed tDNA and cccDNA with a single sensitive and validated standardized real-time PCR method in serum and PBMCs in two populations of chronic HBV infection coinfected or not with HCV and/or HIV viruses: a retrospective cohort of 130 HBsAg-negative (HBsAg-) patients with "anti-HBc alone" or anti-HBc and anti-HBs antibodies (Ab) and a cohort of 70 HBsAg-positive patients, 16 of them being prospectively followed under treatment. RESULTS: Among HBsAg- patients, HBV DNA was detected in serum or PBMCs in about half of the cases with various distributions of tDNA and cccDNA: in HIV-negative patients with an "antiHBc alone" profile, tDNA was mostly detected in PBMCs suggesting a possible active role of PBMCs; although cccDNA was not detected in PBMCs in HIV-positive patients, tDNA and cccDNA were mostly observed in serum, suggesting a specific pattern of more "persistent" than "occult" infection in this population. Patients with anti-HBc and anti-HBs Ab harbored tDNA in serum or in PBMCs, regardless of their HIV or HCV status, raising the question of a viral reactivation risk during immunosupression in these patients. Among HBsAg+ patients, tDNA was detected in serum and PBMCs of 88.5% of the cases and cccDNA in 22%. Levels of tDNA in both compartments were highly correlated during treatment, suggesting a passive reservoir role for PBMCs. CONCLUSION: The respective distribution of tDNA and cccDNA in serum and PBMCs may reflect the different immune statuses of the host in HBsAg+ and HBsAg- patients. The frequency of HBV DNA in PBMCs from AgHBs- patients suggests a viral reactivation risk during immunodepression in those patients.

Acute liver toxicity due to methylprednisolone: consider this diagnosis in the context of autoimmunity.

The occurrence of corticosteroid-induced hepatitis is a rare event that has been recently described in the literature. We report the case of an acute cytolytic hepatitis in a patient treated with methylprednisolone for multiple sclerosis associated with an autoimmune thyroid dysfunction. After ruling out other etiologies, we concluded that the acute liver injury was due to steroids, and we analyzed the specific circumstances in the literature where methylprednisolone may have been responsible for acute hepatitis.

[Lead poisoning by fishing sinker ingestion]. / Intoxication par ingestion de plombs de pêche.

INTRODUCTION: Lead colic is a rare cause of abdominal pain. The diagnosis of lead poisoning is most often mentioned in at risk populations (children, psychotic patients). CASE REPORT: We report a 21-year-old man who presented with colicky abdominal pain. Abdominal plain radiograph showed multiple intracolonic metallic bodies. Markedly elevated lead and zinc protoporphyrin serum levels confirmed the diagnosis of lead poisoning. The patient reported that he commonly chewed fishing lead sinker and may sometimes swallow them during the preparation of fishing rod. Clinical outcome was favourable with chelation therapy. CONCLUSION: Lead poisoning following fishing sinker ingestion is very uncommon. Diagnosis may be discussed in the presence of foreign metallic bodies on plain abdominal radiograph and confirmed by high serum level of lead. A prompt treatment with chelation therapy and digestive emptying is usually effective.

Adrenocortical incidentaloma with uncertain prognosis associated with an inadequately treated congenital adrenal hyperplasia.

Large adrenal tumors are rarely associated with adrenal enzymatic deficiency, except in 11-ss-hydroxylase insufficiency. These tumors are exceptionally malignant. We report here the case of a patient with a congenital 21-hydroxylase deficiency (compound heterozygote for two severe mutations in the CYP21A2 gene) untreated for 20 years. His evaluation at 36 years of age showed a four-centimeter mass in the left adrenal gland, with most characteristics suggestive of malignancy (CT and positron emission tomography [PET] scan). We performed a surgical resection that established the diagnosis of adrenocortical tumor of uncertain prognosis (Weiss's score: 3). Even though malignant tumors are unusual in adrenal deficiency, our observation shows the need for a replacement therapy during adulthood, with a regular CT scan follow up in order to diagnose early isolated adrenal adenoma and remove it in case of malignancy suspicion.

[Neck dissection following chemoradiation for node positive head and neck carcinomas]. / Place du curage ganglionnaire après chimioradiothérapie dans les carcinomes épidermoïdes des voies aérodigestives supérieures avec atteinte ganglionnaire initiale (nasopharynx exclu).

