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The herbicidal effects of harmaline extracted from Peganum harmala seed on cell growth and photosynthesis of green algae Chlorella pyrenoidosa were investigated using chlorophyll a fluorescence and thermoluminescence techniques. Exposure to harmaline inhibited cell growth, pigments contents and oxygen evolution of C. pyrenoidosa. Oxygen evolution was more sensitive to harmaline toxicity than cell growth or the whole photosystem II (PSII) activity, maybe it was the first target site of harmaline. The JIP-test parameters showed that harmaline inhibited the donor side of PSII. Harmaline decreased photochemical efficiency and electron transport flow of PSII but increased the energy dissipation. The charge recombination was also affected by harmaline. Amplitude of the fast phase decreased and the slow phase increased at the highest level of harmaline. Electron transfer from QA(-) to QB was inhibited and backward electron transport flow from QA(-) to oxygen evolution complex was enhanced at 10 μg mL(-1) harmaline. Exposure to 10 μg mL(-1) harmaline caused appearance of C band in thermoluminescence. Exposure to 5 μg mL(-1) harmaline inhibited the formation of proton gradient. The highest concentration of harmaline treatment inhibited S3QB(-) charge recombination but promoted formation of QA(-)YD(+) charge pairs. P. harmala harmaline may be a promising herbicide because of its inhibition of cell growth, pigments synthesis, oxygen evolution and PSII activities., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Lichens are poikilohydric organisms and an important part of the ecosystem. They show high desiccation tolerance, but the mechanism of dehydration resistance still needs to be studied. The photosynthesis recovery of the photobiont in rehydrated lichen Cladonia stellaris after 11-year desiccation was investigated by simultaneously monitoring both photosystem I and II (PSI and PSII) activities. The responses of the photochemical efficiency and relative electron transport rate (rETR) of PSI and PSII, and the quantum yield of the cyclic electron flow (CEF) were measured using a Dual-PAM-100 system. PSI recovered rapidly, but PSII hardly recovered in C. stellaris during rehydration. The maximal photochemical efficiency of PSII (Fv/Fm) was generally very low and reached about just 0.4 during the rehydration. These results indicated that PSII had restored little and was largely inactivated during rehydration. The quantum yield of PSI recovered quickly to almost 0.9 within 4 h and remained constant at nearly 1 thereafter. The results showed that the activation of the CEF in the early stages of rehydration helped the rapid recovery of PSI. The quantum yield of the CEF made up a considerable fraction of the quantum yield of PSI during rehydration. A regulated excess energy dissipation mechanism and non-photochemical quenching (NPQ) also recovered. However, the small extent of the recovery of the NPQ was not enough to dissipate the excess energy during rehydration, which may be responsible for the weak activity of PSII during rehydration. The results indicated that both CEF and NPQ were essential during the rehydration of the photobiont in C. stellaris. The methods used in the measurements of chlorophyll a fluorescence and P700+ absorbance changes in this study provided a speedy and simple way to detect the physiological characteristics of the photobionts of lichen during rehydration. This work improves our understanding of the mechanism behind lichen's desiccation tolerance. [ABSTRACT FROM AUTHOR]

Nano-aluminium oxide (nAl 2 O 3 ) is one of the most widely used nanomaterials. However, nAl 2 O 3 toxicity mechanisms and potential beneficial effects on terrestrial plant physiology remain poorly understood. Such knowledge is essential for the development of robust nAl 2 O 3 risk assessment. In this study, we studied the influence of a 10-d exposure to a total selected concentration of 98 μM nAl 2 O 3 or to the equivalent molar concentration of ionic Al (AlCl 3 ) (196 μM) on the model plant Arabidopsis thaliana on the physiology (e.g., growth and photosynthesis, membrane damage) and the transcriptome using a high throughput state-of-the-art technology, RNA-seq. We found no evidence of nAl 2 O 3 toxicity on photosynthesis, growth and lipid peroxidation. Rather the nAl 2 O 3 treatment stimulated root weight and length by 48% and 39%, respectively as well as photosynthesis opening up the door to the use of nAl 2 O 3 in biotechnology and nano agriculture. Transcriptomic analyses indicate that the beneficial effect of nAl 2 O 3 was related to an increase in the transcription of several genes involved in root growth as well as in root nutrient uptake (e.g., up-regulation of the root hair-specific gene family and root development genes, POLARIS protein). By contrast, the ionic Al treatment decreased shoot and root weight of Arabidopsis thaliana by 57.01% and 45.15%, respectively. This toxic effect was coupled to a range of response at the gene transcription level including increase transcription of antioxidant-related genes and transcription of genes involved in plant defense response to pathogens. This work provides an integrated understanding at the molecular and physiological level of the effects of nAl 2 O 3 and ionic Al in Arabidopsis . [ABSTRACT FROM AUTHOR]

