Optimal Quantum Yield Research Articles

Heat acclimation of grapevine leaf photosynthesis: mezo- and macroclimatic aspects.

Heat sensitivity of grapevine (Vitis vinifera L. cv. Kékfrankos) photosynthesis was studied in two vineyards (Eger-Kőlyuktető, flat; and Eger-Nagyeged hill, steep slope) with different mesoclimates and water supply conditions in two climatically different years. 2007 was drier and warmer, with higher vapour pressure deficit (VPD) than 2005. Pre-dawn water potential measurements indicated mild water deficit at the steep-sloped vineyard. In July 2005 mild water deficit enhanced the thermostability of grapevine photosynthesis, as reflected in the temperature dependence of optimal quantum yield (Fv/Fm) and in the critical temperature of initial fluorescence (F0Tc). Decreased Fv/Fm and actual quantum yield (ΔF/Fm') was recorded at most temperatures in September at the water-stressed (steep slope) site. This time, F0Tcs were also lower due to early leaf senescence. In September 2007, heat sensitivity of Fv/Fm was similar to 2005, and ΔF/Fm' indicated higher thermostability at both sites, but keeping the consistent difference between the two vineyards. The critical points of steady-state fluorescence (FsTc) were higher by 3-6°C at both vineyards in 2007 than in 2005. Although, in September thermolabile F0 signals were measured at the water-stressed vineyard, the heat sensitivity was not decreased in light adapted state, assumingly as a result of enhanced xanthophyll cycle pigment pool size. The higher xanthophyll pigments pool size (V + A + Z) in 2007 (compared to 2005) at the unstressed (flat) vineyard suggests that high temperature and VPD play a role in changing (V + A + Z)/(chl a + b), and, thus, results in higher thermostability under high light conditions.

EXPOSURE TO SUDDEN LIGHT BURST AFTER PROLONGED DARKNESS—A CASE STUDY ON BENTHIC DIATOMS IN ANTARCTICA

In polar areas, benthic diatoms are regarded to play a major role in supplying energy to the benthic fauna, particularly prior to the release of microalgae from sea ice and the phytoplankton bloom. As phototrophs, benthic polar diatoms have to contend not only with dark polar nights but also with darkness due to sea-ice and snow cover that can prevail in the littoral zone for additional months. Upon sea ice break-up the autotrophs are suddenly exposed to high light intensities including ultraviolet radiation. The aim of our study was to mimic a sudden spring-time sea ice break-up, focusing on the ultraviolet part of the solar spectrum. We therefore exposed a semi-natural community of benthic diatoms to light burst after a period of total darkness. We studied the effects of different spectral qualities: photosynthetically active radiation (PAR, 400–700 nm; P treatment), PAR+ UV-A (UV-A 320–400 nm; PA treatment), and PAR+UV-A+UV-B (UV-B 280–320 nm; PAB treatment) on cell number (growth), species composition and optimum quantum yield (Fv/Fm) in 2 separate experiments where diatoms were kept in darkness for 15 and 64 days, respectively. In both experiments, the most frequently (>50%) observed species were Gyrosigma fasciola and G. obscururn. No growth was observed and no resting spores were found. In both experiments, the initial optimum quantum yield of the PSII prior to dark treatment was comparable (Fv/Fm = 0.70). The Fv/Fm was not affected after 15 days dark incubation but a significant decrease in photosynthetic efficiency was observed after 64 days in the dark (Fv/Fm = 0.39). Exposure to different light treatments (P, PA, PAB) immediately after different dark incubation periods showed higher reduction in Fv/Fm (PAB > PA > P) after the longer dark period. Estimated P-E curve parameters showed an efficient light harvesting and photosynthetic conversion capacity (α= 0.20; rETRmax=14) that was significantly reduced after 64 days in the dark (α= 0.06; rETRmax=8). The reduction in these photo-physiological indices (a and rETRmax) after dark incubation was compensated with higher saturating irradiance (Ek), which we suspect to be a mechanism to optimize photochemical processes. But the PSII antenna was relatively light-sensitive because photosynthesis was already photoinhibited at half the photon flux density (≥ 585 μmol photons m–2 s–1) relative to light-adapted (≥ 972 μmol photons m–2 s–1) diatoms. We conclude that the benthic diatoms in our study were able to resume photosynthetic activity after 64 days in darkness and they were able to cope with relatively high intensities of UV radiation compared with their natural habitat.