The optimal timing and extent of neck dissection in the context of chemoradiation for head and neck cancer remains controversial. For some institutions, it is uncertain whether neck dissection should still be performed upfront especially for cystic nodes. For others, neck dissection can be performed after chemoradiation and can be omitted for N1 disease as long as a complete response to chemoradiation is obtained. The question is debated for N2 and N3 disease even after a complete response as the correlation between radiological and clinical assessment and pathology may not be reliable. Response rates are greater than or equal to 60% and isolated neck failures are less than or equal to 10% with current chemoradiation protocols. Some therefore consider that systematic upfront or planned neck dissection would lead to greater than or equal to 50% unnecessary neck dissections for N2-N3 disease. Positron-emission tomography (PET) scanning to assess treatment response and have shown a very high negative predictive value of greater than or equal to 95% when using a standard uptake value of 3 for patients with a negative PET at four months after the completion of therapy. These data may support the practice of observing PET-negative necks. More evidence-based data are awaited to assess the need for neck dissection on PET. Selective neck dissection based on radiological assessment and peroperative findings and not exclusively on initial nodal stage may help to limit morbidity and to improve the quality of life without increasing the risk of neck failure. Adjuvant regional radiation boosts might be discussed on an individual basis for aggressive residual nodal disease with extracapsular spread and uncertain margins but evidence is missing. Medical treatments aiming at reducing the metastatic risk especially for N3 disease are to be evaluated.

[Regenerative medicine: stem cells, cellular and matricial interactions in the reconstruction of skin and cornea by tissue engineering]. / La médecine régénératrice : les cellules souches, les interactions cellulaires et matricielles dans la reconstruction cutanée et cornéenne par génie tissulaire.

Considering that there is a shortage of organ donor, the aim of tissue engineering is to develop substitutes for the replacement of wounded or diseased tissues. Autologous tissue is evidently a preferable transplant material for long-term graft persistence because of the unavoidable rejection reaction occuring against allogeneic transplant. For the production of such substitutes, it is essential to control the culture conditions for post-natal human stem cells. Furthermore, histological organization and functionality of reconstructed tissues must approach those of native organs. For self-renewing tissues such as skin and cornea, tissue engineering strategies must include the preservation of stem cells during the in vitro process as well as after grafting to ensure the long-term regeneration of the transplants. We described a tissue engineering method named the self-assembly approach allowing the production of autologous living organs from human cells without any exogenous biomaterial. This approach is based on the capacity of mesenchymal cells to create in vitro their own extracellular matrix and then reform a tissue. Thereafter, various techniques allow the reorganization of such tissues in more complex organ such as valve leaflets, blood vessels, skin or cornea. These tissues offer the hope of new alternatives for organ transplantation in the future. In this review, the importance of preserving stem cells during in vitro expansion and controlling cell differentiation as well as tissue organization to ensure quality and functionality of tissue-engineered organs will be discussed, while focusing on skin and cornea.

[Splenic trauma: an unusual complication of colonoscopy with polypectomy]. / Le traumatisme splénique: une complication rare de la coloscopie avec polypectomie.

Nowadays, colonoscopy has become an invaluable tool in the diagnosis and treatment of diseases of the colon and rectum. Colonoscopy is still an invasive exam with several complications. The most common complications are perforation and bleeding, which occur in up to 1% after diagnostic colonoscopy and 3% of patients undergoing therapeutic colonoscopy. Less common complications include pneumothorax, pneumomediastinum, colonic volvulus, hernia incarceration, retroperitoneal abscess and mesenteric tear. Splenic rupture is a rare and potentially lethal colonoscopic complication with less than 45 cases reported in the world. The overall incidence is 0.004%. Mechanisms of injury and available treatment options remain discussed. We present a case of splenic rupture after colonoscopy with polypectomy in a 73-year-old woman managed first with nonoperative treatment and nine days later with surgical treatment. As the indications for colonoscopy expand, including the introduction of mass screening for colorectal cancer, endoscopists should be increasingly aware of that life-threatening complication after colonoscopy and know the emergency treatment.

Chloroplast targeting of phytochelatin synthase in Arabidopsis: effects on heavy metal tolerance and accumulation.

