Fluorometric documentation of increased cutaneous blood flow after topical application of a PGE2 analog in man

The present study employed fiberoptic fluorometry, a noninvasive means of documenting delivery and removal of fluorescein dye, to evaluate the local circulatory changes elicited by topical application of DHV-PGE2 ME, an investigational PGE2 analog. On Day 1, inactive vehicle was applied to a 5 X 4 cm study site on each thigh of healthy volunteer subjects (n = 12). Symmetrical perfusion was confirmed by similar determinations of dye delivery and removal at each site. On Day 2, DHV-PGE2 ME, 30 or 120 micrograms, was applied to one site while inactive vehicle again was applied to the other. After administration of 120 micrograms in a petrolatum vehicle, fluorometry detected a pronounced increase in nutritive perfusion. There was significant acceleration of dye delivery and removal (p less than 0.05 by ANOVA). Less pronounced changes were noted after the lower dose of DHV-PGE2 ME and when the drug was applied in a triethyl citrate vehicle. The local circulatory changes were not accompanied by systemic effects; there were no changes in vital signs or in fluorometric indices at remote sites.     

Cutaneous erythema and blood pressure lowering effects of topically applied 16-vinylprostaglandins

Topically applied 16-vinylprostaglandis demonstrate the property of rapid transit through the skin and a profound effect on the cutaneous vasculature. At low concentrations in the guinea pig and rabbit, 15-deoxy-16-hydroxy-16-vinyl-PGE₂ (DHV-PGE₂) and its methyl ester (DHV-PGE₂Me) elicit a distinct and persistent erythema which is restricted to the area of application and is not associated with a wheal. Skin temperatures are elevated for several hours following application. Accordingly, these compounds may have therapeutic utility in conditions where local blood flow is compromised or where an enhanced blood flow is desired. In the spontaneously hypertensive rat, topically applied DHV-PGE₂ and DHV-PGE₂Me produce a dramatic and persistent lowering of blood pressure. The maximal effects are comparable to those obtained with equal oral or intravenous doses and are maintained for a longer period of time. Moreover, with the topical route, there is no prolongation in the time required for onset of action (3–5 minutes). It appears that while the skin presents only a minimal diffusion barrier to these compounds, a sufficient depot is maintained to give sustained release and prolonged duration. Transdermal delivery of 16-vinyl prostaglandins may offer a convenient means of achieving a clinical antihypertensive effect without the characteristics effects generally asociated with oral or intravascular prostaglandins.     

The effects of a topical PGE2 analogue on global flap ischemia in rats

The present study evaluated the ability of DHV-PGE2ME, a topically effective 16-vinyl prostaglandin E2 analogue, to improve the tolerance of skin flaps to a period of ischemia. DHV-PGE2ME and placebo were applied to bilateral island flaps on 70 anesthetized rats; then the vascular pedicle of each flap was clamped for 10 hours. Treated flaps evidenced significantly better reperfusion, as documented by quantification of fluorescein dye delivery at 90 minutes after clamp release, and they had significantly greater ultimate viability (p less than 0.05, by ANOVA). While less than 3 percent of untreated flaps survived, those treated with 1.75 and 17.5 microgram/cm2 of drug evidenced 76 and 86 percent survival, respectively. Treatment of a given flap did not affect its contralateral mate, since there was no evidence of a systemic effect. Especially since its effect can be limited to the site of application, DHV-PGE2ME should be valuable for the treatment of compromised perfusion in a variety of settings.     

The concentration of 6-keto-prostaglandin F1α is markedly elevated at the site of blastocyst implantation in the rat

The initiation of blastocyst implantation in the rat is indicated by localized increases in endometrial vascular permeability at the sites where blastocysts are present. The concentrations of 6-keto-prostaglandin F_1α (6-keto-PGF_1α), a stable metabolite of prostaglandin I₂ (PGI₂), were measured by gas chromatography-mass spectrometry in the areas of increased endometrial vascular permeability (uterine dye sites), and compared with those in the remainder of the uterus (uterine non-dye sites). For rats killed either on the evening of Day 5 of pregnancy or on the morning of Day 6, measurable amounts of 6-keto-PGF_1α were found in the dye sites of all animals, whereas 1 of 6 and 4 of 6 rats killed on Days 5 and 6, respectively, had undetectable amounts (< 1 ng) in non-dye site tissue. It was estimated that, on average, the concentration of 6-keto-PGF_1α in dye sites on the evening of Day 5 is at least 40-fold that in non-dye sites. The possible role of PGI₂ in the initiation of blastocyst implantation is discussed.     

