Relative Electron Transfer Rate Research Articles

Effects of solar radiation on photosynthetic physiology of barren stalk differentiation in maize

Barren stalks and kernel abortion are the major obstacles that hinder maize production. After many years of inbreeding, our group produced a pair of barren stalk/non-barren stalk near-isogenic lines SN98A/SN98B. Under weak light stress, the barren stalk rate is up to 98 % in SN98A but zero in SN98B. Therefore, we consider that SN98A is a weak light-sensitive inbred line whereas SN98B is insensitive. In the present study, the near-isogenic lines SN98A/SN98B were used as test materials to conduct cytological and photosynthetic physiological analyses of the physiological mechanism associated with the differences in maize barren stalk induced by weak light stress. The results showed that weak light stress increased the accumulation of reactive oxygen species (ROS), decreased the function of chloroplasts, destroyed the normal rosette structure, inhibited photosynthetic electron transport, and enhanced lipid peroxidation. The actual photochemical quantum efficiency for PSI (Y(I)) and PSII (Y(II)), relative electron transfer rate for PSI (ETR(I)) and PSII (ETR(II)), and the P700 activities decreased significantly in the leaves of SN98A and SN98B under weak light stress, where the decreases were greater in SN98A than SN98B. After 10 days of shading treatment, the O2·– production rate, H2O2 contents, the yield of regulated energy dissipation (Y(NPQ)), the donor side restriction for PSI (Y(ND)) and the quantum efficiency of cyclic electron flow photochemistry were always higher in SN98A than SN98B, and the antioxidant enzyme activities were always lower in SN98A than those in SN98B. These results show that SN98B has a stronger ability to remove ROS at its source, and maintain the integrity of the structure and function of the photosynthetic system. This self-protection mechanism is an important physiological reason for its adaptation to weak light.

Ocean acidification exacerbates copper toxicity in both juvenile and adult stages of the green tide alga Ulva linza

The toxicity of heavy metals to coastal organisms can be modulated by changes in pH due to progressive ocean acidification (OA). We investigated the combined impacts of copper and OA on different stages of the green macroalga Ulva linza, which is widely distributed in coastal waters, by growing the alga under the addition of Cu (control, 0.125 (medium, MCu), and 0.25 (high) μM, HCu) and elevated pCO2 of 1,000 μatm, predicted in the context of global change. The relative growth rates decreased significantly in both juvenile and adult thalli at HCu under OA conditions. The net photosynthetic and respiration rates, as well as the relative electron transfer rates for the adult thalli, also decreased under the combined impacts of HCu and OA, although no significant changes in the contents of photosynthetic pigments were detected. Our results suggest that Cu and OA act synergistically to reduce the growth and photosynthetic performance of U. linza, potentially prolonging its life cycle.

Opposite Growth Responses of Alexandrium minutum and Alexandrium catenella to Photoperiods and Temperatures.

Shift of phytoplankton niches from low to high latitudes has altered their experienced light exposure durations and temperatures. To explore this interactive effect, the growth, physiology, and cell compositions of smaller Alexandrium minutum and larger A. catenella, globally distributed toxic red tide dinoflagellates, were studied under a matrix of photoperiods (light:dark cycles of 8:16, 16:8, and 24:0) and temperatures (18 °C, 22 °C, 25 °C, and 28 °C). Under continuous growth light condition (L:D 24:0), the growth rate (µ) of small A. minutum increased from low to medium temperature, then decreased to high temperature, while the µ of large A. catenella continuously decreased with increasing temperatures. Shortened photoperiods reduced the µ of A. minutum, but enhanced that of A. catenella. As temperature increased, cellular Chl a content increased in both A. minutum and A. catenella, while the temperature-induced effect on RubisCO content was limited. Shortened photoperiods enhanced the Chl a but reduced RubisCO contents across temperatures. Moreover, shortened photoperiods enhanced photosynthetic capacities of both A. minutum and A. catenella, i.e., promoting the PSII photochemical quantum yield (FV/FM, ΦPSII), saturation irradiance (EK), and maximum relative electron transfer rate (rETRmax). Shortened photoperiods also enhanced dark respiration of A. minutum across temperatures, but reduced that of A. catenella, as well as the antioxidant activities of both species. Overall, A. minutum and A. catenella showed differential growth responses to photoperiods across temperatures, probably with cell size.

Responses of photosynthesis and P/Fe traits to P application in soybean under stress of low Fe.