The enzymatically synthesized thiol peptide phytochelatin (PC) plays a central role in heavy metal tolerance and detoxification in plants. In response to heavy metal exposure, the constitutively expressed phytochelatin synthase enzyme (PCS) is activated leading to synthesis of PCs in the cytosol. Recent attempts to increase plant metal accumulation and tolerance reported that PCS over-expression in transgenic plants paradoxically induced cadmium hypersensitivity. In the present paper, we investigate the possibility of synthesizing PCs in plastids by over-expressing a plastid targeted phytochelatin synthase (PCS). Plastids represent a relatively important cellular volume and offer the advantage of containing glutathione, the precursor of PC synthesis. Using a constitutive CaMV 35S promoter and a RbcS transit peptide, we successfully addressed AtPCS1 to chloroplasts, significant PCS activity being measured in this compartment in two independent transgenic lines. A substantial increase in the PC content and a decrease in the glutathione pool were observed in response to cadmium exposure, when compared to wild-type plants. While over-expressing AtPCS1 in the cytosol importantly decreased cadmium tolerance, both cadmium tolerance and accumulation of plants expressing plastidial AtPCS1 were not significantly affected compared to wild-type. Interestingly, targeting AtPCS1 to chloroplasts induced a marked sensitivity to arsenic while plants over-expressing AtPCS1 in the cytoplasm were more tolerant to this metalloid. These results are discussed in relation to heavy metal trafficking pathways in higher plants and to the interest of using plastid expression of PCS for biotechnological applications.

[Role of imaging in the evaluation of axillary nodes and metastatic disease from breast carcinoma]. / Imagerie dans le bilan d'extension ganglionnaire et métastatique du cancer du sein.

Disease staging of patients with breast cancer is based on the probability of metastatic disease, the reliability of complementary examinations, and therapeutic possibilities, evaluated on a cost/benefit basis. For regional disease staging, nodal status can be assessed by ultrasound, and the value of this approach can be optimized by imaging-guided biopsies. Ultrasound examination of nodes upstream of the sentinel node allows determination of the utility of this node and the indications for axillary resection. Work-up of metastatic spread is performed only after evaluation of risk factors for metastasis. Prior to therapy, and in the absence of any clinical warning signs for resectable tumors, there are no indications for imaging, which is reserved solely for locally advanced tumors.

Tumorigenicity of the mixed spindle-epithelioid SP6.5 and epithelioid TP17 uveal melanoma cell lines is differentially related to alpha5beta1 integrin expression.

PURPOSE: It has been suggested that the epithelioid morphology and high aggressiveness that is typical of the uveal melanoma cell line TP17 is dependent on the loss of alpha5beta1 integrin expression at the cell surface. The purpose of the current study was to test this hypothesis in the TP17 cell line and investigate the role this integrin may play in the tumorigenicity of the SP6.5 cells, a mixed spindle-epithelioid culture-type human uveal melanoma that shows tumorigenic properties clearly distinct from that of TP17 cells. METHODS: Expression of the alpha5 integrin subunit was restored in the alpha5-TP17 cell line by stably transfecting the cells with a recombinant plasmid encoding the integrin subunit. Flow cytometry and adhesion assays on fibronectin (FN)-coated culture plates were used to monitor alpha5 expression in the cells. The effect of alpha5 expression on both tumorigenicity and cell proliferation was evaluated in vivo in nude mice. In vitro growth properties of the alpha5(+) TP17 cells was evaluated by cell counting and compared with that of the alpha5 parental TP17 cell line. The influence exerted by the alpha5 integrin subunit on the tumorigenic and proliferative properties of the SP6.5 cells was evaluated in vivo in nude mice by exposing the cells to increasing doses of a blocking antibody directed against the alpha5-subunit before subcutaneous injection, and compared with the results obtained with untreated SP6.5 cells. RESULTS: Expression of the alpha5 integrin subunit in the alpha5-TP17 cells was successfully achieved, as evidenced by both flow cytometry and adhesion assays on FN-coated culture plates. Restoring expression of alpha5 in TP17 cells enhanced epithelioid cell morphology and increased the growth properties of this cell line in vivo. The ability of the SP6.5 cells to yield subcutaneous tumors was found to be concentration dependent and was reduced in a dose-dependent manner when the cells were exposed to the anti-alpha5 blocking antibody. CONCLUSIONS: Restoring expression of alpha5 in the alpha5-negative TP17 uveal melanoma cell line influenced the proliferative properties of these cells but did not alter its tumorigenic potential. In contrast, the ability of the SP6.5 cells to yield tumors in vivo in nude mice appeared to be related to expression of this integrin.

Leaf chlorosis in oilseed rape plants (Brassica napus) grown on cadmium-polluted soil: causes and consequences for photosynthesis and growth.

