Photochemical Inhibition Research Articles

Effects of seawater acidification and solar ultraviolet radiation on photosynthetic performances and biochemical compositions of Rhodosorus sp. SCSIO-45730

Ocean acidification (OA) caused by rising atmospheric CO2 concentration and solar ultraviolet radiation (UVR) resulting from ozone depletion may affect marine organisms, but little is known regarding how unicellular Rhodosorus sp. SCSIO-45730, an excellent species resource containing various biological-active compounds, responds to OA and UVR. Therefore, we conducted a factorial coupling experiment to unravel the combined effects of OA and UVR on the growth, photosynthetic performances, biochemical compositions and enzyme activities of Rhodosorus sp. SCSIO-45730, which were exposed to two levels of CO2 (LC, 400 μatm, current CO2 level; HC, 1000 μatm, future CO2 level) and three levels of UVR (photosynthetically active radiation (PAR), PAR plus UVA, PAR plus UVB) treatments in all combinations, respectively. Compared to LC treatment, HC stimulated the relative growth rate (RGR) due to higher optimum and effective quantum yields, photosynthetic efficiency, maximum electron transport rates and photosynthetic pigments contents regardless of UVR. However, the presence of UVA had no significant effect but UVB markedly reduced the RGR. Additionally, higher carbohydrate content and lower protein and lipid contents were observed when Rhodosorus sp. SCSIO-45730 was cultured under HC due to the ample HCO3− applications and active stimulation of metabolic enzymes of carbonic anhydrase and nitrate reductase, thus resulting in higher TC/TN. OA also triggered the production of reactive oxygen species (ROS), and the increase of ROS coincided approximately with superoxide dismutase and catalase activities, as well as phenols contents. However, UVR induced photochemical inhibition and damaged macromolecules, making algal cells need more energy for self-protection. Generally, these results revealed that OA counteracted UVR-related inhibition on Rhodosorus sp. SCSIO-45730, adding our understanding of the red algae responding to future global climate changes.

Physiological approach to decipher the drought tolerance of a soybean genotype from Brazilian savana

Drought is one of the major constraints for soybean production in Brazil. In this study we investigated the physiological traits of two soybean parental genotypes under progressive soil drying and rewetting. The plants were evaluated under full irrigation (control) conditions and under water deficit imposed by suspending irrigation until the plants reached predawn leaf water potentials (Ψam) of −1.0 MPa (moderate) and −1.5 MPa (severe). Physiological analyses showed that these genotypes exhibit different responses to water deficit. The Embrapa 48 genotype reached moderate and severe water potential two days after the BR16 genotype and was able to maintain higher levels of A, ETR and ΦPSII even under deficit conditions. This result was not related to changes in gs, 13C isotopic composition and presence of a more efficient antioxidant system. In addition, Fv/Fm values did not decrease in Embrapa 48 genotype in relation to irrigated condition showing that stress was not causing photochemical inhibition of photosynthesis. The greater reduction in the relative growth of the shoots, with concomitant greater growth of the root system under drought, indicates that the tolerant genotype is able to preferentially allocated carbon to the roots, presenting less damage to photosynthesis. Therefore, the physiological responses revealed that the tolerant genotype postponed leaf dehydration by a mechanism involving a more efficient use and translocation of water from root to shoot to maintain cell homeostasis and photosynthetic metabolism under stress.

Influence of fluctuating irradiance on photosynthesis, growth and community structure of estuarine phytoplankton under increased nutrients and acidification