We examined the effects of phosphorus (P) levels on photosynthetic and P/Fe traits of soybean under the stress of low Fe and their genotypic differences, to provide a theoretical basis for rational application of P and Fe fertilizer. Six P-efficient and six P-inefficient soybean varieties screened in the early stage were used as experimental materials. Four treatments of P:Fe ratio were set, including 0:30, 30:30, 150:30 and 300:30 (μmol·L-1). We measured chlorophyll fluorescence traits and P-Fe utilization efficiency in soybean. A stepwise regression equation was established with seed weight per plant. Pathway analysis was performed, with the response of P-efficient and P-inefficient soybean genotypes to different P:Fe treatments being comprehensively evaluated by factor scores. The results showed significant main and interactive effects of genotype and P:Fe on the relative electron transfer rate of photosystem Ⅱ (ETR) at beginning of flowering stage (R1), the proportion of the energy absorbed by photosystem Ⅱ dissipated into heat (NPQ) at R1 stage, and proportion of energy absorbed by photosystem Ⅱ devoted to the photochemical reaction (qL) at R1 stage. Results of canonical correlation analysis showed a negative correlation between P utilization efficiency of seed at full maturity stage (R8) and photosynthetic rate at R1 stage of P-efficient genotypes. Seed Fe utilization efficiency of P-inefficient genotypes at R8 stage was positively correlated with NPQ at R1 stage, but negatively correlated with qL at R1 stage. The actual photochemical efficiency of PSⅡ (ΦPSⅡ) at R1 stage was negatively correlated with P-efficient genotypes, but positively correlated with P-inefficient genotypes, which indicated that ΦPSⅡ at R1 stage was an important indicator for identifying soybean genotypes with different P efficiency under stress of low Fe. The comprehensive performance of P-efficient soybean genotypes decreased first and then increased with P level, while P-inefficient soybean genotypes increased first and then decreased. The inflection point of both genotypes appeared in P:Fe of 30:30. Thus, P:Fe ratio of 30:30 could be used as a threshold to identify soybean genotypes with different P efficiency under stress of low Fe. In conclusion, P fertilizer application should be equal to or greater than 1:1 (P:Fe) when planting P-efficient soybean genotypes in low Fe area, while P fertilizer application should not exceed 1:1 (P:Fe) when planting P-inefficient soybean genotypes.

Comparative transcriptome and cross-section analyses provide insights into the mechanisms underlying Sargassum fusiforme responses to the harmful algal bloom-forming dinoflagellate Karenia mikimotoi

The impacts of harmful algal blooms (HABs) on macrophytes have rarely been studied, although HABs are currently considered one of the major worldwide marine environmental threats. In this study, we incorporated photophysiology experimental data with paraffin-embedded section and transcriptome analysis of S. fusiforme to explore the effects of dense K. mikimotoi culture on the growth, photosynthetic activities, and leaf microstructure of S. fusiforme, as well as the expression of the genes related to its photosynthesis. The results showed that the fresh weight, Chl a contents, apparent photosynthetic efficiency (α) and relative electron transfer rate (rETRmax) of S. fusiforme seedlings cultivated for ten days with K. mikimotoi decreased by 53.60 %, 13.48 %, 6.30 % and 36.51 %, as compared with those cultivated without K. mikimotoi. The leaves of the S. fusiforme seedlings began to rot and detach from the stems after a week of cultivation with K. mikimotoi, and additional epidermic cells decomposed with prolonged exposure to the dinoflagellate. Transcripts of the genes related to photosystem reaction center subunits and photosynthesis antenna proteins were expressed differentially during the cultivation with K. mikimotoi, consistent with changes in the photosynthesis of S. fusiforme seedlings. These combined results indicate that the main mechanism for resistance to HABs is the formation of epidermis by a layer of tightly arranged cylindrical cells combined with differential expression of the photosynthesis-related genes.

Effects of nitrogen application rate on the photosynthetic pigment, leaf fluorescence characteristics, and yield of indica hybrid rice and their interrelations