Brassica napus L. (oilseed rape) was grown from seeds on a reconstituted soil contaminated with cadmium (100 mg Cd kg-1 dry soil), resulting in a marked chlorosis of the leaves which was investigated using a combination of biochemical, biophysical and physiological methods. Spectroscopic and chromatographic analyses of the photosynthetic pigments indicated that chlorosis was not due to a direct interaction of Cd with the chlorophyll biosynthesis pathway. In addition, mineral deficiency and oxidative stress were apparently not involved in the pigment loss. Leaf chlorosis was attributable to a marked decrease in the chloroplast density caused by a reduction in the number of chloroplasts per cell and a change in cell size, suggesting that Cd interfered with chloroplast replication and cell division. Relatively little Cd was found in the chloroplasts and the properties of the photosynthetic apparatus (electron transport, protein composition, chlorophyll antenna size, chloroplast ultrastructure) were not affected appreciably in plants grown on Cd-polluted soil. Depth profiling of photosynthetic pigments by phase-resolved photoacoustic spectroscopy revealed that the Cd-induced decrease in pigment content was very pronounced at the leaf surface (stomatal guard cells) compared to the leaf interior (mesophyll). This observation was consistent with light transmission and fluorescence microscopy analyses, which revealed that stomata density in the epidermis was noticeably reduced in Cd-exposed leaves. Concomitantly, the stomatal conductance estimated from gas-exchange measurements was strongly reduced with Cd. When plants were grown in a high-CO2 atmosphere (4,000 microliters CO2 l-1), the inhibitory effect of Cd on growth was not cancelled, suggesting that the reduced availability of CO2 at the chloroplast level associated with the low stomatal conductance was not the main component of Cd toxicity in oilseed rape.

Can we produce a human corneal equivalent by tissue engineering?

Tissue engineering is progressing rapidly. Bioengineered substitutes are already available for experimental applications and some clinical purposes such as skin replacement. This review focuses on the development of reconstructed human cornea in vitro by tissue engineering. Key elements to consider in the corneal reconstruction, such as the source for epithelial cells and keratocytes, are discussed and the various steps of production are presented. Since one application of this human model is to obtain a better understanding of corneal wound healing, the mechanisms of this phenomenon as well as the function played both by membrane-bound integrins and components from the extracellular matrix have also been addressed. The analysis of integrins by immunohistofluorescence labelling of our reconstructed human cornea revealed that beta(1), alpha(3), alpha(5), and alpha(6) integrin subunits were expressed but alpha(4) was not. Laminin, type VII collagen and fibronectin were also detected. Finally, the future challenges of corneal reconstruction by tissue engineering are discussed and the tremendous applications of such tissue produced in vitro for experimental as well as clinical purposes are considered.

Inhibition by iodoacetamide and acetylene of the H-D-exchange reaction catalyzed by Thiocapsa roseopersicina hydrogenase.

The kinetics of H-D isotope exchange catalyzed by the thermostable hydrogenase from Thiocapsa roseopersicina have been studied by analysis of the exchange between D2 and H2O. The pH dependence of the exchange reaction was examined between pH 2.5 and pH 11. Over the whole pH range, HD was produced at a higher initial velocity than H2, with a marked optimum at pH 5.5; a second peak in the pH profile was observed at around pH 8.5. The rapid formation of H2 with respect to HD in the D2/H2O system is consistent with a heterolytic cleavage of D2 into D+ and an enzyme hydride that can both exchange with the solvent. The H-D-exchange activity was lower in the H2/D2O system than in the D2/H2O system. The other reactions catalyzed by the hydrogenase, H2 oxidation and H2 evolution, are pH dependent; the optimal pH were 9.5 for H2 uptake and 4.0 for H2 production. Treatment of the active form of hydrogenase by iodoacetamide led to a slow and irreversible inhibition of the H-D exchange. When iodo[1-14C]acetamide was incubated with hydrogenase, the radioactive labeling of the large subunit was higher for the enzyme activated under H2 than for the inactive oxidized form. Cysteine residues were identified as the alkylated derivative by amino acid analysis. Acetylene, which inhibits H-D exchange and abolishes the Ni-C EPR signal, protected the enzyme from irreversible inhibition by iodoacetamide. These data indicate that iodoacetamide can reach the active site of the H2-activated hydrogenase from T. roseopersicina. This was not found to be the case with the seleno hydrogenase from Desulfovibrio baculatus (now Desulfomicrobium baculatus). Cysteine modification by iodoacetamide upon activation of the enzyme concomitant with loss of H-D exchange indicates that reductive activation makes at least one Cys residue of the active site available for alkylation.

