Effective Quantum Yield Of Photosystem Research Articles

Dehydration-induced changes in spectral reflectance indices and chlorophyll fluorescence of Antarctic lichens with different thallus color, and intrathalline photobiont

In this study, we investigated responses of the Photochemical Reflectance Index (PRI), and Normalized Difference Vegetation Index (NDVI) to gradual dehydration of several Antarctic lichen species (chlorolichens: Xanthoria elegans, Rhizoplaca melanophthalma, Physconia muscigena, cyanolichen: Leptogium puberulum), and a Nostoc commune colony from fully wet to a dry state. The gradual loss of physiological activity during dehydration was evaluated by chlorophyll fluorescence parameters. The experimental lichen species differed in thallus color, and intrathalline photobiont. In the species that did not exhibit color change with desiccation (X. elegans), NDVI and PRI were more or less constant (mean of 0.25, − 0.36, respectively) throughout a wide range of thallus hydration status showing a linear relation to relative water content (RWC). In contrast, the species with apparent species-specific color change during dehydration exhibited a curvilinear relation of NDVI and PRI to RWC. PRI decreased (R. melanophthalma, L. puberulum), increased (N. commune) or showed a polyphasic response (P. muscigena) with desiccation. Except for X. elegans, a curvilinear relation was found between the NDVI response to RWC in all species indicating the potential of combined ground research and remote sensing spectral data analyses in polar regions dominated by lichen flora. The chlorophyll fluorescence data recorded during dehydration (RWC decreased from 100 to 0%) revealed a polyphasic species-specific response of variable fluorescence measured at steady state—Fs, effective quantum yield of photosystem II (ΦPSII), and non-photochemical quenching (qN). Full hydration caused an inhibition of ΦPSII in N. commune while other species remained unaffected. The dehydration-dependent fall in ΦPSII was species-specific, starting at an RWC range of 22–32%. Critical RWC for ΦPSII was around 5–10%. Desiccation led to a species-specific polyphasic decrease in Fs and an increase in qN indicating the involvement of protective mechanisms in the chloroplastic apparatus of lichen photobionts and N. commune cells. In this study, the spectral reflectance and chlorophyll fluorescence data are discussed in relation to the potential of ecophysiological processes in Antarctic lichens, their resistance to desiccation and survival in Antarctic vegetation oases.

Environmental safety data on CuO and TiO2 nanoparticles for multiple algal species in natural water: Filling the data gaps for risk assessment

Most research on nanoparticle (NP) ecotoxicological effects has been conducted on single species in laboratory conditions that are not environmentally representative. We compared the effects of CuO NPs, CuSO4 (ionic control) and TiO2 NPs in nutrient-adjusted natural water (ANW) and in the OECD201 standard medium to four different algal species: green algae Raphidocelis subcapitata and Chlamydomonas reinhardtii, a diatom Fistulifera pelliculosa, and a cyanobacterium Synechocystis sp. Biomass and the effective quantum yield of photosystem II (Fv/Fm) were used as toxicity endpoints. CuO NPs were very toxic across taxa in the OECD201 assay (biomass-based 72 h EC50 0.2–0.9 mg l−1). Toxicity of CuO NPs was explained by shedding of ions from particles as Cu2+ is highly toxic: 72 h EC50 in the OECD201 medium was 0.01–0.03 mg l−1 in three species and 0.003 mg l−1 in the case of the cyanobacterium. Toxicity of copper compounds was overall reduced in ANW, presumably because of reduced bioavailability due to metal ions binding to natural organic matter. Copper compounds were more toxic to the cyanobacterium than to other algae and this effect was not amended in ANW. TiO2 NPs did not inhibit the biomass production and photosynthesis of the diatom or the cyanobacterium up to 100 mg l−1, but inhibited biomass production of green algae in the OECD201 medium (EC50 14–15 mg l−1). TiO2 NPs also did not significantly inhibit Fv/Fm up to 100 mg l−1, suggesting a general lack of effect on photosynthesis. Adverse effects of TiO2 NPs were at least in part due to cell-NP heteroagglomeration. Our data are informative for the complete risk assessment of engineered NPs by filling data gaps about NP effects in environmentally realistic conditions.