A field experiment employing the rice cultivars Qyou6 and Yixiangyou2115 as materials and different nitrogen application rates was conducted in Huangping County, Guizhou Province in 2019 to determine the effects of nitrogen application rate on photosynthetic pigments, leaf fluorescence characteristics, yield, and their interrelations in indica hybrid rice. The results showed that photosynthetic pigment contents generally increased with increasing nitrogen application rate. As the nitrogen rate increased, the maximal quantum yield of PSII (Fv/Fm), actual quantum yield of PSII (ΦPSII), and relative electron transfer rate at PSII (ETR) first decreased and then increased at the booting stage; Fv/Fm and ΦPSII decreased while ETR first increased and then decreased at the heading stage; nevertheless, Fv/Fm and ΦPSII first decreased and then increased but ETR was just the opposite at the maturity stage. Non-photochemical quenching coefficient (qN) and quantum yield of regulatory energy dissipation at PSII (Y(NPQ)) first increased and then decreased whereas quantum yield of non-regulatory energy dissipation at PSII (Y(NO)) first decreased and then increased at the booting, heading, and maturity stages with increasing nitrogen application rate. Photochemical quenching coefficient (qP) showed an increasing trend as the nitrogen rate increased in the range of 150–300 kg/ha at the heading and maturity stages. Photosynthetic pigments, leaf fluorescence characteristics, and yield and its components were significantly correlated. First, chlorophylls a and b were significantly negatively correlated with Fv/Fm while significantly positively correlated with qP at the heading stage. Secondly, Carotenoids were significantly positively correlated with the effective panicle number (EPN) at the booting stage while significantly negatively correlated with the spikelets per panicle (SPP) at the heading stage. Chlorophyll a and carotenoids were significantly positively correlated with EPN but significantly negatively correlated with spikelet filling (SF) at the maturity stage. In addition, qP was significantly negatively correlated with EPN at the booting stage. At the heading stage, Fv/Fm and Y(NO) were significantly negatively correlated with EPN and SPP, respectively, and Fv/Fm and ΦPSII were significantly positively related to SF. Moreover, qP was extremely significantly positively related to EPN whereas Fv/Fm was extremely significantly negatively correlated with grain yield at the maturity stage. Appropriate nitrogen application rates can enhance photosynthetic pigment contents, improve the photochemical efficiency and proportion of the open part of the reaction center of PSII, and promote the quantum efficiency and self-protection ability of PSII, thereby increasing photosynthetic efficiency and yield. Under the conditions adopted in this experiment, a parabolic relationship was observed between the nitrogen application rate and grain yield. The regression analysis results showed that the best nitrogen application rate of indica hybrid rice is 168.16 kg ha−1 and the highest yield is 11,804.87 kg ha−1.

氮沉降背景下土壤微生物对入侵植物乌桕叶绿素荧光特征的影响

植物入侵会造成入侵地生态系统功能和稳定性的破坏。与原产地种源相比，入侵种源植物在生理学特性方面有所不同，使其在资源利用和抵抗环境胁迫具有较强的竞争优势。叶绿素荧光特性与植物光合作用效率密切相关，对植物生长具有重要作用。氮沉降加剧是全球变化的一个重要因子，土壤微生物对植物吸收利用土壤养分至关重要。通过施用细菌抑制剂（链霉素）和真菌抑制剂（扑海因）选择性抑制的土壤微生物活性，开展乌桕盆栽实验，在模拟氮沉降背景下，研究不同微生物群落如何影响入侵乌桕叶绿素荧光特性，有助于理解入侵植物的进化特征和入侵机制，为有效防控入侵植物并降低其对生态系统危害提供理论依据。以原产地地和入侵地两个种源乌桕（Triadica sebifera）为研究对象，在氮沉降条件下，通过调控土壤细菌和真菌，探讨两个种源乌桕叶绿素荧光参数差异。结果显示：氮沉降显著增加乌桕相对叶绿素含量（SPAD）、光系统II的最大量子产率（F_v/F_m）、非光化学猝灭（NPQ）和半饱和光强（I_k）。入侵种源乌桕比原产地具有较低SPAD。氮沉降与细菌抑制剂共同作用显著增强了F_v/F_m、NPQ和I_k，显著减弱了光能利用率（α）和SPAD。细菌抑制剂减缓了本地种源乌桕α，真菌抑制剂促进本地种源乌桕I_k，抑制入侵种源乌桕I_k，细菌和真菌抑制剂可显著降低原产地乌桕α。氮沉降与生物抑制剂可显著作用于乌桕叶片SPAD。氮沉降、土壤微生物和不同乌桕种源可共同作用于光系统Ⅱ实际光合量子产率Y（Ⅱ），α和潜在最大相对电子传递速率（ETR_max）。因此，氮沉降与生物抑制剂对乌桕叶绿素荧光特性具有协同作用，入侵种源乌桕对土壤微生物控制的响应不明显，在微生物控制条件下依然具有较强的适应能力，因而具有较强的入侵能力。;Plant invasions cause damage to both function and stability of invaded ecosystems. Compared with plants from the native origin, the invasive origin plants are different in physiological characteristics, which make them stronger in competitive ability in resource utilization and environmental stress resistance. The chlorophyll fluorescence characteristics are closely related to photosynthetic efficiency and play important roles in plant growth and expansion. Additionally, increased nitrogen deposition is an important factor of global change, while soil microorganisms are crucial for plants to absorb and utilize soil nutrients. By application of soil microbial inhibitors to control the activities of bacterial communities (by streptomycin) or fungi communities (by iprodione), study on invasive plant Triadica sebifera was carried out using pot experiment to understand how different microbial communities affect the chlorophyll fluorescence characteristics of T. sebifera from both the native and invasive origins under the background of simulated nitrogen deposition. The study will be helpful in understanding the evolutionary characteristics and invasion mechanism of invasive plants, and provide a theoretical basis for effectively preventing and controlling invasive plants, reducing their damage to the invaded ecosystems. The study was performed using a nested design, Triadica sebifera was used as the research object with two origins, including native and invasive origins. Under the condition of nitrogen deposition, the difference in the chlorophyll fluorescence parameters of the two origins of T. sebifera were investigated by regulating soil bacteria and fungus. Results showed that, nitrogen deposition significantly increased the relative chlorophyll content (SPAD), the maximum quantum yield of photosystem II (F_v/F_m), non-photochemical quenching (NPQ), half-satiety and light intensity (I_K) of T. sebifera. The invasive origin of T. sebifera had lower SPAD than the native origin. The combination of nitrogen deposition and bacterial inhibitor significantly enhanced F_v/F_m, NPQ and I_K, and significantly reduced light energy utilization (α) and the SPAD. The bacterial inhibitors decreased the native T. sebifera α. Fungi inhibitors promoted I_K of the native T. sebifera and inhibited I_k of the invasive T. sebifera. Nitrogen deposition, biological inhibitor and T. sebifera origin can act together on the PSII actual photosynthetic quantum yield Y(Ⅱ), α and potential maximum relative electron transfer rate (ETR_max). Therefore, nitrogen deposition and fungi inhibitors had a synergistic effect on the chlorophyll fluorescence characteristics of T. sebifera. The invasive origin of T. sebifera had no obvious response to the control of soil microorganisms, so it still had a strong adaptability under the control of microorganisms, and thereby had strong invasion ability.

