Effective Quantum Yield Of Photosystem Research Articles

Trap closure and prey retention in Venus flytrap (Dionaea muscipula) temporarily reduces photosynthesis and stimulates respiration.

The carnivorous plant Venus flytrap (Dionaea muscipula) produces a rosette of leaves: each leaf is divided into a lower part called the lamina and an upper part, the trap, with sensory trigger hairs on the adaxial surface. The trap catches prey by very rapid closure, within a fraction of a second of the trigger hairs being touched twice. Generation of action potentials plays an important role in closure. Because electrical signals are involved in reduction of the photosynthetic rate in different plant species, we hypothesized that trap closure and subsequent movement of prey in the trap will result in transient downregulation of photosynthesis, thus representing the energetic costs of carnivory associated with an active trapping mechanism, which has not been previously described. Traps were enclosed in a gas exchange cuvette and the trigger hairs irritated with thin wire, thus simulating insect capture and retention. Respiration rate was measured in darkness (RD). In the light, net photosynthetic rate (AN), stomatal conductance (gs) and intercellular CO2 concentration (ci) were measured, combined with chlorophyll fluorescence imaging. Responses were monitored in the lamina and trap separately. Irritation of trigger hairs resulted in decreased AN and increased RD, not only immediately after trap closure but also during the subsequent period when prey retention was simulated in the closed trap. Stomatal conductance remained stable, indicating no stomatal limitation of AN, so ci increased. At the same time, the effective quantum yield of photosystem II (PSII) decreased transiently. The response was confined mainly to the digestive zone of the trap and was not observed in the lamina. Stopping mechanical irritation resulted in recovery of AN, RD and PSII. We put forward the first experimental evidence for energetic demands and carbon costs during insect trapping and retention in carnivorous plants, providing a new insight into the cost/benefit model of carnivory.

Photosynthetic acclimation is important for post-submergence recovery of photosynthesis and growth in two riparian species.

Concomitant increases in O(2) and irradiance upon de-submergence can cause photoinhibition and photo-oxidative damage to the photosynthetic apparatus of plants. As energy and carbohydrate supply from photosynthesis is needed for growth, it was hypothesized that post-submergence growth recovery may require efficient photosynthetic acclimation to increased O(2) and irradiance to minimize photo-oxidative damage. The hypothesis was tested in two flood-tolerant species: a C(3) herb, Alternanthera philoxeroides; and a C(4) grass, Hemarthria altissima. The impact of low O(2) and low light, typical conditions in turbid floodwater, on post-submergence recovery was assessed by different flooding treatments combined with shading. Experiments were conducted during 30 d of flooding (waterlogging or submergence) with or without shading and subsequent recovery of 20 d under growth conditions. Changes in dry mass, number of branches/tillers, and length of the longest internodes and main stems were recorded to characterize growth responses. Photosynthetic parameters (photosystem II efficiency and non-photochemical quenching) were determined in mature leaves based on chlorophyll a fluorescence measurements. In both species growth and photosynthesis recovered after the end of the submergence treatment, with recovery of photosynthesis (starting shortly after de-submergence) preceding recovery of growth (pronounced on days 40-50). The effective quantum yield of photosystem II and non-photochemical quenching were diminished during submergence but rapidly increased upon de-submergence. Similar changes were found in all shaded plants, with or without flooding. Submerged plants did not suffer from photoinhibition throughout the recovery period although their growth recovery was retarded. After sudden de-submergence the C(3) plant A. philoxeroides and the C(4) plant H. altissima were both able to maintain the functionality of the photosynthetic apparatus through rapid acclimation to changing O(2) and light conditions. The ability for photosynthetic acclimation may be essential for adaptation to wetland habitats in which water levels fluctuate.

Pre-symptomatic detection of Plasmopara viticola infection in grapevine leaves using chlorophyll fluorescence imaging

Plasmopara viticola is an economically important pathogen of grapevine. Early detection of P. viticola infection can lead to improved fungicide treatment. Our study aimed to determine whether chlorophyll fluorescence (Chl-F) imaging can be used to reveal early stages of P. viticola infection under conditions similar to those occurring in commercial vineyards. Maximum (FV/FM) and effective quantum yield of photosystem II (ΦPSII) were identified as the most sensitive reporters of the infection. Heterogeneous distribution of FV/FM and ΦPSII in artificially inoculated leaves was associated with the presence of the developing mycelium 3 days before the occurrence of visible symptoms and 5 days before the release of spores. Significant changes of FV/FM and ΦPSII were spatially coincident with localised spots of inoculation across the leaf lamina. Reduction of FV/FM was restricted to the leaf area that later yielded sporulation, while the area with significantly lower ΦPSII was larger and probably reflected the leaf parts in which photosynthesis was impaired. Our results indicate that Chl-F can be used for the early detection of P. viticola infection. Because P. viticola does not expand systemically in the host tissues and the effects of infection are localised, Chl-F imaging at high resolution is necessary to reveal the disease in the field.