Studies on the ·OH Inactivation of Non-native Aquatic Organisms and Potential Disinfection Byproduct Formation for Oceanic Environmental Safety

This work was carried out based on the principles of biological effectiveness and environmental acceptability of the International Maritime Organization (IMO). The non-native red tide organisms Prorocentrum donghaiense and Scrippsiella trochoidea were selected to examine ·OH inactivation to meet the IMO standard of ballast water discharge (< 10 cells/mL). The effective quantum yield of photosystem II of algal chlorophyll rapidly decreased to zero within a contact time of only 6 s. Under scanning electron microscope (SEM) observation, the algal cells treated with the ·OH inactivation dose still had an intact shape and did not release cellular material, and thus, there are no risks associated with oceanic environmental safety. The potential disinfection byproducts (DBPs) from discharged ship’s ballast water at high salinity (33.7 PSU) treated at a maximum TRO dose of 2.41 mg/L were analyzed by 5-day storage experiments. The results indicated that the contents of bromate, trihalomethanes (THMs), haloacetic acids (HAAs) and haloacetonitriles (HANs) were below the WHO drinking water standards. Therefore, discharged ship’s ballast water with ·OH inactivation is safe for oceanic environments.

Physiological Regulation Associated with Differential Tolerance to Iron Deficiency in Soybean

Iron deficiency has become a yield‐limiting factor in many agricultural areas. This study was conducted to elucidate the relationship between physiological traits and soybean [Glycine max (L.) Merr.] tolerance in the presence of different FeEDTA concentrations. Two hydroponic experiments using prescreened Fe‐efficient (FeE) and Fe‐inefficient (FeI) soybean genotypes were performed in 2014 and 2015, respectively. Various chlorophyll fluorescence parameters, antioxidant enzyme activities, and the dry weight of the plants were determined and analyzed by canonical correlation analysis, stepwise regression, and logistic equation. The effective quantum yield of photosystem II (PSII) (PhiPSII), maximal photochemical efficiency of PSII (Fv/Fm), superoxide dismutase (SOD), and peroxidase (POD) activity of the FeE genotypes were significantly higher than those of the FeI genotypes (P &lt; 0.05). High catalase (CAT) and POD activities could improve photoprotection and PhiPSII under Fe deficiency. High POD and CAT activities and high Fv/Fm are conducive to increasing the chlorophyll content of E genotypes, and high CAT activity and longer ∆t are also conducive to increasing dry matter accumulation in FeE genotypes under Fe deficiency. In particular, in the presence of 0.02 mM FeEDTA, FeE genotypes exhibit higher PhiPSII, electron transport rate (ETR), and Fv/Fm values as well as higher SOD, POD, and CAT activities than FeI genotypes. Moreover, FeE genotypes show greater dry matter accumulation because of the longest ∆t in the presence of 0.02 mM FeEDTA. Thus, FeE genotypes have stronger tolerance to Fe deficiency because of their higher antioxidant, photochemical, and photoprotection abilities as well as their increased dry matter accumulation resulting from their longer ∆t in the presence of 0.02 mM FeEDTA.