Use of coumarin derivatives as activators in the peroxyoxalate system in organic and aqueous media

The peroxyoxalate system – base catalyzed reaction of oxalic ester derivatives with hydrogen peroxide in the presence of a fluorescent activator – is one of the most efficient chemiluminescence transformations known and widely utilized in analytical and bioanalytical applications. Coumarin derivatives have found widespread application as fluorescent labels for the determination of enzymatic activity in biological fluids and in fluorescence immunoassays, among others. In this work, we show that coumarin derivatives can be utilized as activators in the peroxyoxalate reaction (with two oxalic esters, including a new, environmentally compatible derivative) in anhydrous and aqueous systems, leading to reproducible kinetic results and singlet quantum yields similar to that obtained with commonly utilized activators. Quantum yields are lower in aqueous than in anhydrous medium, however still considerably high to allow the application in analytical and bioanalytical assays. The chemiluminescence parameters (singlet quantum yields at infinite activator concentration and relative electron transfer rate constants) determined in the systems indicate the occurrence of electron or charge transfer steps according to the Chemically Initiated Electron Exchange Luminescence (CIEEL) mechanism.

Kelp in IMTAs: small variations in inorganic nitrogen concentrations drive different physiological responses of Saccharina latissima

Kelps can be included in integrated multitrophic aquaculture (IMTA) where their growth and quality might benefit from the nutrient load released by other species like finfish and mussels transforming effluents from the cultured animals into valuable products. We studied how different nutrient concentrations affect growth, photosynthesis, chemical composition and pigment content of the kelp Saccharina latissima. We exposed kelps to natural seawater, water enriched to levels of ammonium and nitrate simulating finfish cage waste (IMTA1) and a combination of such enrichment with natural effluents coming from mussels (IMTA2). The algal biomass was higher and produced elevated total organic content when exposed to both IMTA1 and IMTA2. The photosynthetic responses in terms of relative electron transfer rate (rETRmax), PSII saturation irradiance (Ek) and total nitrogen content were also positively affected by both IMTA1 and IMTA2. We found a significant enhancement in pigment content only when algae were exposed to the strongest enrichment of our study (IMTA2). Finally, we found a positive relationship between rETRmax and growth, and the content of chlorophyll a and fucoxanthin. Our results show significant physiological responses of S. latissima to nutrient enrichment mimicking IMTA settings, as well as the benefit of added nutrients through a boost in photosynthetic activity that leads to higher kelp biomass and pigment production. This study suggests that modest nitrogen enrichment such as the one in our IMTA2 setup is enough to generate not only higher kelp biomass, but also an increased biomass quality with potentially higher market value.