Leaf plasticity in peanut ( Arachis hypogaea L.) in response to heavy metal stress

Phenotypic plasticity in morphological, anatomical and physiological traits of peanut ( Arachis hypogaea L.) leaves was tested at four different concentrations of Cd, Cu and Zn under greenhouse conditions. Among 18 characteristics tested, nine were found to be the most sensitive and demonstrate the greatest phenotypic plasticity. These were: the leaf area (LA), the leaf mass per area (LMA), chlorophyll a concentration (Chl a), chlorophyll b concentration (Chl b), total chlorophyll concentration (Chl t), the effective quantum yield of photosystem II (ΦPS II), stomatal density of upper epidermis (SDU), palisade thickness (PT), and palisade to spongy thickness ratio (P/S). The plasticity of chlorophyll concentration and fluorescence parameters may be maladaptive and reflects metal toxicity to leaves, whereas the anatomical plasticity is adaptive, indicative of a tradeoff between the physiological and anatomic plasticity. The anatomical plasticity resulted in a xerophyte feature of leaves (i.e. small leaflets, thick lamina, upper epidermis, palisade mesophyll, as well as abundant and small stomata), which enhanced the capacity to resist drought caused by heavy metals via a decrease in root growth.

Diurnal changes in chlorophyll fluorescence and light utilization in Colocasia esculenta leaves grown in marshy waterlogged area

Diurnal cycle of chlorophyll fluorescence parameters was done in Colocasia esculenta L. (swamp taro) grown in marshy land under sun or under shade. The sun leaves maintained higher electron transport rate (ETR) and steady state to initial fluorescence ratio (Fs/F0) than shade leaves. In spite of lower ETR, higher photochemical quenching (PQ), and effective quantum yield of photosystem 2 (ΦPS2) was evident in shade plants compared to plants exposed to higher irradiance. ETR increased linearly with increase in irradiance more under low irradiance (r2 = 0.84) compared to higher irradiance (r2 = 0.62). The maximum quantum yield of PS 2 (Fv/Fm) did not differ much in sun and shade leaves with the exception of midday when excess of light energy absorbed by plants under sun was thermally dissipated. Hence swamp taro plants adopted different strategies to utilize radiation under different irradiances. At higher irradiance, there was faster decline in proportion of open PS 2 centers (PQ) and excess light energy was dissipated through non-photochemical quenching (NPQ). Under shade, absorbed energy was effectively utilized resulting in higher ΦPS2.

Photosynthetic responses to chromosome doubling in relation to leaf anatomy in Lonicera japonica subjected to water stress.

Gas exchange, chlorophyll fluorescence, and contents of some metabolites in two Japanese honeysuckle (Lonicera japonica Thunb.) cultivars, Damaohua (2n = 2x) and Jiufengyihao (2n = 4x), were compared with explore the function of chromosome doubling under water stress conditions. Water stress significantly decreased net photosynthesis rate, stomatal conductance, and transpiration rate of both cultivars. It also decreased electron transport rate, effective quantum yield of Photosystem II, photochemical quenching, and starch content, but increased non-photochemical quenching and contents of total soluble sugars, proline, and malondialdehyde. However, the tetraploid cultivar showed higher resistance to water stress than the diploid, as indicated by the fact that gas exchange, chlorophyll fluorescence, and metabolites were less affected for the tetraploid than the diploid. Moreover, the tetraploid recovered more quickly than the diploid after re-watering. Morphological and anatomical analysis further revealed that the tetraploid possessed less whole plant leaf area, higher leaf mass per unit area, thicker epidermis (both upper and lower) and palisade tissue, as well as denser pubescence. All of those specialised structures caused by chromosome doubling might lead to greater capacity in coping with drought stress. Our findings suggest that the effect of chromosome doubling on drought resistance in L. japonica could attribute to the improvement of structure and photosynthesis-related traits.