Photosynthetic and antioxidant responses of the tropical intertidal seagrasses Halophila ovalis and Thalassia hemprichii to moderate and high irradiances

AbstractThis study investigated photosynthetic and oxidative stress-related responses to moderate (500 μmol photons m−2s−1) and high irradiances (1500 μmol photons m−2s−1) in two tropical intertidal seagrasses,Halophila ovalisandThalassia hemprichii. Exposure to high irradiance for 3 h resulted in a large decline in the maximum quantum yield of photosystem II (Fv/Fm) and in the effective quantum yield of photosystem II (ΦPSII) but induced non-photochemical quenching (NPQ) and chloroplast clumping inH. ovalis.Thalassia hemprichii, however, showed only a minor decrease in Fv/Fm and ΦPSII, and no change in either NPQ or the intracellular arrangement of chloroplasts. The irradiance did not affect reactive oxygen species (ROS) or superoxide dismutase (SOD) activity in either seagrass, whereas high irradiance enhanced ascorbate peroxidase (APX) activity inH. ovalis. The results from a subsequent experiment using an oxidative stress inducer, methyl viologen (MV), also showed a higher degree of Fv/Fm inhibition inH. ovalis. These results show thatH. ovalisis much more physiologically responsive to high irradiances and oxidative stress thanT. hemprichiiand that its photoprotective mechanisms involve NPQ, APX and reduction of the amount of light absorbed through the clumping of its chloroplasts.

Biochemical and Physiological Characteristics of Photosynthesis in Plants of Two Calathea Species.

Plants of the genus Calathea possess many leaf colors, and they are economically important because they are widely used as ornamentals for interior landscaping. Physiological performances and photosynthetic capacities of C. insignis and C. makoyana were investigated. The photosynthetic efficiencies of C. insignis and C. makoyana were significantly increased when the photosynthetic photon flux density (PPFD) increased from 0 to 600 μmol photons·m−2·s−1 and became saturated with a further increase in the PPFD. The two Calathea species had lower values of both the light saturation point and maximal photosynthetic rate, which indicated that they are shade plants. No significant differences in predawn Fv/Fm values (close to 0.8) were observed between dark-green (DG) and light-green (LG) leaf sectors in all tested leaves. However, the effective quantum yield of photosystem II largely decreased as the PPFD increased. An increase in the apparent photosynthetic electron transport rate was observed in both species to a maximum at 600 μmol·m−2·s−1 PPFD, following by a decrease to 1500 μmol·m−2·s−1 PPFD. Compared to LG leaf extracts, DG leaf extracts contained higher levels of chlorophyll (Chl) a, Chl b, Chls a + b, carotenoids (Cars), anthocyanins (Ants), flavonoids (Flas), and polyphenols (PPs) in all plants, except for the Ant, Fla and PP contents of C. insignis plants. Calathea insignis also contained significantly higher levels of total protein than did C. makoyana. The adjusted normalized difference vegetation index (NDVI), photochemical reflectance index (PRI), red-green, and flavonol index (FlavI) were significantly correlated to leaf Chls a + b, Cars, Ants, and Flas in C. makoyana, respectively, and can be used as indicators to characterize the physiology of these plants.

Effect of carbon limitation on photosynthetic electron transport in Nannochloropsis oculata

This study describes the impacts of inorganic carbon limitation on the photosynthetic efficiency and operation of photosynthetic electron transport pathways in the biofuel-candidate microalga Nannochloropsis oculata. Using a combination of highly-controlled cultivation setup (photobioreactor), variable chlorophyll a fluorescence and transient spectroscopy methods (electrochromic shift (ECS) and P700 redox kinetics), we showed that net photosynthesis and effective quantum yield of Photosystem II (PSII) decreased in N. oculata under carbon limitation. This was accompanied by a transient increase in total proton motive force and energy-dependent non-photochemical quenching as well as slightly elevated respiration. On the other hand, under carbon limitation the rapid increase in proton motive force (PMF, estimated from the total ECS signal) was also accompanied by reduced conductivity of ATP synthase to protons (estimated from the rate of ECS decay in dark after actinic illumination). This indicates that the slow operation of ATP synthase results in the transient build-up of PMF, which leads to the activation of fast energy dissipation mechanisms such as energy-dependent non-photochemical quenching. N. oculata also increased content of lipids under carbon limitation, which compensated for reduced NAPDH consumption during decreased CO2 fixation. The integrated knowledge of the underlying energetic regulation of photosynthetic processes attained with a combination of biophysical methods may be used to identify photo-physiological signatures of the onset of carbon limitation in microalgal cultivation systems, as well as to potentially identify microalgal strains that can better acclimate to carbon limitation.