Cadmium biosorption and biomass production by two freshwater microalgae Scenedesmus acutus and Chlorella pyrenoidosa: An integrated approach

Cadmium (Cd) contamination in different water bodies is a matter of serious concern, as it can cause biomagnification in our food chain up to several trophic levels. In this study, Cd toxicity was investigated in the micro-algae Chlorella pyrenoidosa and Scenedesmus acutus exposed to various concentrations of Cd for 96 h. The inhibitory and toxic effects of Cd2+ on growth and photosynthetic parameters of algae were demonstrated. The bioremediation potentials of these algae were investigated and bioremoval mechanisms were confirmed using qualitative electron microscopic assay such as scanning/transmission electron microscope (S/TEM). The photochemical quenching (Fv/Fm), quantum yield (YII), relative electron transfer rate (rETR) and non-photochemical quenching (NPQ) were inhibited significantly and reduced by ≥ 50% of the control at MIC 50 values. The C. pyrenoidosa and S. acutus biomass have shown 30% and 20% reduction in carbon content and 10% and 12% reduction in nitrogen content at MIC50 values of Cd2+ treatment, respectively. During bioremoval studies, C. pyrenoidosa and S. acutus have shown 45.45% and 57.14% Cd2+ removal of Cd2+ from initial concentration of 1.5 ppm. Out of total cadmium removal C. pyrenoidosa was reported 3% bioaccumulation and 97% biosorption. Whereas S. acutus showed 1.5% accumulation and 98.5% biosorption. The S/TEM images showed the surface accumulation and bioaccumulation of cadmium inside the cytoplasm, vacuoles, and chloroplast. Thus cultivating C. pyrenoidosa and S. acutus would be beneficial in Cd2+ contaminated water bodies as they serve the dual purpose by Cd remediation and algal biomass production.

Exogenous NaHCO3 enhances growth and lipid accumulation of the highly NaHCO3-tolerant Nannochloris sp. JB17

The extremely saline-alkaline soil in the northeast of China is rich in Na2CO3 and NaHCO3. Previously, we isolated the green alga Nannochloris sp. JB17 (JB17) from this soil and found that it was resistant to high concentrations of NaHCO3. In this study, the biochemical characteristics of JB17 cultured with NaHCO3 were studied by measuring growth and photosynthesis, and biomass, starch, and lipid production. The final cell density and maximum dry weight of JB17 cultured with 300 mM NaHCO3 were 1.528 and 1040.8 mg L−1, respectively, and were higher than those of JB17 cultured with 50 mM NaHCO3 (control). The maximum chlorophyll-a content and oxygen evolution rate under 300 mM NaHCO3 treatment were 26.5 mg g−1and 182 μmol O2 mg−1 Chl h−1, respectively, and were higher than those of the control. The addition of 300 mM NaHCO3 increased the relative electron transfer rate (rETR) and maximum relative electron transfer rate of JB17. The total starch and lipids contents of JB17 significantly increased from 215 to 356 mg g−1 and from 263 to 531 mg g−1, respectively, after the addition of 300 mM NaHCO3. Including NaHCO3 in the culture medium greatly stimulated the growth, biomass accumulation, and lipid productivity of JB17. These results indicate that the accumulation of starch and lipids in JB17 cultured with NaHCO3 might be related to the promotion of photosynthesis.

Effects of increased irradiance on biomass, photobiology, nutritional quality, and pigment composition of Arctic sea ice algae

Ice algae are key contributors to primary production and carbon fixation in the Arctic, and light availability is assumed to limit their growth and productivity. We investigated photo-physiological responses in sea ice algae to increased irradiance during a spring bloom in West Greenland. During a 14 d field experiment, light transmittance through sea ice was manipulated to provide 3 under-ice irradiance regimes: low (0.04), medium (0.08), and high (0.16) transmittances. Chlorophyll a decreased with elevated light availability relative to the control. Maximum dark-adapted photosynthetic efficiency (ΦPSII_max) showed an initially healthy and productive ice algae community (ΦPSII_max > 0.6), with ΦPSII_max decreasing markedly under high-light treatments. This was accompanied by a decrease in the light utilization coefficient (α) and photosynthetic capacity (maximum relative electron transfer rate), and a decrease in the ratio of mono- to polyunsaturated fatty acids. This was partly explained by a corresponding increase of photoprotective pigments (diadinoxanthin and diatoxanthin), and a development of mycosporine-like amino acids as identified from a distinctive spectral absorption peak at 360 nm. After 14 d, in situ fluorescence imaging revealed significant differences in ΦPSII_max between treatments of dark-adapted cells (i.e. those sampled before sunrise and after sunset), during diel cycles, with clear chronic photoinhibition in high and medium treatments. Data demonstrate the high sensitivity of spring-blooming Arctic sea ice algae to elevated irradiance caused by loss of snow cover. The predicted loss of snow cover on landfast ice will negatively impact ice algae, their potential primary production, and nutritional quality for higher trophic levels.