Estuaries represent the interface between riverine and marine ecosystems and they are among the most productive areas on Earth; thus it is of utmost importance to understand their functioning in a global change scenario. So far, it is virtually unknown how the interaction between nutrient inputs, acidification and fluctuating light regimes could alter photosynthesis, growth, and phytoplankton structure in the end members (i.e., river and sea) of estuaries. Using the Chubut river estuary (Argentina) as a model ecosystem, we conducted experimentation during the austral summer (i.e., the windy season, February of 2016) with both, river and seawater phytoplankton communities to assess these topics. We evaluated the impact of fluctuating irradiance (static vs. mixed conditions) using short- (<one day) and mid-term acclimation (five days) and mimicking scenarios of higher acidification and nutrients (Future) as compared with an unmodified Present. The growth of both communities increased significantly under the Future as compared to the Present scenario, but mixing decreased growth only in seawater phytoplankton. Small centric diatoms (mainly Thalassiosira spp.) co-dominated with unidentified flagellates in the seawater, but the relative abundance of diatoms was higher in the Future as compared with the Present scenario. Diatoms and cryptophytes co-dominated in the river at the end of the experiments for both static and mixed conditions. Net primary productivity (NPP) decreased in the Future scenario and this was coupled with higher inhibition (k) of photosystem II (PSII), in both communities. Our results indicate that fluctuating irradiance, under a future global change scenario, as simulated here, has a significant impact on the structure and growth of seawater phytoplankton, together with increases in photochemical inhibition and decreases in NPP. However, these changes are much smaller in the river phytoplankton. Thus, the overall effects of mixing on the trophodynamics of the area will be more important at the sea than in the river end of the estuary.

Fragmentation reduces severe drought impacts on tree functioning in holm oak forests

Fragmentation and increased summer drought are two main threats to Mediterranean forests. Forest fragmentation has many negative impacts on forests but could attenuate water stress on Mediterranean species by reducing intraspecific competition or improving soil properties at forest edges. However, little is known about the combined effects of drought and fragmentation on tree functioning. We evaluated the effect of forest fragmentation on tree functioning under severe drought periods in continental holm oak forests (Quercus ilex). We monitored the functional response of focal trees before and during summer drought in two regions of the Iberian Peninsula with contrasting climates. Forest interiors, edges and small forest fragments were compared. Predawn leaf water potential (Ψpd), leaf stomatal conductance to water vapor (gs), maximum leaf photochemical efficiency (Fv/Fm), ground (Fo) and maximum (Fm) fluorescence in dark adapted, fully-developed leaves were assessed in the field. Trees located at forest interiors and edges showed strong stomatal closure and clear symptoms of photochemical inhibition, revealing that the trees were operating at predawn water potential beyond tolerance thresholds. In contrast, trees located in small forest fragments were able to maintain high levels of functionality for all ecophysiological parameters during the drought. These differences in tree functioning among fragments were more noticiable in the driest region. Our results prove that forest fragmentation attenuates drought impacts on tree functioning, and that these positive effects become more important during extremely dry periods. These novel findings are essential for realistic predictions of the functionality of fragmented forests under increasing and more severe droughts.

Photochemical inhibition of Trichophyton rubrum by different compoundings of curcumin.

Recently, we had shown that conidia-derived growth of many dermatophytes can be inhibited by curcumin plus exposure to visible light. This method of photo inactivation should be developed further aiming for an option to stop mycelial growth in superficial tinea. Wells of microtitre plates were inoculated with either mycelial or conidial elements collected from 5 strains of Trichophyton rubrum. Then either micellar curcumin or curcumin dissolved with DMSO was added and after 20min the wells were filled up with Sabouraud broth. Thereafter the assays were irradiated once with visible light (wave length 420nm, 20J/cm2 ) and fungal growth was monitored photometrically. Identical effects were measured with conidia and mycelial elements of all 5 T.rubrum strains. Curcumin dissolved with DMSO plus irradiation had a marked dose-dependent inhibitory effect on fungal growth that was almost complete with 5.0mg/L (P<.01) over a period of 9days. In contrast, the same procedure with micellar curcumin had no inhibitory effect on growth obtained from conidia or mycelial elements. Mycelial elements of T.rubrum and its conidia are equally sensitive to photochemical inactivation with curcumin and the galenic compounding of curcumin is essential to achieve this photochemical effect.

The effect on photosynthesis and osmotic regulation in Beta vulgaris L. var. Flavescens DC. by salt stress