Structural and functional integrity of Sulla carnosa photosynthetic apparatus under iron deficiency conditions.

The abundance of calcareous soils makes bicarbonate-induced iron (Fe) deficiency a major problem for plant growth and crop yield. Therefore, Fe-efficient plants may constitute a solution for use on calcareous soils. We investigated the ability of the forage legume Sulla carnosa (Desf.) to maintain integrity of its photosynthetic apparatus under Fe deficiency conditions. Three treatments were applied: control, direct Fe deficiency and bicarbonate-induced Fe deficiency. At harvest, all organs of deficient plants showed severe growth inhibition, the effect being less pronounced under indirect Fe deficiency. Pigment analysis of fully expanded leaves revealed a reduction in concentrations of chlorophyll a, chlorophyll b and carotenoids under Fe deficiency. Electron transport rate, maximum and effective quantum yield of photosystem II (PSII), photochemical quenching (qP), non-photochemical quenching (qN) as well as P700 activity also decreased significantly in plants exposed to direct Fe deficiency, while qN was not affected. The effects of indirect Fe deficiency on the same parameters were less pronounced in bicarbonate-treated plants. The relative abundances of thylakoid proteins related to PSI (PsaA, Lhca1, Lhca2) and PSII (PsbA, Lhcb1) were also more affected under direct than indirect Fe deficiency. We conclude that S.carnosa can maintain the integrity of its photosynthetic apparatus under bicarbonate-induced Fe deficiency, preventing harmful effects to both photosystems under direct Fe deficiency. This suggests a high capacity of this species not only to take up Fe in the presence of bicarbonate (HCO3- ) but also to preferentially translocate absorbed Fe towards leaves and prevent its inactivation.

Photochemical responses to abrupt and gradual chilling treatments in eucalyptus species

Eucalyptus plant is one of the most economic important forest species explored worldwide and in some countries its cultivation is expanding to regions with lower temperatures, including Brazil. This study aimed to compare the photochemical response of 18 Eucalyptus species, one Corimbia and one hybrid subjected to low temperature using two chilling treatments. Six-month-old plants were exposed to (1) gradual chilling (20–0 °C in four steps of 5 °C for 10 min) and abrupt chilling (20−5 °C in one step). Based on chlorophyll fluorescence parameters, eucalyptus species responded differently depending on how chilling was applied. E. tereticornis presented the best performance under chilling, regardless how it was imposed. The effective quantum yield of photosystem II was the best parameter to identify variation in photochemical responses of eucalyptus species to chilling. It was also observed that E. brassiana, C. citriodora, E. grandis, E. gunni, and E. resinifera were sensitive to the way chilling was applied, leading to differential photochemical response.

Parameters of Physiology, Nutrition and Quality of Eugenia dysenterica DC Seedlings Grown in Organic Substrates from the Agricultural Industry

Residues from agricultural activities might be used as substrates for production of seedlings. In this study it was aimed to evaluate the physiology, nutrition and quality of Eugenia dysenterica DC. seedlings grown in substrates derived from agricultural organic wastes. The wastes used were as follows: rice husks (RHs); fermented cattle manure (FCM); cattle manure compost (CMC), which contained corn silage and FCM; sugarcane bagasse (SCB); filter cake from sugar-alcohol mills (FC); and subsoil (SB). Four substrates were formulated from the wastes, namely SB+RH (1:1; v:v), SB+CMC (1:1), SB+FCM (3:1) and SCB+FC (3:2) and BioplantÒsubstrate was also used. The following characteristics were evaluated: the emergence and vigor percentages, biometric characteristics, seedling quality indices, gas exchange, chlorophyll a fluorescence and leaf nutrient levels. The seedling emergence was similar for all the substrates. The highest vigor was found in seedlings that were cultivated in SCB+FC, which was equal to the vigor observed in BioplantÒ. In general, the use of the SB+CMC substrate gave better seedling results for the biometric and nutritional characteristics, followed by SCB+FC. Most of the biometric characteristics showed a correlation with photosynthesis, electron transport rate and effective quantum yield of photosystem II, thus showing that these characteristics can be alternatives to the traditional quality indexes used for seedlings. The use of CMC, SCB and FC was shown to be appropriate for the production and nutritional supply of seedlings’ specie. The composition SB (subsoil)+CMC (1:1) proved to be the most suitable to produce E. dysenterica seedlings.