Algal density alleviates the elevated CO2‐caused reduction on growth ofPorphyra haitanensis(Bangiales, Rhodophyta), a species farmed in China

Growing of Pyropia haitanensis, a commercially farmed macroalga, usually increases their densities greatly during cultivation in natural habitats. To explore how the increased algal densities affect their photosynthetic responses to rising CO2, we compared the growth, cell components and photosynthesis of the thalli of P. haitanensis under a matrix of pCO2 levels (ambient CO2, 400 ppm; elevated CO2, 1,000 ppm) and biomass densities [low, 1.0 g fresh weight (FW) L−1; medium, 2.0 g FW L−1; high, 4.0 g FW L−1]. Under ambient CO2, the relative growth rate (RGR) was 5.87% d−1, 2.32% d−1 and 1.51% d−1 in low, medium and high densities, and elevated CO2 reduced the RGR by 27%, 25% and 12% respectively. Maximal photochemical quantum yield of photosystem II (FV/FM) was higher in low than in high densities, so were the light-utilized efficiency (α), saturation irradiance (EK) and maximum relative electron transfer rate (rETRmax). Elevated CO2 enhanced the FV/FM in low density but not in higher densities, as well as the α, EK and rETRmax. In addition, elevated CO2 reduced the content of chlorophyll a and enhanced that of carotenoids, but unaffected phycoerythrin, phycocyanin and soluble proteins. Our results indicate that the increased algal densities reduced both the growth and the photosynthesis of P. haitanensis and alleviated the elevated CO2-induced negative impact on growth and positive impact on photosynthesis. Moreover, the elevated CO2-induced reduction on growth and promotion on photosynthesis indicates that rising CO2 may enhance the loss of photosynthetic products of P. haitanensis through releasing organic matters.

Humic acid improves the physiological and photosynthetic characteristics of millet seedlings under drought stress

ABSTRACT We aimed to determine whether humic acid (HA) can alleviate the injury of millet caused by drought and its potential mechanism. Millet seeds (Jingu 21 and Zhangza 10) were soaked in different concentrations of HA (0, 50, 10, 200, and 300 mg L−1) for 12 h. The physiological and photosynthetic characteristics of millet seedlings, including growth parameters, osmotic regulators, antioxidase activity, photosynthesis, chlorophyll fluorescence, and P700 parameters, were determined before and after drought stress. HA significantly promoted the growth of millet seedlings under drought stress. Pretreatment with 100 mg L−1 or 200 mg L−1 HA significantly increased free proline, soluble protein, and activity of the antioxidant enzyme system (superoxide dismutase, peroxidase, and catalase) in both Zhangza 10 and Jingu 21. The accumulation of reactive oxygen species ( and H2O2) was reduced in HA treatments compared with that of the control (P < .05). Moreover, HA (100 mg L−1) significantly increased net photosynthetic rate, stomatal conductance, effective quantum yield of photosystem II, relative photosynthetic electron transfer rate of photosystem II, and photochemical quenching. HA also reduced intercellular CO2 concentration and non-photochemical quenching. Furthermore, 200 mg L−1 HA significantly increased the maximum P700, effective quantum yield of photosystem I, and relative photosynthetic electron transfer rate of photosystem I in Zhangza 10 and decreased non-photochemical energy dissipation in Jingu 21 and Zhangza 10 under drought stress. HA promoted the growth of millet seedlings under drought stress by promoting the osmotic adjustment ability and antioxidant capacity of seedlings and increased photosynthesis.