Temperature response in a shallow-water Mediterranean population of Caulerpa racemosa var. cylindracea (Caulerpales, Chlorophyta), and a possible strategy of season anticipation

Abstract We studied growth and photosynthetic response of a shallow-water population of the invasive alga Caulerpa racemosa var. cylindracea off the Island of Ischia (Gulf of Naples, Italy). The effects of temperature on relative growth rate (RGR), light-saturated photosynthetic rate (Pmax), dark respiration rate (Rd) and optimal quantum yield (Fv/Fm) were assessed for thalli collected in two seasons (early winter and early summer). While temperatures higher than 22°C stressed early winter thalli, as reflected in the decrease in growth rates and optimal quantum yields, both increased with temperature in early summer plants. A difference between the two seasonal samples also occurred in the high-temperature sensitivity of respiration rates, which was enhanced in early winter plants. As changes in a number of the traits considered occur in advance of seasonal minima and maxima, C. racemosa var. cylindracea may behave as a season anticipator. The contribution of observed patterns to the colonization success of the alga is discussed.

Susceptibility of spores of different ploidy levels from Antarctic Gigartina skottsbergii (Gigartinales, Rhodophyta) to ultraviolet radiation

M.Y. Roleda, K. Zacher, A. Wulff, D. Hanelt and C. Wiencke. 2008. Susceptibility of spores of different ploidy levels from Antarctic Gigartina skottsbergii (Gigartinales, Rhodophyta) to ultraviolet radiation. Phycologia 47: 361–370. DOI: 10.2216/07-84.1Haploid tetraspores and diploid carpospores from Antarctic Gigartina skottsbergii were exposed in the laboratory to photosynthetically active radiation (400–700 nm = P), P + ultraviolet (UV)-A radiation (320–700 nm = PA) and P + UV-A + UV-B radiation (280–700 nm = PAB). Photosynthetic performance, DNA damage and repair, spore mortality, and an initial characterization of the UV-absorbing mycosporine-like amino acids (MAAs) were studied. Rapid photosynthesis vs irradiance (E) curves of freshly released spores showed that both tetraspores and carpospores were low-light adapted (Ek = 44 ± 2 and 54 ± 2 µmol photons m−2 s−1, respectively). The light-harvesting and photosynthetic conversion efficiencies were similar (α = 0.13), whereas photosynthetic capacity in terms of optimum quantum yield (Fv/Fm) and relative electron transport rate (rETRmax) were significantly higher in carpospores. Photoinhibition and recovery of photosynthesis were not significantly different between spore ploidy but were significantly affected by radiation and exposure time treatments. Accumulation of DNA damage was UV-B dose dependent and significantly higher in tetraspores than in carpospores. After 2 days postcultivation, DNA lesions were completely repaired in spores exposed to UV-B dose less than 1.2 × 104 J m−2. The dynamic recovery of photosynthetic capacity as well as effective DNA repair mechanism contributed to the relatively low spore mortality (4–14%). A substantial amount of UV-screening MAAs shinorine and palythine were observed for the first time in spores of Gigartinales. This study on stress and physiological characterization of seaweed propagules is important to understand recruitment dynamics and life history phase dominance in the field.

Transient sediment load on blades of Arctic Saccharina latissima can mitigate UV radiation effect on photosynthesis

We studied the short-term impact of sediment load on the photosynthetic performance of Saccharina latissima sporophytes exposed to ultraviolet radiation (UVR). The algae were collected from different sediment-influenced environments in Svalbard in August 2007. Initial optimum quantum yield (Fv/Fm) of sediment-covered sporophytes was significantly higher compared to sediment-free sporophytes. Experimental sediment coating on blade discs had a photoprotective function by screening out 92% of the weighted UV-B (UVery) treatment. No UVR-induced photoinhibition was observed in sediment-coated blade discs while sediment removal caused a reduction in Fv/Fm not only after 12-h UVR exposure but also after 6-h recovery in low white light compared to the initial value. Thus, sediment coating has a short-term functional significance in mitigating the negative effect of UVR on photosynthesis of an important kelp species and set a baseline for further studies.