Biochemical markers for clinical monitoring of tissue perfusion

The assessment and monitoring of the tissue perfusion is extremely important in critical conditions involving circulatory shock. There is a wide range of established methods for the assessment of cardiac output as a surrogate of oxygen delivery to the peripheral tissues. However, the evaluation of whether particular oxygen delivery is sufficient to ensure cellular metabolic demands is more challenging. In recent years, specific biochemical parameters have been described to indicate the status between tissue oxygen demands and supply. In this review, the authors summarize the application of some of these biochemical markers, including mixed venous oxygen saturation (S_vO₂), lactate, central venous–arterial carbon dioxide difference (PCO₂ gap), and PCO₂ gap/central arterial-to-venous oxygen difference (C_a–vO₂) for hemodynamic assessment of tissue perfusion. The thorough monitoring of the adequacy of tissue perfusion and oxygen supply in critical conditions is essential for the selection of the most appropriate therapeutic strategy and it is associated with improved clinical outcomes.

     

Enhanced decolourization of Direct Red-80 dye by the white rot fungus <Emphasis Type="Italic">Phanerochaete chrysosporium</Emphasis> employing sequential design of experiments

Decolourization of Direct Red 80 (DR-80) by the white rot fungus Phanerochaete chrysosporium MTCC 787 was investigated employing sequential design of experiments. Media components for growing the white rot fungus were first screened using Plackett-Burman design and then optimized using response surface methodology (RSM), which resulted in enhancement in the efficiency of dye removal by the fungus. For determining the effect of media constituents on the dye removal, both percent dye decolourization and specific dye removal due to maximum enzyme activity were chosen as the responses from the experiments, and the media constituents glucose, veratryl alcohol, KH₂PO₄, CaCl₂ and MgSO₄ were screened to be the most effective with P values less than 0.05. Central composite design (CCD) followed by RSM in the optimization study revealed the following optimum combinations of the screened media constituents: glucose, 11.9 g l⁻¹; veratryl alcohol, 12.03 mM; KH₂PO₄, 23.08 g l⁻¹; CaCl₂, 2.4 g l⁻¹; MgSO₄, 10.47 g l⁻¹. At the optimum settings of the media constituents, complete dye decolourization (100% removal efficiency) and a maximum specific dye removal due to lignin peroxidase enzyme of 0.24 mg U⁻¹ by the white rot fungus were observed.     

Effect of nutritional conditions on dye removal from textile effluent by <Emphasis Type="Italic">Aspergillus lentulus</Emphasis>

The nutritional conditions supporting growth and maximum dye removal by Aspergillus lentulus have been investigated. Initially a composite media containing yeast extract, glucose and mineral components was used and the effect of various components on dye removal was studied. For maximum dye removal (≈100%), ≥0.5% (w/v) glucose and ≥0.25% (w/v) yeast extract were essential. While glucose played an important role in pellet formation, which in turn was important for dye removal, yeast extract contributed towards higher biomass production. Mineral components (except NH₄NO₃) did not affect dye removal significantly. Next the alternate sources of carbon (molasses, jaggery, starch and sodium acetate) and nitrogen (peptone, urea, ammonium nitrate, sodium nitrate and ammonium chloride) were tested. Among carbon sources, all the sources produced almost complete dye removal in 48 h (more than 97% in 24 h), except sodium acetate (64% in 48 h). All the tested nitrogen sources resulted in >90% dye removal in 48 h. Yeast extract and peptone gave best results with high dye removal rate (9.8 and 8.1 mg/l/h, respectively). However, among the low cost alternates, urea and NH₄Cl came out to be suitable sources due to the high uptake capacity of the biomass produced coupled with high dye removal rate in case of NH₄Cl. Therefore, a combination of urea and NH₄Cl was tested, which produced complete dye removal with a high dye removal rate (10 mg/l/h). Finally the modified composite media containing urea and NH₄Cl as nitrogen sources and glucose as carbon source was utilized for effluent treatment. Results indicated that performance of modified composite media was at par with composite media for supporting growth of A. lentulus and dye removal from the textile effluent.     