This study was to investigate the effect of salt stress on physiological characteristics such as plant growth, photosynthesis, solutes related to osmoregulation of Beta vulgaris. A significant increase of dry weight was observed in 50 mM and 100 mM NaCl. The contents of Chl a, b and carotenoid were lower in NaCl treatments than the control. On 14 day after NaCl treatment, photosynthetic rate (PN), the transpiration rate (E) and stomatal conductance of CO2 (gs) were reduced by NaCl treatment. On 28 day after NaCl treatment, the significant reduction in g s and E was shown in NaCl 200 mM. However, PN and water use efficiency (WUE) in all NaCl treatments showed higher value than that of control. Total ion contents (TIC) and osmolality were higher than the control. On 14 day after treatment, the contents of proline (Pro) increased signifi cantly in 200 mM and 300 mM NaCl concentration compared with control, whereas on 28 day in all treatments it was lower than that of the control. The contents of glycine betaine (GB) increased with the increase of NaCl concentration. The contents of Na + , Cl , GB, osmolality and TIC increased with the increase of NaCl concentrations. These results suggested that under severe NaCl stress conditions, NaCl treatment did not induce photochemical inhibition on fluorescence in the leaves of B. vulgaris, but the reduction of chlorophyll contents was related in a decrease in leaf production. Furthermore, increased GB as well as Na + and Cl contents resulted in a increase of osmolality, which can help to overcome NaCl stress.

Ocean acidification alters the photosynthetic responses of a coccolithophorid to fluctuating ultraviolet and visible radiation.

Mixing of seawater subjects phytoplankton to fluctuations in photosynthetically active radiation (400-700 nm) and ultraviolet radiation (UVR; 280-400 nm). These irradiance fluctuations are now superimposed upon ocean acidification and thinning of the upper mixing layer through stratification, which alters mixing regimes. Therefore, we examined the photosynthetic carbon fixation and photochemical performance of a coccolithophore, Gephyrocapsa oceanica, grown under high, future (1,000 μatm) and low, current (390 μatm) CO₂ levels, under regimes of fluctuating irradiances with or without UVR. Under both CO₂ levels, fluctuating irradiances, as compared with constant irradiance, led to lower nonphotochemical quenching and less UVR-induced inhibition of carbon fixation and photosystem II electron transport. The cells grown under high CO₂ showed a lower photosynthetic carbon fixation rate but lower nonphotochemical quenching and less ultraviolet B (280-315 nm)-induced inhibition. Ultraviolet A (315-400 nm) led to less enhancement of the photosynthetic carbon fixation in the high-CO₂-grown cells under fluctuating irradiance. Our data suggest that ocean acidification and fast mixing or fluctuation of solar radiation will act synergistically to lower carbon fixation by G. oceanica, although ocean acidification may decrease ultraviolet B-related photochemical inhibition.

Influence of seasonal variables associated with climate change on photochemical diurnal cycles of marine phytoplankton from Patagonia (Argentina)

The effects of temperature and ultraviolet radiation (UVR; 280–400 nm) on seasonal succession in phytoplankton assemblages of Patagonia (Argentina) were studied in the context of global change. Samples collected during pre‐bloom, bloom onset, bloom, and spring were exposed to in situ and increased (+4°C) temperatures and solar radiation with and without UVR. Daily cycles of effective photochemical quantum yield exhibited a pattern of high values in the morning, decreasing towards noon, and increasing in the afternoon. The decrease in yields towards noon as the season progressed increased from 30% in the pre‐bloom to 80% in the spring; in the latter there were significant differences between radiation treatments under both temperature conditions. The highest inhibition rates were during the bloom, whereas the highest recovery rates were during the spring. Inhibition rates were generally higher in treatments exposed to UVR in comparison to photosynthetically active radiation‐only treatments and some stages of the succession exhibited an additional temperature effect. Increasing temperatures had little effect on pre‐bloom communities but helped to counteract the magnitude of the yield decrease during the bloom onset. However, during the bloom and in the spring, temperature and UVR acted synergistically, increasing the overall photochemical inhibition. Feedback mechanisms of increased temperatures causing a shallower mixing depth will expose phytoplankton to higher radiation, which will have a negative effect on the bloom and on spring assemblages. Due to the differential effects of solar UVR and increased temperature on phytoplankton, future studies should consider the repercussions on higher trophic levels.