Photoinhibition and photosynthetic pigment reorganisation dynamics in light/darkness cycles as photoprotective mechanisms of <em>Porphyra umbilicalis</em> against damaging effects of UV radiation

Porphyra umbilicalis L. Kutzing collected from the upper intertidal zone at Helgoland, North Sea, was exposed to different spectral ranges of UV radiation under both 12/12 h light/dark cycles and continuous irradiation. In light/dark cycles, oscillations of the optimal quantum yield (Fv /Fm) were observed during the experiments, reaching maximal values at the end of the light phase followed by lower values during the dark phase. Decreased Fv /Fm was observed in thalli illuminated with photosynthetic active radiation (PAR) plus UV-A and PAR+UV-A+UV-B, compared with the PAR control, indicating a certain degree of UV-induced photoinhibition. In addition, a decrease in the percentage of change of the linear initial slope and maximum electron transport rate (ETR) estimated from ETR vs. irradiance curves was induced by UV radiation during the light phase. Recovery during the 12 h dark phase was almost completed in UV-A treated plants. PAR+UV-A seemed not to affect the photosynthesis, measured as O2 production. However, a decrease in O2 production was observed in the PAR+UV-A+UV-B treatment, but it recovered to initial values after 48 h of culture. No changes in total content of photosynthetic pigments were observed. However, thallus absorptance and the in vivo absorption cross-section in the PAR range (400-700 nm) normalised to Chl a (a* parameter) fluctuated during light/dark cycles and were positively correlated with changes in the optimum quantum yield, thus indicating that daily pigment reorganisation in the light-harvesting complex may play a key role in the photosynthetic performance of the algae. Both UV-A and UV-B treatments under continuous irradiation induced a significant reduction in the optimal quantum yield, ETR efficiency and photosynthetic oxygen production during the first 36 h to values around 30% of the initial ones. Thus, different protective mechanisms against UV stress can be observed in P. umbilicalis: dynamic photoinhibition when UVA is combined with PAR, followed by full recovery of photosynthesis during the dark phase, and a more pronounced photoinhibition under UV-B, with only partial recovery after longer time periods, in which photosynthetic pigment reorganisation plays an important role.

Development of an Efficient Photocatalytic System for CO2 Reduction Using Rhenium(I) Complexes Based on Mechanistic Studies

The reaction mechanism of photocatalytic CO2 reduction using rhenium(I) complexes has been investigated by means of a detailed comparison of the photocatalyses of three rhenium(I) complexes, fac-[Re(bpy)(CO)3L] (L = SCN- (1-NCS), Cl- (1-Cl), and CN- (1-CN)). The corresponding one-electron-reduced species (OER) of the complexes play two important roles in the reaction: (a) capturing CO2 after loss of the monodentate ligand (L) and (b) donation of the second electron to CO2 by another OER without loss of L. In the case of 1-NCS, the corresponding OER has both of the capabilities in the photocatalytic reaction, resulting in more efficient CO formation (with a quantum yield of 0.30) than that of 1-Cl (quantum yield of 0.16), for which OER species have too short a lifetime to accumulate during the photocatalytic reaction. On the other hand, 1-CN showed no photocatalytic ability, because the corresponding OER species does not dissociate the CN- ligand. Based on this mechanistic information, the most efficient photocatalytic system was successfully developed using a mixed system with fac-[Re(bpy)(CO)3(CH3CN)]+ and fac-[Re{4,4'-(MeO)2bpy}(CO)3{P(OEt)3}]+, for which the optimized quantum yield for CO formation was 0.59.