Decolorization of anthraquinone dye by Shewanella decolorationis S12

A new species of genus Shewanella, Shewanella decolorationis S12, from activated sludge of a textile-printing wastewater treatment plant, can decolorize Reactive Brilliant Blue K-GR, one kind of anthraquinone dye, with flocculation first. Although S. decolorationis displayed good growth in an aerobic condition, color removal was the best in an anaerobic condition. For color removal, the most suitable pH values and temperatures were pH 6.0–8.0 and 30–37°C under anaerobic culture. More than 99% of Reactive Brilliant Blue K-GR was removed in color within 15 h at a dye concentration of 50 mg/l. Lactate was the suitable carbon source for the dye decolorization. A metal compound, HgCl₂, had the inhibitory effect on decolorization of Reactive Brilliant Blue K-GR, but a nearly complete decolorization also could be observed at a HgCl₂ concentration of 10 mg/l. The enzyme activities, which mediate the tested dye decolorization, were not significantly affected by preadaptation of the bacterium to the dye.     

Characterization of a methane‐utilizing strain and its application for monitoring methane

Aims: To explore new resources of methane‐utilizing micro‐organism and develop a microbial biosensing system for monitoring methane released from natural and semi‐natural ecosystems. Methods and Results: A methane (CH₄)‐utilizing bacterial strain was isolated from paddy soil using CH₄ as the sole carbon source and identified as Klebsiella sp. ME17 by phenotyping and 16S rDNA sequence analysis. The efficiency of CH₄ utilization of strain ME17 was 83·2% by gas chromatography analysis. A microbial biosensing system for CH₄ detection was developed by combining immobilized cells of strain ME17 with a dissolved oxygen sensor. It was found that response time of the system to CH₄ was <90s. The dissolved O₂ consumption increased with increasing CH₄ from 0% to 16·0% (v/v) demonstrating a positive linear relationship with a low detection limit of 0·2% (v/v). The relative standard deviation is 3·48%. Conclusions: Klebsiella sp. ME17 isolate is capable of utilizing CH₄. The microbial biosensing system of strain ME17 has been successfully applied to measure standard CH₄ sample with satisfactory results. Significance and Impact of the Study: This study suggests that certain strains of Klebsiella genus are capable of utilizing CH₄. Our proposed method appears very attractive for CH₄ measurement in coal mine.     

Selective effects of H<Subscript>2</Subscript>O<Subscript>2</Subscript> on cyanobacterial photosynthesis

The sensitivity of phytoplankton species for hydrogen peroxide (H₂O₂) was analyzed by pulse amplitude modulated (PAM) fluorometry. The inhibition of photosynthesis was more severe in five tested cyanobacterial species than in three green algal species and one diatom species. Hence the inhibitory effect of H₂O₂ is especially pronounced for cyanobacteria. A specific damage of the photosynthetic apparatus was demonstrated by changes in 77 K fluorescence emission spectra. Different handling of oxidative stress and different cell structure are responsible for the different susceptibility to H₂O₂ between cyanobacteria and other phytoplankton species. This principle may be potentially employed in the development of new agents to combat cyanobacterial bloom formation in water reservoirs.     