Photochemical Corrosion Inhibition of Mild Steel in Acid Mine Water

Abstract The corrosion inhibition of mild steel in acid mine water of pH 2.5 containing ferric and cupric ions with inhibitors such as urea ([NH2]2CO), guanylurea sulfate (C4H12N8O2·H2SO4), benzotriazole (C6H5N3), butylamine (C4H11N), hexadecyl pyridinium chloride (C21H38ClN·H2O), thiourea (CH4N2S), and potassium oxalate (K2C2O4·H2O) was studied. Thiourea and potassium oxalate gave 77% and 93% inhibition, respectively. Thiourea reduced ferric ions in solution and produced a sulfide film that caused hydrogen embrittlement. Corrosion inhibition by potassium oxalate was photosensitive due to the formation of a trisoxalato iron complex followed by photodecomposition to β-ferrous oxalate and its deposition on the steel sample, thereby inhibiting the corrosion of the steel. The mechanism of this first example of photochemical inhibition is postulated.

Chromophore‐assisted light inactivation of pKi‐67 leads to inhibition of ribosomal RNA synthesis

Expression of the nuclear Ki-67 protein (pKi-67) is strongly associated with cell proliferation. For this reason, antibodies against this protein are widely used as prognostic tools for the assessment of cell proliferation in biopsies from cancer patients. Despite this broad application in histopathology, functional evidence for the physiological role of pKi-67 is still missing. Recently, we proposed a function of pKi-67 in the early steps of ribosomal RNA (rRNA) synthesis. Here, we have examined the involvement of pKi-67 in this process by photochemical inhibition using chromophore-assisted light inactivation (CALI). Anti-pKi-67 antibodies were labelled with the fluorochrome fluorescein 5(6)-isothiocyanate and were irradiated after binding to their target protein. Performing CALI in vitro on cell lysates led to specific cross-linking of pKi-67. Moreover, the upstream binding factor (UBF) necessary for rRNA transcription was also partly subjected to cross-link formation, indicating a close spatial proximity of UBF and pKi-67. CALI in living cells, using micro-injected antibody, caused a striking relocalization of UBF from foci within the nucleoli to spots located at the nucleolar rim or within the nucleoplasm. pKi-67-CALI resulted in dramatic inhibition of RNA polymerase I-dependent nucleolar rRNA synthesis, whereas RNA polymerase II-dependent nucleoplasmic RNA synthesis remained almost unaltered. Our data presented here argue for a crucial role of pKi-67 in RNA polymerase I-dependent nucleolar rRNA synthesis.

Flow injection fluorimetric determination of L-dopa and dopamine based on a photochemical inhibition process

An automatic procedure has been developed for the determination of L-dopa and dopamine. It is based on the strong inhibition of the photochemical reaction between thionine blue and ethylenediamine-tetraacetic acid by these catecholamines. The proposed flow-injection method allows for the fluorimetric determination of L-dopa in the range of 1.9–98 µg mL−1 and that of dopamine in the range of 1.9–75 µg mL−1 with a sampling frequency of 35 samples h−1. The method was applied successfully to the determination of dopamine in pharmaceutical preparations.

Free radical attenuation prevents thrombosis and enables photochemical inhibition of vein graft intimal hyperplasia

Objective Photodynamic therapy (PDT) inhibits post-interventional stenosis in balloon-injured arteries, but causes thrombosis when applied to vein grafts. This may result from added free radicals produced during the hypoxia-reperfusion injury of vein graft implantation. The purposes of this study were to determine whether a free radical scavenger could inhibit vein graft thrombosis, enabling PDT to inhibit intimal hyperplasia; and to investigate the role of neutrophils, also a source of radicals, in this setting. Methods Jugular vein bypass grafts of the common carotid artery were performed in rats. PDT was administered in situ to the vein graft and artery in the presence or absence of deferoxamine (DFX), an OH − scavenger. Results PDT alone induced thrombosis in all untreated vein grafts. DFX administration or inhibition of neutrophil adhesion to the graft prevented PDT-induced vein graft thrombosis. Moreover, DFX given together with PDT significantly decreased vein graft intimal hyperplasia (0.010 mm 2 ± 0.005 mm 2; P < .002) as compared with DFX alone (0.113 mm 2 ± 0.009 mm 2) or untreated control animals (0.112 ± 0.007 mm 2). Conclusions OH − radicals and neutrophils both have key roles in PDT-induced vein graft thrombosis. By inhibiting free radical production or neutrophil adhesion to the graft, adequate PDT can be administered for successful inhibition of vein graft intimal hyperplasia.