Monitoring the acclimatization of a Chlorella sp. From freshwater to hypersalinity using photosynthetic parameters of pulse amplitude modulated fluorometry

Contamination of freshwater raceway ponds impedes the commercial cultivation of microalgae. Acclimatization of freshwater microalgae to hypersaline conditions offers a means to reduce contamination. A freshwater Chlorella species was cultured in a gradient of salinities ranging from 5 to 40‰ and pulse amplitude modulated fluorometry recorded photosynthetic functioning. While the average salinity of seawater is 35‰, optimum acclimatization occurred at 20‰, at which point the growth rate (1.6 µg chl a L−1d−1) was not significantly different from the control (1.8 µg chl a L−1d−1). The maximum relative electron transfer rate was lower (9 to 12 µmol m−2s−1) at 5 to 20‰ as compared to 40‰ (28 µmol m−2s−1) where no algal growth was recorded. ATP and NADPH were thus shunted towards synthesis of molecules that offset cytoplasmic osmotic stress. Culturing this Chlorella strain in raceway ponds under saline conditions may reduce contamination and improve productivity.

Optimal chlorophyll fluorescence parameter selection for rapid and sensitive detection of lead toxicity to marine microalgae Nitzschia closterium based on chlorophyll fluorescence technology

Heavy metal pollution as one of the most serious pollution problems of marine environment, seriously threatens the safety of marine organism and human health, and will lead to potential risks for the marine ecological environment. In order to develop a rapid and sensitive toxicity detection method for marine heavy metals, in this study, marine diatom Nitzschia closterium was used as the test organism, and the effects of different concentrations of lead (Pb) on the five chlorophyll fluorescence parameters of N. closterium including the maximum photochemical quantum yield of PSII (Fv/Fm), the effective quantum yield of PSII photochemical energy conversion (ΦPSII), the effective absorption cross section of PSII photochemistry (σPSII′), the relative electron transfer rate of PSII (rP), and the PSII electron flux per unit volume (JVPII) at different exposure times were investigated based on chlorophyll fluorescence technology. By comparing with the photosynthetic activity fluorescence parameter Fv/Fm which is commonly used for toxicity analysis of pollutants using algae as test organisms, the optimal chlorophyll fluorescence parameter that could rapidly and sensitively determine Pb toxicity to N. closterium was selected. The results indicate that all the five chlorophyll fluorescence parameters of Fv/Fm, ΦPSII, σPSII′, rP and JVPII showed good dose-response relationships with Pb within 8 h exposure time, and they all could be used as endpoints to rapidly determine Pb toxicity to N. closterium. Among the five chlorophyll fluorescence parameters, JVPII was the most sensitive fluorescence parameter for detecting the toxicity of Pb to N. closterium within 6 h exposure. And for JVPII, the median effective concentration (EC50) values of Pb at 2, 4 and 6 h were 0.329, 0.068 and 0.040 mmol L−1, respectively. However, when the exposure time was 8 h, ΦPSII was the most sensitive fluorescence parameter for the toxicity detection of Pb, and the EC50 value of Pb at 8 h was 0.038 mmol L−1. This study will provide an important basis for the development of a rapid and sensitive detection method for the biological toxicity of marine heavy metals, and those results will be helpful for ecological risk assessment in marine environment.

Critical light-related gene expression varies in two different strains of the dinoflagellate Karlodinium veneficum in response to the light spectrum and light intensity

The toxic dinoflagellate Karlodinium veneficum is widely distributed in cosmopolitan estuaries and is responsible for massive fish mortality worldwide. Intraspecific biodiversity is important for the spread to various habitats, interspecific competition to dominate a population, and bloom formation and density maintenance. Strategies for light adaptation may help determine the ecological niches of different ecotypes. However, the mechanism of phenotypic biodiversity is still unclear. In this study, intraspecific differences in genetic regulatory mechanisms in response to varied light intensities and qualities were comparatively researched on two different strains isolated from coastal areas of the East China Sea, namely, GM2 and GM3. In GM2, the expression of genes in the Calvin cycle, namely, rbcL and SBPase, and a light-related gene that correlated with cellular motility, rhodopsin, were significantly inhibited under high light intensities. Thus, this strain was adapted to low light. In contrast, the gene expression levels were promoted by high light conditions in GM3. These upregulated genes in the GM3 strain probably compensated for the negative effects on the maximum quantum yields of PSII (Fv/Fm) under high light stress, which inhibited both strains, enabling GM3 to maintain a constant growth rate. Thus, this strain was adapted to high light. Compared with white light, monochromatic blue light had negative effects on Fv/Fm and the relative electron transfer rate (ETR) in both strains. Under blue light, gene expression levels of rbcL and SBPase in GM2 were inhibited; in contrast, the levels of these genes, especially rbcL, were promoted in GM3. rbcL was significantly upregulated in the blue light groups. Monochromatic red light promoted rhodopsin gene expression in the two strains in a similar manner. These intraspecific diverse responses to light play important roles in the motor characteristics, diel vertical migration, interspecific relationships and photosynthetic or phagotrophic activities of K. veneficum and can determine the population distribution, population maintenance and bloom formation.