Chlorophyll fluorescence and oxidative stress endpoints to discriminate olive cultivars tolerance to drought and heat episodes

Abstract Climate change is increasing the frequency of heat waves accompanied by drought episodes. These challenges are increasing in the Mediterranean basin, where Olea europaea L. has an important ecological and economic role. Olive breeding programs have been focused on highly productive cultivars, while ancient cultivars may present higher tolerance to drought and heat resilience. Therefore, it is important to select traditional cultivars that may give reliable performances under the emerging climate change scenarios. In the present work, the differential physiological response of economically important traditional Portuguese olive cultivars, Cobrancosa, Cordovil de Castelo Branco (C.C. Branco), and Cordovil de Serpa (C. Serpa), to drought combined with heat are evaluated. Stress treatment had lowest impacts on water status in Cobrancosa. Also, this cultivar was less affected regarding pigments content, maximum and effective quantum yield of photosystem II (Fv/Fm and ΦPSII) and exhibited higher ability to trigger an antioxidant response. C.C. Branco was the most sensitive cultivar in response to pigments (carotenoids), Fv/Fm and ΦPSII, and cell membrane stability. Principal component analysis suggested that Cobrancosa has high potential to withstand climate change events, particularly drought combined with heat episodes, followed by C. Serpa and C.C. Branco.

Resistance mechanisms and their difference between the root and leaf of Microsorum pteropus – A novel potential aquatic cadmium hyperaccumulator

Microsorum pteropus (M. pteropus), an aquatic Polypodiaceae fern, was identified as a novel potential cadmium (Cd) hyperaccumulator in our previous study. This study reveals the Cd-resistance mechanisms and their difference between the root and leaf of M. pteropus based on analyses of photosynthesis, antioxidant systems and gene expression. A high level of Cd at 500μM was used to treat the samples to test the effects of this compound. Superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA) and flavonoids were used as indicators for antioxidant system changes. Five chlorophyll fluorescent parameters including the maximal photochemical efficiency of photosystem II (Fv/Fm), effective quantum yield of photosystem II (Y(II)), photochemical quenching (qP), nonphotochemical quenching (qN) and electron transport rate (ETR) were measured to determine the photosynthetic changes. RNA-sequencing analysis was used to study the changes in gene expression. The results showed that after exposure to high levels of Cd, the concentrations of enzymatic oxidants (SOD and POD) were significantly increased, while the MDA levels were significantly decreased. There were no significant changes for the chlorophyll fluorescent parameters during Cd stress, which indicates that M. pteropus is highly effective at protecting itself. Certain functional genes, including photosystem genes and secondary metabolites, had significantly altered levels of expression. Different Cd-resistance mechanisms were found between the root and leaf tissues of M. pteropus. The root tissues of M. pteropus resist Cd damage using antioxidants, while its leaf tissues mainly protect themselves using photosystem self-protection.