Soil temperature and intermittent frost modulate the rate of recovery of photosynthesis in Scots pine under simulated spring conditions

An earlier onset of photosynthesis in spring for boreal forest trees is predicted as the climate warms, yet the importance of soil vs air temperatures for spring recovery remains to be determined. Effects of various soil- and air-temperature conditions on spring recovery of photosynthesis in Scots pine (Pinus sylvestris) seedlings were assessed under controlled environmental conditions. Using winter-acclimated seedlings, photosynthetic responses were followed after transfer to different simulated spring conditions. Recovery rates for photosynthetic electron transport and net CO(2) uptake were slower in plants from cold or frozen soil compared with controls. In addition, a greater fraction of light absorbed was not used photochemically, but was dissipated thermally via xanthophyll cycle pigments. Intermittent frost events decreased photosynthetic capacity and increased thermal energy dissipation. Within a few days after frost events, photosynthetic capacity recovered to prefrost levels. After 18 d under spring conditions, no difference in the optimum quantum yield of photosynthesis was observed between seedlings that had been exposed to intermittent frost and control plants. These results show that, if air temperatures remain favourable and spells of subfreezing air temperatures are only of short duration, intermittent frost events delay but do not severely inhibit photosynthetic recovery in evergreen conifers during spring. Cold and/or frozen soils exert much stronger inhibitory effects on the recovery process, but they do not totally inhibit it.

Photosynthetic performance, DNA damage and repair in gametes of the endemic Antarctic brown alga Ascoseira mirabilis exposed to ultraviolet radiation

Abstract Stress physiology on the reproductive cells of Antarctic macroalgae remained unstudied. Ascoseira mirabilis is endemic to the Antarctic region, an isolated ecosystem exposed to extreme environmental conditions. Moreover, stratospheric ozone depletion leads to increasing ultraviolet radiation (280–400 nm) at the earth's surface, thus it is necessary to investigate the capacity of reproductive cells to cope with different UV irradiances. This study is aimed to investigate the impact of exposure to different spectral irradiance on the photosynthetic performance, DNA damage and gamete morphology of the A. mirabilis. Gametangia, gametes and zygotes of the upper sublittoral brown alga A. mirabilis were exposed to photosynthetically active radiation (PAR = P; 400–700 nm), P + UV‐A radiation (UV‐A, 320–400 nm) and P + UV‐A + UV‐B radiation (UV‐B, 280–320 nm). Rapid photosynthesis versus irradiance curves of freshly released propagules were measured. Photosynthetic efficiencies and DNA damage (in terms of cyclobutane pyrimidine dimers) were determined after 1, 2, 4 and 8 h exposure as well as after 2 days of recovery in dim white light. Saturation irradiance (Ik) in freshly released propagules was 52 μmol photons m−2 s−1. Exposure for 1 h under 22 μmol photons m−2 s−1 of PAR significantly reduced the optimum quantum yield (Fv/Fm), suggesting that propagules are low light adapted. Furthermore, UVR significantly contributed to the photoinhibition of photosynthesis. Increasing dose as a function of exposure time additionally exacerbated the effects of different light treatments. The amount of DNA damage increased with the UV‐B dose but an efficient repair mechanism was observed in gametes pre‐exposed to a dose lower than 5.8 × 103 J m−2 of UV‐B. The results of this study demonstrate the negative impact of UV‐B radiation. However, gametes of A. mirabilis are capable of photosynthetic recovery and DNA repair when the stress factor is removed. This capacity was observed to be dependent on the fitness of the parental sporophyte.

Responses of photosynthetic activity in the drought-tolerant cyanobacterium, Nostoc flagelliforme to rehydration at different temperature

Photosynthetic activity during rehydration at four temperatures (5, 15, 25, 35 °C) was studied in a terrestrial, highly drought-tolerant cyanobacterium, Nostoc flagelliforme. At all the temperatures, the optimum quantum yield F v/ F m increased rapidly within 1 h and then increased slowly during the process of rehydration. The increase in F v/ F m at 25 and 35 °C was larger than that at 5 and 15 °C. In addition, the changes of initial intensity of fluorescence ( F 0) and variable fluorescence ( F v) were more significant at 25 and 35 °C than those at 5 and 15 °C. Chlorophyll a content increased with the increase of temperature during the course of rehydration, with this being more pronounced at 25 and 35 °C. The photosynthetic rates at 25 and 35 °C were higher than those at 5 and 15 °C. Induction of chlorophyll fluorescence with sustained rewetting at 5 and 15 °C had two phases of transformation, whereas at 25 and 35 °C it had a third peak kinetic phase and showed typical chlorophyll fluorescence steps on rewetting for 24 h, representing a normal physiological state. A comparison of the chlorophyll fluorescence parameters, chlorophyll a content, and the chlorophyll fluorescence induction led to the conclusion that N. flagelliforme had a more rapid and complete recovery at 25 and 35 °C than that at 5 and 15 °C, although it could recover its photosynthetic activity at any of the four temperatures.