H 2 O 2 is an emerging biocide for bloom-forming cyanobacteria. It is important to investigate the H 2 O 2 scavenging ability of extracellular polymeric substances (EPS) of cyanobacteria because EPS with strong antioxidant activity may “waste” considerable amounts of H 2 O 2 before it kills the cells. In this study, the buffering capacity against H 2 O 2 of EPS from the bloom-forming cyanobacterium Microcystis aeruginosa was investigated. IC 50 values for the ability of EPS and vitamin C (VC) to scavenge 50% of the initial H 2 O 2 concentration were 0.097 and 0.28 mg mL −1 , respectively, indicating the higher H 2 O 2 scavenging activity of EPS than VC. Both proteins and polysaccharides are significantly decomposed by H 2 O 2 and the polysaccharides were more readily decomposed than proteins. H 2 O 2 consumed by the EPS accounted for 50% of the total amount of H 2 O 2 consumed by the cells. Cell growth and photosynthesis were reduced more for EPS-free cells than EPS coated cells when the cells were treated with 0.1 or 0.2 mg mL −1 H 2 O 2 , and the maximum photochemical efficiency Fv/Fm of EPS coated cells recovered to higher values than EPS-free cells. Concentrations of H 2 O 2 above 0.3 mg mL −1 completely inhibited photosynthesis and no recovery was observed for both EPS-free and EPS coated cells. This shows that EPS has some buffering capacity against the killing effect of H 2 O 2 on cyanobacterial cells. Such a strong H 2 O 2 scavenging ability of EPS is not favorable for killing bloom-forming cyanobacteria. The high H 2 O 2 scavenging capacity means considerable amounts of H 2 O 2 have to be used to break through the EPS barrier before H 2 O 2 exerts any killing effects on the cells. It is therefore necessary to determine the H 2 O 2 scavenging capacity of the EPS of various bloom-forming cyanobacteria so that the cost-effective amount of H 2 O 2 needed to be used for killing the cyanobacteria can be estimated. [ABSTRACT FROM AUTHOR]

Pollution with antibiotics poses a great risk to aquatic ecosystems. Although some toxic effects of antibiotics on photosystem II (PSII) have been documented, their toxicity to photosystem I (PSI) is still unclear. In this study, effects of ofloxacin on activities of both PSI and PSII of Microcystis aeruginosa (Kützing) Kützing were investigated. Exposure to 0.1 mg L − 1 ofloxacin led to increases in contents of chlorophyll a and carotenoids and photosynthetic activity of M. aeruginosa . PSI activity and its electron transport were not affected by 0.1 mg L − 1 ofloxacin. When M. aeruginosa was exposed to ≥10 mg L − 1 ofloxacin, the electron transport rates of PSI and PSII, the yield of cyclic electron flow (CEF) and the contribution of linear electron flow (LEF) to PSI decreased whereas Y(NA) (limitation of donor side of PSI) and Y(NO) (the quantum yield of non-regulated energy dissipation in PSII) significantly increased. CEF had a significant contribution to alleviating the inhibitory effect of ofloxacin on PSI of M. aeruginosa treated with low concentrations of ofloxacin. The protective role CEF for tolerance of PSI to the toxicity of ofloxacin decreased with increasing ofloxacin concentration. [ABSTRACT FROM AUTHOR]