Individual and combined effects of soil waterlogging and compaction on physiological characteristics of wheat in southwestern China

The combined effects of soil waterlogging and compaction are important concerns in crop production. Two field experiments were performed over two seasons to examine the effects of soil waterlogging and high bulk density (BD) on the performance of winter wheat in terms of its agronomic and physiological traits. Trial 1 applied soil waterlogging at different stages (started at tillering, jointing, booting and anthesis). Trial 2 was conducted with soil waterlogging and compaction that created BD of the topsoil (1.6gcm−3). Resultsfrom trial 1 showed that the tillering stage was the most waterlogging-sensitive period. A 12% lower grain yield caused by waterlogging was primarily reflected in reductions in spike numbers. Waterlogging at jointing and booting stages reduced grain weight through decreased dry matter translocation. Resultsfrom the field trial 2 showed that soil compaction decreased grain yield by 4.8%, and waterlogging aggravated this reduction by 20.7% and 22.4% when fields were waterlogged for 2 weeks (WL2w) and 4 weeks (WL4w), respectively. A reduction in spike number from fewer tillers at stem elongation stage was the main reason for grain yield loss. Soil compaction combined with waterlogging duration did not affect root weight, but soil compaction reduced above ground biomass and root weight after the jointing stage. Furthermore, waterlogging accelerated leaf senescence, especially under compacted conditions, which significantly decreased photosynthetic capacity, resulting in a lower maximal PSII photochemical efficiency (Fv/Fm), apparent electron transport rate (ETR), effective quantum yield of photosystem II (ΦPSII) and photochemical quenching (qP). Root weight was positively related to the total above ground biomass; whereas the final grain yield was not linearly related to the shoot weight. SPAD value correlated positively with yield and PSII parameters (Fv/Fm, Fv/F0). The study concluded that the tillering stage was most susceptible to waterlogging, and soil compaction combined with waterlogging at tillering stage had a larger harmful effect on root and shoot growth during or after waterlogging. SPAD readings may be a good surrogate for photosynthetic activity under waterlogging and compaction conditions.

Effects of ultraviolet radiation on photosynthetic performance and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fixation in &amp;lt;i&amp;gt;Trichodesmium erythraeum&amp;lt;/i&amp;gt; IMS 101

Abstract. Biological effects of ultraviolet radiation (UVR; 280–400 nm) on marine primary producers are of general concern, as oceanic carbon fixers that contribute to the marine biological CO2 pump are being exposed to increasing UV irradiance due to global change and ozone depletion. We investigated the effects of UV-B (280–320 nm) and UV-A (320–400 nm) on the biogeochemically critical filamentous marine N2-fixing cyanobacterium Trichodesmium (strain IMS101) using a solar simulator as well as under natural solar radiation. Short exposure to UV-B, UV-A, or integrated total UVR significantly reduced the effective quantum yield of photosystem II (PSII) and photosynthetic carbon and N2 fixation rates. Cells acclimated to low light were more sensitive to UV exposure compared to high-light-grown ones, which had more UV-absorbing compounds, most likely mycosporine-like amino acids (MAAs). After acclimation under natural sunlight, the specific growth rate was lower (by up to 44 %), MAA content was higher, and average trichome length was shorter (by up to 22 %) in the full spectrum of solar radiation with UVR, than under a photosynthetically active radiation (PAR) alone treatment (400–700 nm). These results suggest that prior shipboard experiments in UV-opaque containers may have substantially overestimated in situ nitrogen fixation rates by Trichodesmium, and that natural and anthropogenic elevation of UV radiation intensity could significantly inhibit this vital source of new nitrogen to the current and future oligotrophic oceans.