Response of post-storage carbohydrate levels in pelargonium cuttings to reduced air temperature during rooting and the relationship with leaf senescence and adventitious root formation

Rooting of dark-stored pelargonium ( Pelargonium × hortorum) cuttings can be restricted by carbohydrate shortage resulting from the interplay between depleted carbohydrate reserves and weak photosynthesis under the low light conditions of winter in Central Europe. The hypothesis was tested, that considerably reduced air temperature during rooting increases current availability of carbohydrates, thereby improving survival and root formation. Dark-stored cuttings (4 days, 10 °C) of storage-tolerant and -sensitive pelargonium cultivars, ‘Isabell’ and ‘Telemann’, respectively, were rooted in climate chambers (PPFD: 100 μmol m −2 s −1 per 10 h day-length) at reduced air temperature (10 °C, root zone temperature: 20 °C) and compared with those grown at 20 °C (air and root zone). Carbohydrate levels in different cutting tissues were analysed during the rooting period and related to leaf performance and root formation. In addition, net photosynthetic CO 2 gas exchange at ambient temperatures (10 °C versus 20 °C, PPFD: 100 μmol m −2 s −1) and leaf chlorophyll fluorescence (CF) parameters at 20 °C of oldest leaves were determined. With both cultivars, lower air temperature significantly increased tissue carbohydrate levels, particularly sugars. This was associated with higher net photosynthetic rates in the light and increased accumulation of shoot dry matter. ‘Telemann’ cuttings showed a lower optimum quantum yield of PSII ( F v/ F m) during the early rooting period when compared to ‘Isabell’, and thereafter responded to the low air temperature with an increase in non-photochemical quenching ( q N). Higher sugar levels during rooting, mediated by low air temperature were positively correlated with reduced leaf senescence, higher survival rate and higher number of roots. Strongest correlations were found with sucrose, particularly for the cultivar ‘Telemann’. It is concluded that increased sugar levels were causally involved in repressed leaf senescence and contributed to improved root formation in basal stems exposed to high temperature. The results provide new prospects for the control of air temperature during rooting of cuttings that exhibit low current photosynthesis.

Development of a Quantitative Bio/Chemiluminescence Spectrometer Determining Quantum Yields: Re‐examination of the Aqueous Luminol Chemiluminescence Standard

We have developed a bio/chemiluminescence spectrometer with a cooled charge-coupled-device (CCD) detector to obtain a quantitative luminescence spectrum as the absolute number of all emitted photons at each wavelength. The integrated area of the spectrum divided by the number of reacted substrate molecules gives the quantum yield. Calibration of the absolute sensitivity of the CCD-spectrometer system was performed by using lasers and a tungsten lamp with calibrated powers as primary light standards, and calibration of the light-collection efficiency of the spectrometer with several kinds of cells for liquid samples was achieved by introducing a simple reference double-plate cell. The reference cell is not convenient for final bio/chemiluminescence measurements but is useful for the calibration because it has well-defined angular dependence of light emission, allowing accurate calculation of the light-collection efficiency. Using this CCD-spectrometer system, we re-examined the quantum yield of aqueous luminol chemiluminescence with H2O2 catalyzed by horseradish peroxidase. The quantum yield was constant for a wide range of luminol concentrations, whereas it changed and had an optimum against H2O2 concentrations. The optimum quantum yield was 1.23(+/-0.20)%, which is in good agreement with previously reported values.