Ethylene insensitivity impedes a subset of responses to phosphorus deficiency in tomato and petunia

The role of ethylene in growth and developmental responses to low phosphorus stress was evaluated using ethylene-insensitive 'Never-ripe' (Nr) tomato and etr1 petunia plants. Low phosphorus increased adventitious root formation in 'Pearson' (wild-type) tomato plants, but not in Nr, supporting a role for ethylene in adventitious root development and showing that ethylene is important for this aspect of phosphorus response. Low phosphorus reduced ethylene production by adventitious roots of both genotypes, suggesting that ethylene perception--not production--regulates carbon allocation to adventitious roots at the expense of other roots under low phosphorus stress. With the exception of its effect on adventitious rooting, Nr had positive effects on growth and biomass accumulation in tomato whereas etr1 tended to have negative effects on petunia. This was particularly evident during the recovery from transplanting, when the effective quantum yield of photosystem II of etr1 petunia grown with low phosphorus was significantly lower than 'Mitchell Diploid', suggesting that etr1 petunia plants may undergo more severe post-transplant stress at low phosphorus availability. Our results demonstrate that ethylene mediates adventitious root formation in response to phosphorus stress and plays an important role for quick recovery of plants exposed to multiple environmental stresses, i.e. transplanting and low phosphorus.

Effect of Sequential Isoproturon Pulse Exposure on Scenedesmus vacuolatus

Aquatic organisms are typically exposed to fluctuating concentrations of herbicides in streams. To assess the effects on algae of repeated peak exposure to the herbicide isoproturon, we subjected the alga Scenedesmus vacuolatus to two sequential pulse exposure scenarios. Effects on growth and on the inhibition of the effective quantum yield of photosystem II (PSII) were measured. In the first scenario, algae were exposed to short, 5-h pulses at high isoproturon concentrations (400 and 1000 microg/l), each followed by a recovery period of 18 h, while the second scenario consisted of 22.5-h pulses at lower concentrations (60 and 120 microg/l), alternating with short recovery periods (1.5 h). In addition, any changes in the sensitivity of the algae to isoproturon following sequential pulses were examined by determining the growth rate-EC(50) prior to and following exposure. In both exposure scenarios, we found that algal growth and its effective quantum yield were systematically inhibited during the exposures and that these effects were reversible. Sequential pulses to isoproturon could be considered a sequence of independent events. Nevertheless, a consequence of inhibited growth during the repeated exposures is the cumulative decrease in biomass production. Furthermore, in the second scenario, when the sequence of long pulses began to approach a scenario of continuous exposure, a slight increase in the tolerance of the algae to isoproturon was observed. These findings indicated that sequential pulses do affect algae during each pulse exposure, even if algae recover between the exposures. These observations could support an improved risk assessment of fluctuating exposures to reversibly acting herbicides.

Seasonal variation in the photo-physiology of homogeneous and heterogeneous Symbiodinium consortia in two scleractinian corals