Effects of controlled‐release potassium fertilizer on available potassium, photosynthetic performance, and yield of cotton

AbstractPotassium (K) is one of the major mineral elements required for normal growth of cotton. However, understanding the effect of controlled‐release K fertilizer on leaf photosynthesis and K use efficiency (KUE) of cotton is currently limited. A two‐year pot experiment was consecutively conducted in 2014 and 2015 with three kinds of K fertilizer including K2SO4, KCl, and polymer‐coated KCl (CRK), each at four application rates (0.00, 0.86, 1.73, and 2.59 g K plant−1, respectively). For each type of K fertilizer, the yield and K uptake of cotton increased but the KUE decreased with higher K fertilizer application. The release characteristics of K from CRK corresponded well to the K requirements during cotton growth. Plant‐available soil K, as well as leaf SPAD values, net photosynthetic rate (Pn), maximal photochemical efficiency (Fv/Fm), and effective quantum yield of photosystem II (ΦPSII) in CRK treatments were increased after full bloom stage compared to conventional K fertilizers under the same potassium application rate. Consequently, the CRK treatments significantly increased lint cotton yields by 8.1–32.7% and 3.7–20.8%, while the KUE increased by 15.5–54.8% and 14.5–45.4% compared to KCl and K2SO4 treatments, respectively. The results indicate that the application of CRK is intensively recommended to replace conventional potassium fertilizers for gaining greater yields and higher KUE of cotton.

High tolerance to high-light conditions for the protected species Ariocarpus kotschoubeyanus (Cactaceae).

We determined the seasonal ecophysiological performance under perennial plants and under high solar radiation for adult individuals from the 'living rock' cactus Ariocarpus kotschoubeyanus, which occurs equally under nurse plants and in open spaces. We evaluated the effective quantum yield of photosystem II (ΦPSII) and the dissipation of thermal energy [non-photochemical quenching (NPQ)] thorough the year. The maximum apparent electron transport rate (ETRmax) and the saturating photosynthetically active photon flux density for PSII (PFDsat) were also determined from rapid light curves. We found that although the ΦPSII was higher in shaded sites under potential nurse plants than in exposed sites, all values were close to the optimal value of 0.83. The high ΦPSII found for A. kotschoubeyanus plants suggests that they use a great proportion of the absorbed light for photosynthesis, under nurse plants as well as in open spaces. We also found higher NPQ values in exposed sites than in shaded ones but only in Autumn, thus reducing the risk of photoinhibition. In addition, the PFDsat was higher in exposed sites than in shaded ones in Spring, Summer and Autumn, but in Winter there were no differences between treatments. We also found high saturating light levels for ETR (PFDsat higher than 1378 μmol m-2 s-1) in all seasons but in winter for shaded and non-shaded plants. Our findings indicate that A. kotschoubeyanus plants use a great proportion of the light that they absorb for photosynthesis. This high tolerance to high-light conditions could explain why A. kotschoubeyanus do not show preferences for protected sites under nurse plants.

Rubisco mutants of Chlamydomonas reinhardtii display divergent photosynthetic parameters and lipid allocation.

Photosynthesis and lipid allocation were investigated in Rubisco small subunit mutants of the microalga Chlamydomonas reinhardtii. Comparative analyses were undertaken with cells grown photoheterotrophically under sulphur-replete or sulphur-depleted conditions. The Y67A Rubisco mutant, which has previously demonstrated a pronounced reduction in Rubisco levels and higher hydrogen production rates than the wild type, also shows the following divergences in photosynthetic phenotype and lipid allocation: (i) low Fv/Fm (maximum photochemical efficiency), (ii) low effective quantum yield of photosystem II (ΦPSII), (iii) low effectiveness at protection against high light intensities, (iv) a higher level of total lipids per pigment and (v) changes in the relative proportions of different fatty acids, with a marked decrease in unsaturated fatty acids (FAs). The most abundant thylakoid membrane lipid, monogalactosyldiacylglycerol, decreased in amount, while the neutral lipid/polar lipid ratio increased in the mutant. The low amount and activity of the mutated Rubisco Y67A enzyme seems to have an adverse effect on photosynthesis and causes changes in carbon allocation in terms of membrane fatty acid composition and storage lipid accumulation. Our results suggest that Rubisco mutants of Chlamydomonas might be useful in biodiesel production.