Cultivation of the brown alga Hizikia fusiformis (Harvey) Okamura: stress resistance of artificially raised young seedlings revealed by chlorophyll fluorescence measurement

Commercial farming of the intertidal brown alga Hizikia fusiformis (Harvey) Okamura in China and South Korea in the sea depends on three sources of seedlings: holdfast-derived regenerated seedlings, young plants from wild population and zygote-derived seedlings. Like many successfully farmed seaweed species, the sustainable development of Hizikia farming will rely on a stable supply of artificial seedlings via sexual reproduction under controlled conditions. However, the high rate of detachment of seedlings after transfer to open sea is one of the main obstacles, and has limited large-scale application of zygote-derived seedlings. To seek the optimal condition for growing seedlings on substratum in land-based tanks for avoidance of detachment in this investigation, young seedlings were grown in both outdoor tanks exposed directly to sunlight and in indoor raceway tanks in reduced, filtered sunlight. Results showed that young seedlings, immediately after fertilization, could withstand a daily fluctuation of direct solar irradiance up to a level of 1800 mu mol photons m(-1)s(-1), and maintained a faster growth rate than seedlings grown in indoor tanks. Detailed experiments by use of chlorophyll fluorescence measurements further demonstrated that the overnight (12 h) recovery of optimal fluorescence quantum yield (F-v/F-m) of seedlings after 1 h treatment at 40 degrees C was 98%, and the 48 h recovery of F-v/F-m of seedlings after 1 h exposure to 1800 mu mol m(-2)s(-1) was 92%. Forty-one-day-old seedlings showed no significant decrease of optimal fluorescence quantum yield at salinity ranging from 30 to 5 ppt for a treatment up to 17 h. Six-hour desiccation treatment did not have any influence on the optimal fluorescence quantum yield. Exposure to 18 mmol L-1 sodium hypochlorite for 10 min did not damage the PSII efficiency, and thus could be used to remove epiphytic algae. The strong tolerance of young seedlings to high temperature, high irradiance, low salinity and desiccation found in this investigation supports the view that mass production of Hizikia seedlings should be performed in ambient light and temperature instead of in shaded greenhouse tanks.

Phytotoxic activity of caulerpenyne from the Mediterranean invasive variety of Caulerpa racemosa: a potential allelochemical

Allelopathy has been postulated as a factor in the colonisation success of Caulerpa racemosa var. cylindracea, an introduced chlorophyte alga which has become invasive in the Mediterranean Sea. In order to reveal their possible phytotoxic activity, secondary metabolites were isolated from a population growing in the Gulf of Naples (Italy) and tested on leaf tissue of the native seagrass Cymodocea nodosa, which often co-occurs with Caulerpa in nature. The seaweed metabolites were identified by 1H and 13C NMR analysis and leaf portions of C. nodosa were exposed to crude diethyl ether extract and purified compounds in the laboratory, under controlled conditions of irradiance and temperature for a period of 144 h. Eventual changes in the photosynthetic performance of the seagrass tissue following the treatment were tested by monitoring its optimal quantum yield with a pulse amplitude modulated (PAM) fluorometer. One of the identified compounds, caulerpenyne, showed a phytotoxic effect, while the other purified metabolites did not reveal any effect at the assayed concentrations. Thus, our results seem to suggest a possible allelopathic activity of caulerpenyne, which may play a role in the successful competition of the invasive C. racemosa var. cylindracea with native macrophytes, such as seagrasses.

UV effects on stoichiometry and PUFAs of Selenastrum capricornutum and their consequences for the grazer Daphnia magna

Summary1. The effect of ultraviolet (UV) radiation (280–400 nm) on fatty acid composition and elemental ratios of carbon (C), nitrogen (N) and phosphorus (P) of a unialgal culture of the chlorophyte Selenastrum capricornutum was investigated. Algae were cultured in the presence or absence of UV radiation and were subsequently fed to Daphnia magna to assess potential effects of UV on zooplankton fatty acid composition, growth and reproduction.2. Algal growth rate was substantially reduced by UV radiation, probably because of a severe inhibition of photosynthetic efficiency (measured as optimal quantum yield).3. Algae exposed to UV radiation had a significantly reduced content of 18 : 1 n‐9, while C18 polyunsaturated fatty acids (PUFAs) were higher under UV radiation. These observations point at an increased demand for and synthesis of PUFAs under UV stress.4. The C : P and N : P ratios showed a remarkable decrease in UV‐exposed cells primarily owing to an increased uptake of P. The nutritional quality in terms of both fatty acid composition and stoichiometry was therefore higher in the UV treatment relative to the control.5. Despite the UV‐induced changes in nutritional quality of S. capricornutum, no significant effects on D. magna growth or reproduction were detected. The fatty acid composition of Daphnia fed on UV irradiated algae showed a significantly lower content of 18 : 1 n‐9, but no changes in the essential PUFAs.