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 361:139-150 (2008) - DOI: https://doi.org/10.3354/meps07360 Seasonal variation in the photo-physiology of homogeneous and heterogeneous Symbiodinium consortia in two scleractinian corals K. E. Ulstrup1,2,4,*, R. Hill1, M. J. H. van Oppen2, A. W. D. Larkum3, P. J. Ralph1 1Institute for Water & Environmental Resource Management, Department of Environmental Science, University of Technology, Sydney, PO Box 123, Broadway, New South Wales 2007, Australia 2Australian Institute of Marine Science, PMB No. 3, Townsville MC, Queensland 4810, Australia 3School of Biological Sciences (A08), University of Sydney, New South Wales 2006, Australia 4Present address: Marine Biological Laboratory, Department of Biology, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark *Email: kulstrup@bi.ku.dk ABSTRACT: Seasonal variation in the composition of the algal endosymbiont community and photo-physiology was determined in the corals Pocillopora damicornis, which show high local fidelity to one symbiont type (Symbiodinium C1), and Acropora valida, with a mixed Symbiodinium symbiont community, comprising members of both clades A and C. The relative abundances of Symbiodinium types varied over time. A significant decline in symbiont densities in both coral species during the summer of 2005 coincided with a NOAA ‘hotspot’ warning for Heron Island. This also coincided with a relative increase in the presence and dominance of clade A in A. valida, particularly in sun-adapted surfaces. The effective quantum yield of Photosystem II (ΦPSII) suggested that sun-adapted surfaces of P. damicornis are more sensitive than shade-adapted surfaces to combined effects of higher temperature and irradiance in summer. Xanthophyll cycling was greater in P. damicornis than A. valida, irrespective of branch position and sampling time; this may be a mechanism by which P. damicornis compensates for its fidelity to Symbiodinium C1. Furthermore, xanthophyll de-epoxidation in P. damicornis symbionts was greater in sun-adapted than shade-adapted surfaces, correlating with non-photochemical quenching (NPQRLC). No variation was found in A. valida, indicating that resident symbiont communities may not have been physiologically compromised, perhaps as a result of changes in the composition of the Symbiodinium community consortia. KEY WORDS: Fast fluorescence kinetics · ITS1 rDNA · LSU rDNA · Symbiodinium · Symbiont density Full text in pdf format PreviousNextCite this article as: Ulstrup KE, Hill R, van Oppen MJH, Larkum AWD, Ralph PJ (2008) Seasonal variation in the photo-physiology of homogeneous and heterogeneous Symbiodinium consortia in two scleractinian corals. Mar Ecol Prog Ser 361:139-150. https://doi.org/10.3354/meps07360Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 361. Online publication date: June 09, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Water-water cycle involved in dissipation of excess photon energy in phosphorus deficient rice leaves

The water-water cycle which may be helpful for dissipating the excitation pressure over electron transport chain and minimizing the risk of photoinhibition and photodamage was investigated in rice after 10-d P-deficient treatment. Net photosynthetic rate decreased under P-deficiency, thus the absorption of photon energy exceeded the energy required for CO2 assimilation. A more sensitive response of effective quantum yield of photosystem 2 (ΦPS2) to O2 concentration was observed in plants that suffered P starvation, indicating that more electrons were transported to O2 in the P-deficient leaves. The electron transport rate through photosystem 2 (PS 2) (Jf) was stable, and the fraction of electron transport rate required to sustain CO2 assimilation and photorespiration (Jg/Jf) was significantly decreased accompanied by an increase in the alternative electron transport (Ja/Jf), indicating that a considerable electron amount had been transported to O2 during the water-water cycle in the P-deficient leaves. However, the fraction of electron transport to photorespiration (Jo/Jf) was also increased in the P-deficient leaves and it was less sensitive than that of water-water cycle. Therefore, water-water cycle could serve as an efficient electron sink. The higher non-photochemical fluorescence quenching (qN) in the P-deficient leaves depended on O2 concentration, suggesting that the water-water cycle might also contribute to non-radiative energy dissipation. Hence, the enhanced activity of the water-water cycle is important for protecting photosynthetic apparatus under P-deficiency in rice.

Distribution and salinity tolerance of intertidal mosses from Nova Scotian salt marshes

Five moss species were found in the high intertidal zone of salt marshes in Nova Scotia, eastern Canada. This is the first report of bryophytes from salt marshes from North America. In each of the salt marshes where mosses occurred, one to three moss species occurred in monospecific or mixed species assemblages. Campylium stellatum and Bryum capillare were the most common species, followed by Didymodon rigidulus, Mnium hornum and Amblystegium serpens in decreasing abundance. All mosses were present below the litter line and occurred in association with Juncus arcticus and J. gerardii, although some collections were also made in association with Spartina pectinata and S. patens. The mosses were exposed in situ to seawater of . 20 ppt. In a laboratory experiment, mats of C. stellatum were exposed to a range of salinities (0, 8, 16, 32 ppt); plants survived 24 h of immersion in seawater of 32 ppt followed by four days in which mats were fully saturated with seawater. There was a slight reduction in effective quantum yield of photosystem II (WPSII ) in the 32 ppt treatment relative to 0 and 8 ppt. Following four subsequent days of desiccation, the full-seawater- and 16-ppt-treated plants had significant reduction in quantum yield. This experiment is consistent with field observations and shows considerable physiological tolerance to salinity in salt marsh mosses.