Light Stress and Oxidative Cell Damage in Photoautotrophic Cell Suspension of Euphorbia characias L.

A photoautotrophic cell-suspension culture of Euphorbia characias L. grown at 70 [mu]mol photons m-2 s-1 was very sensitive to light stress: the gross photosynthesis measured by using a mass spectrometric 16O2/18O2 isotope technique showed a fast decrease at a rather low light intensity of 100 [mu]mol photons m-2 s-1, far below the photosynthetic saturation level. The contribution of activated oxygen species on photosystem II photoinhibition was examined for a given light intensity. A protective effect on gross photosynthesis was observed with 1% oxygen. When light stress was applied to a methyl viologen-adapted cell suspension, photoinhibition was reduced. When 50 [mu]mol L-1 methyl viologen was added, photoinhibition was slightly enhanced. These responses suggested an involvement of superoxide radicals in the photoinhibition process of E. characias photoautotrophic cells. The long-term (16 h) effects of photoinhibition were then studied. Aldehyde (malondialdehyde and 4-hydroxyalcenals) production resulting from lipid peroxidation was stimulated in long-term stressed cells. When 50 [mu]mol L-1 methyl viologen were added, increased aldehyde production was measured. Under 1% oxygen, the aldehyde production was comparable to that of nonstressed cells. The relationship among lipid peroxidation, light intensity, and net photosynthesis suggests that aldehyde production may result from cell death provoked by a prolonged energy deficit due to the inhibition of photosynthesis.

Growth and Photosynthetic Characteristics of Solanum tuberosum Plantlets Cultivated in Vitro in Different Conditions of Aeration, Sucrose Supply, and CO(2) Enrichment.

Growth characteristics, oxygen exchange, and carbohydrate and chlorophyll contents were determined 30 days after subculturing of single node-derived plantlets of Solanum tuberosum cv Haig cultivated in vitro. Cultivation conditions were: (a) photomixotrophy in closed vessel, (b) photomixotrophy in closed vessel on medium supplemented with silver thiosulfate, (c) photomixotrophy in aerated vessel, (d) photoautotrophy in air, (e) photoautotrophy in CO(2)-enriched air. In photomixotrophic conditions, aeration of the vessel enhanced sucrose utilization and had a positive effect on plantlet growth. In photoautotrophic conditions, growth of the plantlets was slow in air and was strongly enhanced by CO(2) enrichment of the atmosphere. Starch to sucrose ratios were higher in plants grown photoautotrophically than in plants grown with sucrose in the medium. Oxygen exchange characteristics on a chlorophyll basis were similar between the plantlets when measured under moderate light, and resembled those of greenhouse plant leaves. In high light, however, plantlets grown photoautotrophically in a CO(2)-enriched atmosphere had higher oxygen exchange rates. We concluded from these results that potato plantlets in vitro in conditions (c), (d), and (e) developed C3-plant photosynthetic characteristics, which were in photoautotrophically grown plantlets comparable to those of field-grown plants.

Comparison of the Oxygen Exchange between Photosynthetic Cell Suspensions and Detached Leaves of Euphorbia characias L.

Using a mass-spectrometric (16)O(2)/(18)O(2)-isotope technique, we compared the nature and the relative importance of oxygen exchange in photomixotrophic (PM) and photoautotrophic (PA) suspensions of Euphorbia characias L. with those in intact leaves of the same species. Young and mature leaves, dividing and nondividing cell suspensions were characterized in short-term experiments. On chlorophyll basis, the gross photosynthetic activities at CO(2) saturating concentration of PA and PM suspensions varied little from those of leaves. On dry weight basis, gross photosynthesis of PA suspensions was equal to that of leaves because of their similar chlorophyll content. This was not the case in PM suspensions where gross photosynthesis was lower and largely varied during the growth cycle. The CO(2) compensation point of PA cells (155-265 parts per million) was much higher than that of leaves (50-80 ppm). Oxygen uptakes were analyzed in terms of mitochondrial respiration, photorespiration and light stimulation of oxygen uptake (LSOU), often identified to Mehlertype reactions. In PA and PM suspensions, mitochondrial respiration rates were higher than in leaves by a factor of 1.5 to 4.5. In PM suspensions, photorespiration and LSOU were observed only in nondividing cells. Photorespiration and LSOU rates were comparable in PA suspensions and leaves. Our results demonstrate that photorespiration of PA suspensions has not been affected by the 2% CO(2) concentration imposed during 2 years of culture.