갈조류 양식 모자반(Sargassum fulvellum)과 해적생물에 대한 pH와 염분의 효과

The effects pH and salinity on the brown alga Sargassum fulvellum were investigated in the context of the removal of two major associated animals, Caprella scaura and Gammaropsis utinomi. Optimum quantum yield (Fv/Fm) of S. fulvellum was also examined in the same experimental conditions as an index of stress. Experiments on pH and salinity tolerances of the two animal species indicated that mortality was more than 80% at extremes of pH (2, 3, 4, 10, 11, 12) and salinity (0, 3.5, 7, 10, 44 psu) after a 5 min treatment. Lethal time (LT50) from pH 2 to pH 4 was less than 90 sec in C. scaura, and less than 70 sec in G. utinomi. From 0 to 10 psu, LT50 was less than 20 sec in C. scaura and less than 60 sec in G. utinomi. The quantum yield of S. fulvellum was not significantly different from controls within the pH range 4~10, and within the salinity range of 7-40 psu. When exposed to pH and salinity conditions outside these ranges, the effect of these factors on the removal of two animal species was higher, but quantum yield was highly reduced. These results indicate that the optimal conditions for removing the animal species without affecting optimum quantum yield were pH 4-10, and salinities 7-10 psu and 44 psu.

Effects of changes in ambient PAR and UV radiation on the nutritional quality of an Arctic diatom ( Thalassiosira antarctica var. borealis)

Polyunsaturated fatty acids (PUFAs) are essential macromolecules that are synthesized by phytoplankton during spring bloom, and they play a key role in the Arctic food web. They are, however, considered to be sensitive to oxidation by UV radiation (280–400 nm). Changes in the food quality of primary producers may affect the transport of biomass and energy in the whole ecosystem. Using a common Arctic diatom, we looked at the effect of ambient and increased UV radiation on its nutritional quality, specifically, the fatty acid composition and elemental ratios. In May 2004, in the archipelago of Svalbard (79° N), a unialgal culture of Thalassiosira antarctica var . borealis was subjected to a 17-day experiment in outdoor aquaria. The diatoms were kept in semi-continuous culture (40 1) and exposed to three treatments with different levels of UV radiation: none (UV-shielded), ambient, and enhanced. Fatty acid composition, C:N:P ratios, photosynthetic pigment composition, optimum quantum yield of PSII, and cell numbers were analysed over the experimental period. An initial increase in PAR (photosynthetically active radiation, 400–700 nm) intensities profoundly affected the fatty acid composition and substantially inhibited the synthesis of PUFAs, but the relative amounts of PUFAs were not reduced by UV radiation. Enhanced UV radiation did, however, cause a significant reduction in optimum quantum yield of PSII and affected some fatty acids, mainly 18:0 and 16:1 n-7, during the first week of the experiment. Both ambient and enhanced UV radiation caused significantly lower C:P and N:P ratios. At the same time, these treatments elicited a higher relative content of the photoprotective pigments diadinoxanthin and diatoxanthin. After acclimation to the new light levels these effects faded off. Thus, brief periods with high light exposure may cause significant changes in photosynthetic activity and food quality, but the capacity for photo-acclimation seems high. The impact of UV radiation seems to be less important for food quality than that of PAR during a sudden rise in total light intensity.

Internalization of Near-Infrared Fluorescent Dyes within Isolated Leukocyte Populations

Scientists have expressed continued interest in the development of microsensor technology that can indicate toxicity that occurs within a cell after a chemical challenge. One of the more useful approaches of microsensor technology is the application of fluorescent spectroscopy to indicate early-stage injury with optimal specificity and decreased background interference. If the toxicity is detected during the early onset period of injury, then the probability for therapeutic recovery is promising. There has been increasing interest in the use of infrared (IR) and near infrared (NIR) dyes as biological microsensors due to their fluorescent spectral characteristics. Three of the most essential characteristics are the ability to minimize background interference by extraneous biological matrices, to exhibit optimal molar absorptivity and quantum yields, to maintain chronic cellular homeostasis. Therefore, the present study was developed to determine if selected NIR dyes would distribute within isolated neutrophil populations without altering normal cellular homeostasis using fluorescent wavelength analysis. The results demonstrate that selected NIR dyes undergo internalization within target cell populations while maintaining cell viability and homeostasis. In addition, these dyes demonstrate changes in absorbance and fluorescence analysis after the immune cells were challenged with a stimulant. Moreover, critical cellular functions, such as degranulation and superoxide production were not compromised by the internalization of the NIR dyes. These data suggest that selected NIR dyes can undergo intracellular uptake within neutrophil cultures without altering the normal functional capabilities of the targeted cell population.