Action potential in Chara cells intensifies spatial patterns of photosynthetic electron flow and non-photochemical quenching in parallel with inhibition of pH banding

Characean cells exposed to illumination arrange plasma-membrane H(+) fluxes and photosynthesis in coordinated spatial patterns. The limited availability of CO(2) in alkaline bands accounts for the lower effective quantum yield of photosystem II (DeltaF/F(m)') in chloroplasts of these bands compared to acidic zones. The effect of electrically triggered action potential on the spatial distribution of photosynthetic parameters (DeltaF/F(m)' and non-photochemical quenching, NPQ) and extracellular pH was studied with fluorescence imaging and pH microelectrodes. In the resting cell at a range of light intensities, the periodic profile of extracellular pH is parallel to the profile of NPQ and antiparallel to that of DeltaF/F(m)'. After triggering the action potential, the pH banding temporarily disappeared, but in contrast, the differences in effective quantum yield and NPQ patterns became more apparent. The transient changes in pH-banding, effective quantum yield and non-photochemical quenching are discussed in relation to alterations in intracellular Ca(2+) and H(+) concentrations during and after the action potential.

Influence of water stress and low irradiance on morphological and physiological characteristics of Picea asperata seedlings

The combined effects of water stress (WS) and low irradiance (LI) on growth, photosynthesis, osmotic adjustment, and lipid peroxidation were studied in dragon spruce (Picea asperata Mast.) seedlings grown under two water treatments (well watered, 100 % of field capacity, and water stressed, 30 % of field capacity) and two irradiances (HI, 100 % of full sunlight and LI, 15 % of full sunlight). WS reduced growth, chlorophyll (Chl) a and b contents, net photosynthetic rate, transpiration rate, stomatal conductance, and effective quantum yield of photosystem 2 (Y) but increased free proline and malondialdehyde contents. LI increased Chl contents and decreased Y, photochemical quenching (qP), and non-photochemical quenching (qN) under both water treatments. Hence the seedlings in the understory were more sensitive to drought than to LI.

Chlorophyll fluorescence parameters of three Mediterranean shrubs in a summer-autumn period in central Portugal

The photosynthetic performance of Cistus crispus, Centaurea africana and Thymus villosus, three shrubs of the Mediterranean-type maquis vegetation of Central Portugal, were studied between July and December 2003 by means of in vivo chlorophyll a fluorescence measurements. In C. africana total leaf decay occurred between August and October, in T. villosus no clear pattern of variation of the basal fluorescence (Fo) was observed, and in C. crispus an increase of this parameter was observed in late autumn. In all species, the limitation to photosynthesis by photoinhibition and the contribution of non-reversible processes to total photoinhibition were more pronounced in the summer than in the autumn. However, a pronounced decrease of the effective quantum yield of photosystem 2 (ΦPS2) was found in late autumn, probably due to a decrease of the carboxylation efficiency of the Calvin-Benson cycle, which was also supported by a parallel decrease of the photochemical quenching coefficient (qP).

Research note: Salinity tolerance of Arctic kelps from Spitsbergen

SUMMARYThe effect of hypo‐ and hypersaline treatments on the effective quantum yield of photosystem II was comparatively studied with a pulse amplitude modulated fluorometer (PAM) in the brown algal speciesAlaria esculenta,Fucus distichus, Laminaria digitata,Laminaria solidungula,Saccharina latissima(formerlyLaminaria saccharina) andSaccorhiza dermatodeacollected in the Arctic Kongsfjorden (Spitsbergen). While the euryhalineF. distichuswas not affected at all by salinities ranging from 5 to 60 psu,A. esculenta, S. latissimaandL. solidungulaexhibited under hyposaline conditions strong loss of pigments (bleaching) or even high mortality reflecting stenohaline features. In contrast to the latter species,L. digitataandS. dermatodeasurvived all salinities, but showed reduced photosynthetic activities at the lowest and highest salt treatments and hence, can be characterized as stenohaline‐euryhaline organisms. The data are discussed in terms of vertical zonation (eulittoral versus sublittoral habitat), in terms of interactive effects with other abiotic factors such as temperature and in terms of the species‐specific acclimation potential.