The 9-day CIDR-PG protocol: Incorporation of PGF2α pretreatment into a long-term progestin-based estrus synchronization protocol for postpartum beef cows

A pilot experiment was designed to test the hypothesis that administration of PGF_2α before progestin treatment would allow for a reduced duration of progestin treatment in a long-term progestin-based estrus synchronization protocol. A modified presynchronization treatment was compared with a standard long-term controlled internal drug release (CIDR) treatment, and treatments were compared on the basis of ovarian follicular dynamics, estrous response rate, synchrony of estrus expression, and pregnancy rates resulting from timed artificial insemination (TAI) in postpartum beef cows. Estrous was synchronized for 85 cows, with cows assigned to one of two treatments based on age, days postpartum, and body condition score. Cows assigned to the 14-day CIDR-PG protocol received a CIDR insert (1.38 g progesterone) on Day 0, CIDR removal on Day 14, and administration of PGF_2α (25 mg im) on Day 30. Cows assigned to the 9-day CIDR-PG protocol received PGF_2α concurrent with CIDR insertion on Day 5, PGF_2α concurrent with CIDR removal on Day 14, and administration of PGF_2α on Day 30. In both treatments, split-time AI was performed based on estrous response. At 72 hours after PGF_2α (Day 33), cows having expressed estrus received TAI; cows that failed to express estrus by 72 hours received TAI 24 hours later (96 hours after PGF_2α on Day 34), with GnRH (100 μg im) administered to nonestrous cows. Estrus-detection transmitters were used from CIDR removal until AI to determine onset time of estrus expression both after CIDR removal and after PGF_2α. Ovarian ultrasonography was performed at CIDR removal on Day 14, PGF_2α on Day 30, and AI on Days 33 or 34. At CIDR removal on Day 14, diameter of the largest follicle present on the ovary was similar between treatments. The proportion of cows expressing estrus after CIDR removal tended to be higher (P = 0.09) among cows assigned to the 9-day CIDR-PG treatment (93%; 40 of 43) than among cows assigned to the 14-day CIDR-PG treatment (81%; 34 of 42). After PGF_2α, a significantly higher proportion (P = 0.02) of cows expressed estrus after synchronization with the 9-day CIDR-PG treatment (91%; 39 of 43) than the 14-day CIDR-PG treatment (69%; 29 of 42). Consequently, pregnancy rate to TAI tended to be increased (P = 0.09) among the 9-day CIDR-PG treatment (76.7%; 33 of 43) compared with the 14-day CIDR-PG treatment (59.5%; 25 of 42). In summary, a long-term CIDR-based estrous synchronization protocol for postpartum beef cows was enhanced through administration of PGF_2α at CIDR insertion and CIDR removal.     

In vitro effects of 2‐methoxyestradiol on cell numbers,morphology, cell cycle progression,and apoptosis induction in oesophageal carcinoma cells

The influence of 2‐methoxyestradiol (2‐ME) was investigated on cell numbers, morphology, cell cycle progression, and apoptosis induction in an oesophageal carcinoma cell line (WHCO3). Dose‐dependent studies (1 × 10^?9M–1 × 10^?6M) revealed that 2‐ME significantly reduced cell numbers to 60% in WHCO3 after 72 h of exposure at a concentration of 1 × 10^?6M compared to vehicle‐treated cells. Morphological studies entailing light‐, fluorescent‐, as well as transmission electron microscopy (TEM) confirmed 2‐ME's antimitotic effects. These results indicated hallmarks of apoptosis including cell shrinkage, hypercondensation of chromatin, cell membrane blebbing, and apoptotic bodies in treated cells. Flow cytometric analyses demonstrated an increase in the G₂/M‐phase after 2‐ME exposure; thus preventing cells from proceeding through the cell cycle. β‐tubulin immunofluorescence revealed that 2‐ME caused spindle disruption. In addition, increased expression of death receptor 5 protein was observed further supporting the proposed mechanism of apoptosis induction via the extrinsic pathway in 2‐ME‐exposed oesophageal carcinoma cells. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of the position of the side chain hydroxy group on the gastric antisecretory and antiulcer actions of E1 prostaglandin analogs