Ecophysiological traits of various genotypes of a green key alga in biological soil crusts from the semi-arid Colorado Plateau, USA

Biological soil crusts (BSCs) represent a micro-ecosystem consisting of various microorganisms including algae in drylands worldwide. The green algal genus Klebsormidium is a typical member of such communities, and because of its filamentous morphology and sticky cells, it plays an ecological key role in the stabilization of soil surfaces. In the present study, we investigated for the first time the phylogeny and ecophysiological performance of five BSC Klebsormidium strains from the semi-arid Colorado Plateau, USA. The molecular phylogeny of rbcL sequences showed that these strains belong to two subclades, which have been described before from mainly humid habitats. During controlled dehydration, the effective quantum yield of photosystem II decreased during 370–430 min of exposure. After controlled rehydration, all strains recovered between 32.9 and 97.6% of the control, but with significant differences depending on the genetic lineage. All five isolates grew between 18.1 and 27.9 °C, with isolate-specific optimal growth temperatures. Similarly, all strains were grown under increasing photon fluence rates from 4 to 110 μmol photons m−2 s−1 with optima under the higher tested light levels. Two strains showed inhibition at higher photon fluence rates and hence low light requirements for growth. Photosynthesis under increasing photon fluence rates up to 314 μmol photons m−2 s−1 indicated again low light requirements, but with no photoinhibition. All results underline a pronounced plasticity of the ecophysiological traits of the investigated Klebsormidium strains, which allow these terrestrial algae to exploit the environmental gradients within BSCs in arid regions.

F-actin reorganization upon de- and rehydration in the aeroterrestrial green alga Klebsormidium crenulatum

Filamentous actin (F-actin) is a dynamic network involved in many cellular processes like cell division and cytoplasmic streaming. While many studies have addressed the involvement of F-actin in different cellular processes in cultured cells, little is known on the reactions to environmental stress scenarios, where this system might have essential regulatory functions. We investigated here the de- and rehydration kinetics of breakdown and reassembly of F-actin in the streptophyte green alga Klebsormidium crenulatum. Measurements of the chlorophyll fluorescence (effective quantum yield of photosystem II [ΔF/Fm’]) via pulse amplitude modulation were performed as a measure for dehydration induced shut down of physiological activity, which ceased after 141±15min at ∼84% RH. We hypothesized that there is a link between this physiological parameter and the status of the F-actin system. Indeed, 20min of dehydration (ΔF/Fm’=0) leads to a breakdown of the fine cortical F-actin network as visualized by Atto 488 phalloidin staining, and dot-like structures remained. Already 10min after rehydration a beginning reassembly of F-actin is observed, after 25min the F-actin network appeared similar to untreated controls, indicating a full recovery. These results demonstrate the fast kinetics of F-actin dis- and reassembly likely contributing to cellular reorganization upon rehydration.

WATER DEFICIT ENSURES THE PHOTOCHEMICAL EFFICIENCY OF Copaifera langsdorffii Desf1

ABSTRACT The intensity and frequency of drought periods has increased according to climate change predictions. The fast overcome and recovery are important adaptive features for plant species found in regions presenting water shortage periods. Copaifera langsdorffii is a neotropical species that has developed leaves presenting physiological mechanisms and morphological adaptations that allow its survival under seasonal water stress. We aimed in this work to observe substantial physiological responses for water saving and damage representative to the photochemical reaction after exposed plants to water stress and to subsequent recovery. We found in plants mechanisms to control water loss through the lower stomatal conductance, even after rehydration. It goes against the rapid recovery of leaves, indicated by the relative water content values restored to previously unstressed plants. Stomatal conductance was the only variable presenting high plasticity index. In photochemical activity, the species presented higher photochemical quenching, electron transport rate and effective quantum yield of photosystem II when they were subjected to rehydration after water stress period. Our results suggest that C. langsdorffii presented rapid rehydration and higher photochemical efficiency even after water restriction. These data demonstrate that this species can be used as a model for physiological studies due to the adjustment developed in response to different environmental schemes.