Tolerance of Antarctic cyanobacterial mats to enhanced UV radiation

To assess the biological implications of ozone depletion over the Antarctic Peninsula, the ultraviolet (UV) regime of two Antarctic cyanobacterial communities (composed of Leptolyngbya sp. and Phormidium sp.) was manipulated using screens that cut out UV radiation and a lamp which enhanced the dose of UV-B radiation (280–315 nm). The biological response of the cyanobacterial mats was monitored by measurement of chlorophyll fluorescence and pigment concentrations. The Leptolyngbya mat showed significant photochemical inhibition due to increased UV-B relative to photosynthetically active radiation (400–700 nm). The effect of UV on the Phormidium mat was less pronounced and dependent on the method of analysis: significantly lower photochemical yields were observed in UV-enhanced Phormidium mats compared to UV-excluded treatment, but if the yield data relative to the time zero control were considered then no effect of UV enhancement was observed. The Phormidium mat contained over 25 times the absolute concentration of UV-protecting mycosporine-like amino acid (MAA) and double the concentration of carotenoids compared to the Leptolyngbya mat, but the latter contained a higher ratio of carotenoids+MAAs to chlorophyll. There were no significant treatment-related changes in the concentrations of MAA, carotenoids and chlorophyll a in the Phormidium mat. The Leptolyngbya mat showed significantly lower chlorophyll a concentrations under UV enhancement, which could account for the lower photochemical yield in this sample. Our results show that different cyanobacterial species have differing photochemical sensitivity to UV-B radiation, which may confer a subtle advantage to the UV-B tolerant species over the less tolerant type during a period of high UV-B irradiance.

Tolerance of Antarctic cyanobacterial mats to enhanced UV radiation

To assess the biological implications of ozone depletion over the Antarctic Peninsula, the ultraviolet (UV) regime of two Antarctic cyanobacterial communities (composed of Leptolyngbya sp. and Phormidium sp.) was manipulated using screens that cut out UV radiation and a lamp which enhanced the dose of UV-B radiation (280–315 nm). The biological response of the cyanobacterial mats was monitored by measurement of chlorophyll fluorescence and pigment concentrations. The Leptolyngbya mat showed significant photochemical inhibition due to increased UV-B relative to photosynthetically active radiation (400–700 nm). The effect of UV on the Phormidium mat was less pronounced and dependent on the method of analysis: significantly lower photochemical yields were observed in UV-enhanced Phormidium mats compared to UV-excluded treatment, but if the yield data relative to the time zero control were considered then no effect of UV enhancement was observed. The Phormidium mat contained over 25 times the absolute concentration of UV-protecting mycosporine-like amino acid (MAA) and double the concentration of carotenoids compared to the Leptolyngbya mat, but the latter contained a higher ratio of carotenoids+MAAs to chlorophyll. There were no significant treatment-related changes in the concentrations of MAA, carotenoids and chlorophyll a in the Phormidium mat. The Leptolyngbya mat showed significantly lower chlorophyll a concentrations under UV enhancement, which could account for the lower photochemical yield in this sample. Our results show that different cyanobacterial species have differing photochemical sensitivity to UV-B radiation, which may confer a subtle advantage to the UV-B tolerant species over the less tolerant type during a period of high UV-B irradiance.

Application of Photochemical Inhibition to the Fluorometric Determination of Nitroprusside in a Flow-Injection System

An automatic procedure for the determination of nitroprusside has been developed. It is based on the strong quenching effect of the nitroprusside on the photochemical reaction between phloxin and ethylenediaminetetraacetic acid. The proposed flow-injection method allows the fluorimetric determination of nitroprusside in the range 6 × 10−6-7 × 10−5M with a sampling frequency of 35 samples per hour. The method has been applied to the determination of the nitroprusside in human serum and pharmaceutical preparations.

Application of photochemical inhibition in flow injection systems: Determination of epinephrine and L-dopa

An automated procedure for the photochemical determination of epinephrine and L-dopa has been developed. It is based on the strong inhibition by these catecholamines on the photochemical reaction between phloxin and ethylenediaminetetraacetic. The proposed flow-injection method allows the fluorimetric determination of epinephrine in the range 1.9–26.4 μg/ml and of L-dopa in the range of 1.5–12.7 μg/ml, with a sampling frequency of 35 samples/hr. The method was applied successfully to the determination of body catecholamines in pharmaceutical preparations.