The influence of transposing the C-15 hydroxy group of prostaglandin E₁ methyl ester (PGE₁ME) on gastric antisecretory and antiulcer actions was investigated. The compound (±)15-deoxy- 16α,β-hydroxy PGE₁ME (SC-28904) was equipotent to the reference standard PGE₁ME in suppressing histamine-stimulated gastric secretion in the Heidenhain pouch (HP) dog. In contrast to PGE₁ME, SC-28904 was longer acting when administered intravenously and also showed significant oral activity in the histamine-stimulated gastric fistula dog. SC-28904 was also equipotent to PGE₁ME (range of active doses of 0.5 to 5.0 mg/kg, s.c.) in inhibiting forced-exertion gastric ulceration in rats.The compound (±)15-deoxy-17α,β-hydroxy PGE₁ME (SC-30693) was an inactive antisecretory agent in the dog at the 1.0 mg/kg i.v. bolus dose. This dose was 100 times greater than the active antisecretory dose of PGE₁ME. Likewise, SC-30693, when administered subcutaneously at a 5.0 mg/kg dose, was also totally inactive in preventing gastric ulcers induced by forced exertion in rats.The important implications of this work are that some of the receptor sites for the PGE₁ molecule could easily accommodate the side chain hydroxy group either in the C-15 or C-16 position. Moreover, the hydroxy group in the latter position significantly improved the biological activity of PGE₁ME.     

Caleosin-assembled oil bodies as a potential delivery nanocarrier

Encapsulation of hydrophobic agents with nanocarriers is challenging. Therefore, we have sought to use nanoscale artificial oil bodies (NOBs) as an alternative delivery carrier. To constitute NOBs, caleosin (Cal), a structural protein of plant seed oil bodies, was first fused with ZH2 (Cal-ZH2). ZH2 is a bivalent anti-HER2/neu affibody with a high affinity towards the HER2/neu receptor. After overproduction in Escherichia coli, insoluble Cal-ZH2 was isolated and used to assemble NOBs in one step. Consequently, resulting NOBs had a zeta potential around −49 mV and ranged in size from 150 to 200 nm. Upon loading with a hydrophobic fluorescence dye, NOBs were found to be selectively internalized into HER2/neu-positive tumor cells. Further analyses showed that more than 90% cells were invaded by dye-loaded NOBs and the cargo dye was released in cells with time. In addition, the in vitro assay revealed the release of the dye from NOBs in a slow and prolong manner. Overall, these results indicate the potential of Cal-based NOBs as a delivery vehicle.     

Dominating Energy Losses in NiO p‐Type Dye‐Sensitized Solar Cells

Nickel oxide based p‐type dye‐sensitized solar cells (DSCs) are limited in their efficiencies by poor fill factors (FFs). This work explores the origins of this limitation. Transient absorption spectroscopy identifies fast recombination between the injected hole and the dye anion under applied load as one of the predominant reasons for the poor FF of NiO‐based DSCs. A reduced hole injection efficiency, η_INJ, under applied load is found to play an equally important role. Both, the dye regeneration yield, Φ_REG, and η_INJ decrease by approximately 40%–50% when moving from short‐ to open‐circuit conditions. Spectroelectrochemical measurements reveal that the electrochromic properties of NiO are a further limiting factor for the device performance leading to variable light‐harvesting efficiencies, η_LH, under applied load. The peak light‐harvesting efficiency decreases from 63% at short circuit to 57% at 600 mV reducing the FF of NiO DSCs by 5%. This effect is expected to be more pronounced for future devices with higher operating voltages. Incident, photon‐to‐electron conversion efficiency front–back analysis at applied bias is utilized to characterize the interfacial charge recombination. It is found that the recombination between the injected hole and the redox mediator has a surprisingly small effect on the FF.     

Intranasal Microemulsion of Sildenafil Citrate: In Vitro Evaluation and In Vivo Pharmacokinetic Study in Rabbits