Pigment concentration, photosynthetic performance, and fatty acid profile of sub-Antarctic brown macroalgae in different phases of development from the Magellan Region, Chile

Macroalgae Durvillaea antarctica, Lessonia flavicans, and Macrocystis pyrifera in distinct development phases from the ecoregion of Magellan (Chile) were analyzed by pulse amplitude modulated fluorometry under eight irradiation conditions (11 to 490 μmol photons m−2 s−1). Pigmentation was assessed by UV/Vis spectrophotometry (400 to 700 nm), and fatty acid (FA) profile was determined by gas chromatography using the standards of their respective methyl esters (0.625 to 20 mg mL−1). Photosynthetic efficiency had significant differences for L. flavicans (0.31 ± 0.01 to 0.38 ± 0.01 μmol e− m−2 s−1 (μmol photons m−2 s−1)-1) and M. pyrifera (0.26 ± 0.02 to 0.31 ± 0.03 μmol e− m−2 s−1 (μmol photons m−2 s−1)-1) for reproductive and vegetative phases, respectively. The relative maximum electron transfer rate varied significantly for L. flavicans (8.10 ± 0.84 to 12.40 ± 1.57 μmol e− s−1) and M. pyrifera (6.49 ± 1.30 to 12.89 ± 1.53 μmol e− s−1) in distinct development phases. Saturation irradiance analysis showed significant differences for D. antarctica, varying from 166.18 ± 14.33 (vegetative) to 132.98 ± 18.43 μmol photon m−2 s−1 (reproductive). The highest concentrations of pigments were found in reproductive M. pyrifera with 35.36 ± 0.21 of Chl a, 7.04 ± 0.93 of Chl c, and 15.75 ± 1.42 μg g−1 of fucoxanthin. Finally, the highest concentrations of total FAs were 35.24 ± 2.38% (saturated) and 22.02 ± 1.95% (monounsaturated) in M. pyrifera and 63.53 ± 3.36% (polyunsaturated) in D. antarctica. Therefore, the study showed significant differences for photosynthetic parameters and FA profiles correlating these results to the development phases of macroalgae.

Rising CO2 levels alter the responses of the red macroalga Pyropia yezoensis under light stress

Increased ocean uptake of CO2, due to rising atmospheric CO2 is leading to ocean acidification (OA) and alters light intensity due to increased turbidity and depth variation in seawater. Macroalgae have been found to alter their behavior in response to OA and other climate factors. In order to optimize farming strategies for economically important seaweeds, this study assesses the growth of Pyropia yezoensis at three different light intensities (HL:35%; ML:10%; LL:5%) and two CO2 concentrations (ambient CO2, 400 ppm; elevated CO2, 1000 ppm). Results show that P. yezoensis growth was significantly inhibited by decreased light intensity, due to reductions in photosynthesis, relative electron transfer rate (rETR) and carotenoid synthesis. However, under LL conditions, the relative growth rates (RGR), maximum net photosynthetic rate (Pmax) and maximum relative electron transfer rate (rETRmax) of PSI and PSII in P. yezoensis, were significantly enhanced under elevated CO2 concentrations. Phycocyanin (PC) and phycoerythrin (PE) levels in P. yezoensis were simultaneously increased under elevated CO2 concentrations. This study demonstrates that algal species may adapt to ocean acidification in the future and avoid light-induced growth inhibition.

Controlling Proton and Electron Transfer Rates to Enhance the Activity of an Oxygen Reduction Electrocatalyst

An electrochemical approach is developed that allows for the control of both proton and electron transfer rates in the O2 reduction reaction (ORR). A dinuclear Cu ORR catalyst was prepared that can be covalently attached to thiol-based self-assembled monolayers (SAMs) on Au electrodes using azide-alkyne click chemistry. Using this architecture, the electron transfer rate to the catalyst is modulated by changing the length of the SAM, and the proton transfer rate to the catalyst is controlled with an appended lipid membrane modified with proton carriers. By tuning the relative rates of proton and electron transfer, the current density of the lipid-covered catalyst is enhanced without altering its core molecular structure. This electrochemical platform will help identify optimal thermodynamic and kinetic parameters for ORR catalysts and catalysts of other reactions that involve the transfer of both protons and electrons.