Ultrastructure and photosynthesis in the supralittoral green macroalga Prasiola crispa from Spitsbergen (Norway) under UV exposure

A. Holzinger, U. Karsten, C. Lütz and C. Wiencke. 2006. Ultrastructure and photosynthesis in the supralittoral green macroalga Prasiola crispa from Spitsbergen (Norway) under UV exposure. Phycologia 45: 168–177. DOI: 10.2216/05-20.1The effects of mild a.gificial UV conditions (4.7 W m−2 UV-A, 320–400 nm and 0.20 W m−2 UV-B, 280–320 nm) plus PAR (25–30 µmol photons m−2 s−1) at 4–6°C on photosynthesis and ultrastructure of the aeroterrestrial green macroalga Prasiola crispa (Lightfoot) Kützing from the Arctic were investigated. Specimens were collected from an aeroterrestrial rocky cliff in Kongsfjorden (Ny-Ålesund, Spitsbergen, Norway, 78°55.5′N, 11°56.0′E). Exposure for 6 h and 24 h to PAR + UV-A + UV-B led to a decrease in the optimum quantum yield (PS II efficiency, Fv /Fm) to 73.7% and 42.0% of the control value, respectively. In addition, the relative electron transport rate as a function of the photon fluence rate (PI curve) was determined. This showed that the α value declined in concert with Fv /Fm in UV-exposed samples. In parallel to the fluorescence measurements, tissue samples were prepared for transmission electron microscopy. Whereas 6 h of UV treatment did not lead to significant alterations in the ultrastructure compared to control samples, 24 h of UV treatment caused slight defects. Occasionally, thylakoid membranes showed dilatations and the number of plastoglobuli appeared reduced. Formation of a large number of cytoplasmic globules with a diameter in the range of 0.4–0.8 µm and a medium electron-dense contrast was observed. The data presented demonstrate that P. crispa is rather insensitive to experimental UV treatment and thus seems to be well adapted to cope with increased UV irradiation expected to occur as a consequence of decreased stratospheric ozone concentrations in the northern hemisphere.

The role of ammonium in photoprotection against high irradiance in the red alga Grateloupia lanceola

Combined and/or interactive effects of inorganic nitrogen (as ammonium) and irradiance on the accumulation of nitrogenous compounds, like UV-absorbing mycosporine-like amino acids (MAAs), chlorophyll a and phycobiliproteins, were examined in the red alga Grateloupia lanceola (J. Agardh) J. Agardh in a high irradiance laboratory exposure and a subsequent recovery period under low light. Also, photosynthetic activity as in vivo chlorophyll fluorescence of photosystem II, i.e. optimum quantum yield ( F v/ F m), electron transport rate (ETR) and quantum efficiency, were examined. Photosynthetic activity, phycobiliproteins and internal nitrogen content declined during the 3-day PAR (photosynthetically active radiation; 600 μmol s −1 m −2) and PAR + UVR (ultraviolet radiation; UVB 280–315 nm 0.8 W m −2, UVA 315–400 nm 16 W m −2) exposure. Ammonium supplied in the culture medium (0, 100 and 300 μM NH 4Cl) modified the responses of the alga to high irradiance exposures in a concentration dependent manner, mainly with respect to recovery, as the highest recovery during a 10-day low light period was produced under elevated concentration of ammonium (300 μM). The recovery of photosynthetic activity and phycobiliproteins was enhanced in the algae previously incubated under PAR + UVR as compared to exposure to only PAR, suggesting a beneficial effect of UVR on recovery or photoprotective processes under enriched nitrogen conditions. However, the content of MAAs did not follow the same pattern and thus it could not be concluded as the cause of observed enhanced recovery.