The purpose of the present study was to prepare intranasal delivery system of sildenafil citrate and estimate its relative bioavailability after nasal administration in rabbits to attain rapid onset of action with good efficacy at lower doses. Sildenafil citrate saturated solubility was determined in different solvents, cosolvents, and microemulsion systems. For nasal application, sildenafil citrate was formulated in two different systems: the first was a cosolvent system (S3) of benzyl alcohol/ethanol/water/Transcutol/taurodeoxy cholate/Tween 20 (0.5:16.8:47.7:15.9:1:18.1% w/w). The second was a microemulsion system (ME6) containing Oleic acid: Labrasol/Transcutol/water (8.33:33.3:16.66:41.66% w/w). The prepared systems were characterized in relation to their clarity, particle size, viscosity, pH, and nasal ciliotoxicity. In vivo pharmacokinetic performance of the selected system ME6 (with no nasal ciliotoxicity) was evaluated in a group of six rabbits in a randomized crossover study and compared to the marketed oral tablets. The targeted solubility (>20 mg/ml) of sildenafil citrate was achieved with cosolvent systems S1, S3, and S5 and with microemulsion systems ME3–ME6. The saturated solubility of sildenafil citrate in cosolvent system S3 and microemulsion system ME6 were 22.98 ± 1.26 and 23.79 ± 1.16 mg/ml, respectively. Microemulsion formulation ME6 showed shorter t _max (0.75 h) and higher AUC_(0-∞) (1,412.42 ng h/ml) compared to the oral tablets which showed t _max equals 1.25 h and AUC_(0-∞) of 1,251.14 ng h/ml after administration to rabbits at dose level of 5 mg/kg. The relative bioavailability was 112.89%. In conclusion, the nasal absorption of sildenafil citrate microemulsion was found to be fast, indicating the potential of nasal delivery instead of the conventional oral administration of such drug.     

Chronological approach of diet-induced alterations in muscle mitochondrial functions in rats

Objective: Mitochondrial dysfunction might predispose individuals to develop insulin resistance. Our objective was to determine whether mitochondrial dysfunction or insulin resistance was the primary event during high‐fat (HF) diet. Research Methods and Procedures: Rats were fed an HF diet for 0, 3, 6, 9, 14, 20, or 40 days and compared with control. Soleus and tibialis muscle mitochondrial activity were assessed using permeabilized fiber technique. Insulin [area under the curve for insulin (AUC_I)] and glucose [area under the curve for glucose (AUC_G)] responses to intraperitoneal glucose tolerance test as well as fasting plasma non‐esterified fatty acids (NEFAs), triglyceride, and glycerol concentrations were determined. Results: AUC_I and AUC_G were altered from Day 6 (p < 0.01 vs. Day 0). In soleus, oxidative phosphorylation (OXPHOS) activity was transiently enhanced by 26% after 14 days of HF diet (p < 0.05 vs. Day 0) conjointly with 62% increase in NEFA concentration (p < 0.05 vs. Day 0). This was associated with normalized AUC_G at Day 14 and with a decline of plasma NEFA concentration together with stabilization of intra‐abdominal adiposity at Day 20. Prolongation of HF diet again caused an increase in plasma NEFA concentration, intra‐abdominal adiposity, AUC_I, and AUC_G. At Day 40, significant decrease in OXPHOS activity was observed in soleus. Discussion: Mitochondria first adapt to overfeeding in oxidative muscle limiting excess fat deposition. This potentially contributes to maintain glucose homeostasis. Persistent overfeeding causes insulin resistance and results in a slow decline in oxidative muscle OXPHOS activity. This shows that the involvement of mitochondria in the predisposition to insulin resistance is mainly due to an inability to face prolonged excess fat delivery.     

Progesterone enhances in vitro development of bovine embryos

Increased pregnancy rates in cattle given progesterone (P₄) prior to 5 d after breeding have recently been reported. The objective was to determine if this increase in pregnancy rate could be attributed to a direct positive effect of P₄ on the developing embryo. In Experiment 1, 280 bovine oocytes were inseminated in vitro and at Day 3 (insemination = Day 0), good quality 8 cell embryos (n = 206) were randomly allocated to be cultured in either CR1aa+serum with 0 or ∼15 ng/mL (n = 102 and n = 104, respectively). In Experiment 2, 881 bovine oocytes were used; on Day 3, good quality 8 cell embryos (n = 511) were randomly allocated to either the control (CR1aa+FCS, n = 168), vehicle (CR1aa + FCS + ethanol, n = 170), or P₄ treatment (CR1aa + FCS + ∼15 ng/mL P₄ in ethanol, n = 173). On Day 7, in both experiments, there were increased numbers of blastocysts developing in the P₄ group (Experiment 1, 59% and Experiment 2, 71%) compared to the vehicle (Experiment 2, 53%) or control (40 and 62% in Experiments 1 and 2, respectively). The addition of P₄ (8%) stimulated the rate of embryo development (early blastocysts or more advanced stages on Day 6) compared to vehicle (3%) and control (0%) and the P₄ group had more hatched or hatching blastocysts (33%) on Day 9 compared to the control or vehicle group (21 or 22%). Additionally, the P₄ group had greater embryo diameter and significantly more Grade 1 blastocysts on Day 7. In conclusion, P₄ had a direct, positive effect on developing bovine embryos cultured in vitro.     