The unpolymerized form of tubulin is the target for microtubule inhibition by photoactivated tetra(4-sulfonatophenyl)porphine

Several porphyrins, including tetra(4-sulfonatopheyl)porphine, sensitize cells to photoinactivation. The treatment leads to an accumulation of cells in mitosis, directly or indirectly due to a perturbation of the mitotic spindle. The present work relates to the target for this mode of action. Cells incubated with tetra(4-sulfonatophenyl)porphine were exposed to light and the microtubules were quantified 30 min after light exposure. The amount of microtubules decreased with increasing fluences. The reduction in the amount of microtubules after light exposure was enhanced by prior treatment with nocodazole (1 μg/ml for 20 min) or low temperature (1°C for 60 min). When nocodazole was combined with the photochemical treatment the extent of the inhibition of microtubule formation was dose-dependent only for the lowest fluences applied. Additional light exposure did not further reduce the amount of microtubules 30 min after light exposure. The results presented indicate that the unpolymerized fraction of tubulin is the target for photochemical inhibition of microtubule formation.

Photochemical inhibition of the reaction of copper(II) peptide complexes with molecular oxygen

Copper(II) accelerates the oxidation of tetrapeptides by O2 in neutral solution, but light (λ < 420 nm) has the novel effect of inhibiting the reaction.

The inhibition of photochemical smog—III. Inhibition by Diethylhydroxylamine, N-methylaniline, triethylamine, diethylamine, ethylamine and ammonia

Additional inhibitors for the conversion of NO to NO 2 in C 3H 6-NO-O 2 irradiated mixtures have been tested at 25°C These mixtures initially contained about 16 mTorr C 3H 6, 8 mTorr NO, 0.012 mTorr NO 2, additive and enough O 2 to bring the total pressure to 100 Torr. The NO 2 pressure was monitored photometrically. In the absence of additive, the NO 2 pressure first increases with irradiation time reaching a maximum conversion at about 12 min. As the irradiation time increases beyond 12 min, the NO 2 pressure drops. Ten-min irradiations were done with various amounts of diethylhydroxylamine ((C 2H 5) 2NOH), N-methylamline (C 6H 5NHCH 3), triethylamine ((C 2H 5) 3N), diethylamine ((C 2H 5) 2NH), ethylamine (C 2H 5NH 2), and ammonia (NH 3) added. The NO 2 pressure was reduced to one-half its value in the absence of inhibitor with 1.5 mTorr N-methylaniline, 2.5 mTorr (C 2H 5) 2NOH, 6 mTorr (C 2H 5) 3N or 6.0 mTorr (C 2H 5) 2NH added. Ammonia showed no inhibition, and C 2H 5NH 2 gave slight inhibition. Studies of the per cent conversion of NO to NO 2 vs irradiation time were done with either 8.1 mTorr (C 2H 5) 3N, 6.0 mTorr (C 2H 5) 2NH, 2.2 mTorr (C 2H 5) 2NOH, and 2.4 mTorr N-methylaniline added. The times for maximum per cent conversion of NO to NO 2 were shifted from the additive absent value of 12 min to 15, 18, 22 and 22 min, respectively. In addition the per cent conversion at the maximum was also slightly suppressed with additive present. There is a dark reaction between (C 2H 5) 2NOH and NO 2 which follows the rate law −d[NO 2] dt = k[NO 2][(C 2H 5) 2NOH] . The rate coefficient k = 4.5 × 10 −18 cm 3 s −1 at 25°C is too small for the dark reaction to significantly influence the photochemical inhibition studies.

Photochemical inhibition in cryogenic reaction systems

If diffusion is slow or non-existent in a photochemical system where a large fraction of the incident light is absorbed and reaction is continued to high precentage conversion, account must be taken of both light intensity and consequent concentration gradients when deriving an expression for the rate of photolysis. It is shown how this can be done, in the absence of diffusion, for a parallel-sided film when allowance is made for reactant depletion and competitive light absorption by product species. A digital computer was used to compute product yield-irradiation time curves from the integrated forms of the appropriate rate equations and application of the method to the solid state photolysis of HI is discussed.