Characterising nutrient-induced fluorescence transients (NIFTs) in nitrogen-stressed Chlorella emersonii (Chlorophyta)

K. Shelly, T. Higgins, J. Beardall, B. Wood, D. McNaughton and P. Heraud. 2007. Characterising nutrientinduced fluorescence transients (NIFTs) in nitrogen-stressed Chlorella emersonii (Chlorophyta). Phycologia 46: 503–512. DOI: 10.2216/06-55.1Although determining the nutrient status of algae is highly desirable for water quality management, conventional methods for assessing nutrient limitation are confounded by a range of theoretical and practical limitations. The current paper examines the effectiveness of a novel rapid fluorometric technique, based on observations of nutrient-induced transients in chl a fluorescence (NIFTs), in providing accurate measurements of algal nutrient limitation. The progress of N-starvation in batch cultures of the freshwater chlorophyte Chlorella emersonii was followed and the NIFT responses of cells to N-starvation and additions of both NH4+ and NO3− were characterised using a number of techniques including NIFTs, conventional pigment analysis using UV/Visible spectrophotometry and Fourier transform infrared (FT-IR) and Raman spectroscopy. Results showed that the addition of NH4+ and NO3− elicited distinct changes in in vivo chl a fluorescence in N-limited Chlorella cells. The nature of the fluorescence change was dependent on the form of nitrogen supplied, with NH4+ additions producing a more complex effect on fluorescence than NO3− additions. Interestingly, the greatest fluorescence response following NH4+ injection occurred prior to cells becoming extremely N-starved. Despite Chlorella exhibiting many of the characteristic features of N-deficient cells such as lowered capacity for photosynthetic electron transport (rETRmax), reduced Chl a : β–carotene ratios and increased levels of carbohydrate accumulation relative to protein, values for the maximum effective quantum yield of Photosystem II (ΦPSIIe-max) remained high over the course of N-starvation.

Influence of heat shock on chlorophyll fluorescence of white oak (Quercus pubescens Willd.) leaves

Chlorophyll fluorescence parameters of Quercus pubescens Willd. as response to heat shock (HS) by immersing leaves for 5 and 15 min in water of temperatures between 38 and 59 °C were examined. Fluorescence was measured after different periods of recovery (15, 30, 90, 210, and 1 440 min at 24/26 °C night/day temperature and 100 % humidity). The effective quantum yield of photosystem 2 (Y) in control and HS-treated leaves was always measured after previous 15 min irradiation. Under a 5 min HS, Y did not change after using temperatures below 44 °C, was rapidly restored after HS of moderate temperatures (44-48 °C), and progressively decreased and recovered eventually to the initial value after HS of high temperatures (48-52 °C). Y did not recover after HS with temperatures higher than 52 °C. Increase in the duration of HS from 5 to 15 min lead to change of the initial Y at each HS temperature, but the recovery processes were similar to those characteristic after 5 min incubation. The processes of recovery may depend mainly on the specificity of injuries caused by different heat shock temperatures. Thus Q. pubescens is able to preserve and recover the functional potential of its photosynthetic apparatus in response to HS up to 52 °C.

Association of Rubisco activase with chaperonin-60 : a possible mechanism for protecting photosynthesis during heat stress

Previous studies have shown that inhibition of photosynthesis by moderate heat stress is a consequence of Rubisco deactivation, caused in part by the thermal instability of Rubisco activase. This involvement of Rubisco activase was confirmed in heat stress and recovery experiments using transgenic Arabidopsis plants. Compared with wild-type plants, photosynthesis, the effective quantum yield of photosystem II, and Rubisco activation were less thermotolerant and recovered more slowly in transgenic Arabidopsis plants with reduced levels of Rubisco activase. Immunoblots showed that 65% of the Rubisco activase was recovered in the insoluble fraction after heat stress in leaf extracts of transgenic but not wild-type plants, evidence that deactivation of Rubisco was a consequence of thermal denaturation of Rubisco activase. The transgenic Arabidopsis plants used in this study contained a modified form of Rubisco activase that facilitated affinity purification of Rubisco activase and proteins that potentially interact with Rubisco activase during heat stress. Sequence analysis and immunoblotting identified the beta-subunit of chaperonin-60 (cpn60beta), the chloroplast GroEL homologue, as a protein that was bound to Rubisco activase from leaf extracts prepared from heat-stressed, but not control plants. Analysis of the proteins by non-denaturing gel electrophoresis showed that cpn60beta was associated with Rubisco activase in a high molecular mass complex. Immunoblot analysis established that the apparent association of cpn60beta with Rubisco activase was dynamic, increasing with the duration and intensity of the heat stress and decreasing following recovery. Taken together, these data suggest that cpn60beta plays a role in acclimating photosynthesis to heat stress, possibly by protecting Rubisco activase from thermal denaturation.