Dependence of chlorophyll P700 redox transients during the induction period on the transmembrane distribution of protons in chloroplasts of pea leaves

Differential absorbance measurements and fluorometry were applied to examine the impact of dicyclohexylcarbodiimide (DCCD, an inhibitor of H⁺ conductance in thylakoid membranes) and nigericin (a K⁺/H⁺ antiporter) on photoinduced redox state transients of chlorophyll P700 and the induction curves of chlorophyll fluorescence in pea (Pisum sativum L., cv. Premium) leaves. The treatment of leaves with DCCD strongly modified the kinetics of P700⁺ absorbance changes (ΔA ₈₁₀) by promoting rapid photooxidation of P700. These characteristic changes in ΔA ₈₁₀ induction kinetics and P700⁺ accumulation did not appear when the leaves were treated with DCCD in the presence of nigericin. In addition to opposite modifications of ΔA ₈₁₀ kinetics evoked by permeability-modifying agents, the fluorescence induction curves differed conspicuously depending on leaf incubation in DCCD solutions with or without nigericin. The observed modifications of fluorescence induction curves and ΔA ₈₁₀ indicate that DCCD suppresses electron transport from photosystem II (PSII) to P700, whereas this inhibition is removed by nigericin. The results suggest that slowing down of the electron transport rate in the presence of DCCD was caused by elevation of ΔpH in thylakoids. The prevention of pH gradient formation in the presence of protonophore lowered also the steady-state P700⁺ level in far-red irradiated leaves and accelerated the subsequent dark reduction of P700. These findings indicate that PSI-driven cyclic electron flow is accelerated after the removal of the pH gradient.     

Photosynthetic oxygen exchange in C4 grasses: the role of oxygen as electron acceptor

C₄ grasses of the NAD‐ME type (Astrebla lappacea, Eleusine coracana, Eragrostis superba, Leptochloa dubia, Panicum coloratum, Panicum decompositum) and the NADP‐ME type (Bothriochloa bladhii, Cenchrus ciliaris, Dichanthium sericeum, Panicum antidotale, Paspalum notatum, Pennisetum alopecuroides, Sorghum bicolor) were used to investigate the role of O₂ as an electron acceptor during C₄ photosynthesis. Mass spectrometric measurements of gross O₂ evolution and uptake were made concurrently with measurements of net CO₂ uptake and chlorophyll fluorescence at different irradiances and leaf temperatures of 30 and 40 °C. In all C₄ grasses gross O₂ uptake increased with increasing irradiance at very high CO₂ partial pressures (pCO₂) and was on average 18% of gross O₂ evolution. Gross O₂ uptake at high irradiance and high pCO₂ was on average 3.8 times greater than gross O₂ uptake in the dark. Furthermore, gross O₂ uptake in the light increased with O₂ concentration at both high CO₂ and the compensation point, whereas gross O₂ uptake in the dark was insensitive to O₂ concentration. This suggests that a significant amount of O₂ uptake may be associated with the Mehler reaction, and that the Mehler reaction varies with irradiance and O₂ concentration. O₂ exchange characteristics at high pCO₂ were similar for NAD‐ME and NADP‐ME species. NAD‐ME species had significantly greater O₂ uptake and evolution at the compensation point particularly at low irradiance compared to NADP‐ME species, which could be related to different rates of photorespiratory O₂ uptake. There was a good correlation between electron transport rates estimated from chlorophyll fluorescence and gross O₂ evolution at high light and high pCO₂.