Effect of UV radiation on growth, chlorophyll fluorescence and fatty acid composition of Phaeodactylum tricornutum and Chaetoceros muelleri (Bacillariophyceae)

Y. Liang, J. Beardall and P. Heraud. 2006. Effect of UV radiation on growth, chlorophyll fluorescence and fatty acid composition of Phaeodactylum tricornutum and Chaetoceros muelleri (Bacillariophyceae). Phycologia 45: 605–615. DOI: 10.2216/04-61.1The effect of UV radiation on growth, the maximal effective quantum yield of photosystem II (Fv/Fm), the photosynthetic parameters α, ETRmax and Ik, and the fatty acid composition of two diatoms, Phaeodactylum tricornutum and Chaetoceros muelleri, were examined in batch cultures. The cultures were grown at 18 ± 1°C with a 16 : 8 light : dark cycle under three different light regimes: photosynthetically active radiation (PAR) only (60 μmol photons · m−2 · s−1); PAR + UVA radiation (UVAR) [PAR (60μmol photons · m−2 · s−1) plus 8.22 Wm−2 UVAR] and PAR + UVAR + UVB radiation (UVBR) [PAR (60 μmol photons · m−2 · s−1) plus 13.73 Wm−2 UVAR plus 1.04 Wm−2 UVBR]. The cell density, the Fv/Fm and α values of P. tricornutum and C. muelleri were all inhibited as a consequence of PAR + UVAR + UVBR exposure during the experimental period; on the other hand, ETRmax and Ik were somewhat enhanced under this exposure regime. The P. tricornutum samples were harvested at midexponential growth phase while C. muelleri samples were withdrawn on Days 6, 8 and 10 for fatty acid analysis. UV radiation induced significant differences in all the major fatty acids of P. tricornutum. The percentages of eicosapentaenoic acid (EPA) and polyunsaturated fatty acids (PUFA) increased while monounsaturated fatty acids (MUFA) decreased in the PAR + UVAR treatment in comparison with the PAR-only and PAR + UVAR + UVBR treatments. On the other hand, all the major fatty acids of C. muelleri varied with harvest stage and UVR. The percentages of MUFA in C. muelleri increased, while EPA and PUFA decreased under PAR + UVAR + UVBR treatment. Our results indicated that PAR + UVAR may promote EPA and PUFA formation in P. tricornutum, whereas PAR + UVAR + UVBR enhanced SFA and MUFA, and suppressed PUFA formation in C. muelleri.

Differential xanthophyll cycling and photochemical activity in symbiotic dinoflagellates in multiple locations of three species of Caribbean coral

Changes in in situ xanthophyll activity were compared in symbiotic dinoflagellates within the reef-building corals, Montastraea faveolata, Montastraea annularis, and Acropora cervicornis over a daily light cycle from morning until dusk on a shallow (4 m) patch reef. Examination of algae collected from the tops and sides of M. faveolata and M. annularis revealed typical inter-conversion of diadinoxanthin and diatoxanthin, with the greatest abundance of diatoxanthin noted by the mid-morning to afternoon, correlating to daily reduction in the effective quantum yield of photosystem II (Δ F / F m′) for the respective colony location. A. cervicornis had the highest proportion of diatoxanthin relative to the total xanthophyll pool, yet it also displayed the least amount of total daily xanthophyll cycling which did not correlate well with patterns of change in Δ F / F m′. For intraspecific comparisons, no significant difference in daily xanthophyll activity was noted between the different locations in each coral species, while differences in Δ F / F m′ were detected. In some cases temporal trends in nonphotochemical quenching (NPQ) of chlorophyll fluorescence did not match patterns in xanthophyll activity when peak xanthophyll cycling tended to lag behind the immediate light intensity measured in the mid-morning at some colony locations. Genetic characterization of symbionts using polymerase chain reaction-denaturing gradient electrophoresis of the rDNA internal transcribed spacer 2 region (ITS2) revealed that M. faveolata and M. annularis hosted the type B1 symbiont at all locations, while the type A3 symbiont was noted throughout A. cervicornis. Results indicate that while xanthophyll cycling appears to be largely a ubiquitous phenomenon in symbiotic dinoflagellates, the degree of cycling can be quite different between coral species at the same depth and that other biochemical pathways for daily photoprotection may predominate some host–symbiont combinations.