The responses of photosystem II (PSII) activity of samara and leaf of Siberian elm (Ulmus pumila L.) to chilling (5°C) and freezing (-5°C & -15°C) temperature and their recovery were investigated. There was little difference in Fv/Fm between samara and leaf. Leaf showed more efficient photosynthesis (PIABS) and electron transport (fEo & ?o) than samara. Chilling and freezing had adverse impact on PSII function in both samara and leaf. Low temperature stress decreased photochemical efficiency (Fv/Fm & PIABS) and electron transport activity (?o, fEo & ETo/RC) in both leaf and samara. PSII of samara was more tolerant to low temperature stress than leaf. Photochemical efficiency (Fv/Fm) for chilled (at 5°C) or mild frozen (at - 5°C) samara or leaf showed a recovery trend. Severe freezing stress (-15°C) led to drastic and irreversible injuries to PSII in samara and leaf. The fact that samara has photosynthetic activity and is more tolerant to low temperature than leaf is of great ecological significance for seed development, population establishment and the northern distribution limit of Siberian elm in northern hemisphere. [ABSTRACT FROM AUTHOR]

It has been demonstrated that antimony (Sb) at concentrations ranging from 1.0 to 10.0 mg L−1 inhibits O2 evolution. Deeper insight into the influence of Sb on PSII was obtained with measurements of in vivo chlorophyll fluorescence. The donor and the acceptor sides of PSII were shown to be the target of Sb. Sb treatment induces inhibition of electron transport from Q to QB/Q and accumulation of P. S2(QAQB)− charge recombination and oxidation by PQ9 molecules became more important in Q reoxidation as the electron transfer in PSII was inhibited. Sb exposure caused a steady increase in the proportion of PSIIX and PSIIβ. These changes resulted in increased fluxes of dissipated energy and decreased index of photosynthesis performance, of maximum quantum yield, and of the overall photosynthetic driving force of PSII. [ABSTRACT FROM AUTHOR]

Abstract: Effects of LH on photosynthesis of Synechocystis sp. were investigated by a variety of in vivo chlorophyll fluorescence. O2 evolution and the photosystem II (PSII) activity were clearly inhibited by LH. Exposure to LH increased the proportion of PSIIβ and this weakened the connectivity between PSII units and hindered excitation energy-transfer between PSII units. LH decreased the density of the active photosynthetic reaction centers, inhibited electron transport, and increased the dissipated energy flux per reaction center. The inhibitory effect of LH on reoxidation process could be divided into several stages. LH first inhibited the electron transfer from to Q B by weakening the connectivity between and Q B, and PQ binding began taking part in reoxidation. At the second stage, the connectivity between and PQ pool was broken and inhibition on PQ binding occurred. At this stage, some began to be oxidized by S 2(Q A Q B)−. Finally, when the connectivity between and Q B and PQ was completely broken, all was oxidized through charge recombination. [Copyright &y& Elsevier]

Abstract: Amoxicillin is one of the widely used antibiotics of environmental concern. This study shows that amoxicillin has toxic effects on the photosynthesis of Synechocystis sp. Its inhibitory effects on photosystem II (PSII) of Synechocystis sp. were investigated by using a variety of in vivo chlorophyll fluorescence tests. The inhibitory effects of amoxicillin on PSII activity of Synechocystis sp. are concentration-dependent. Amoxicillin exposure leads to slowing down of electron transport on both donor side and acceptor side and causes accumulation of P680+. QA − reoxidation test revealed that amoxicillin hinders electron transfer from QA − to QB/QB − and more QA − is oxidized through S2(QAQB)− charge recombination. Analysis of PSII heterogeneity demonstrated that an exposure to amoxicillin increases the proportion of inactive PSII (PSIIX) centers and the proportion of PSII centers with small antenna (PSIIβ). These changes finally result in deterioration of full photosynthesis performance. [Copyright &y& Elsevier]

It is of environmental significance to study the leaching performance of additives from microplastics (MPs) and further evaluate the toxicity of leachate to microalgae. Here, we investigated the effects of accelerated aging on characteristics, leaching, and toxicity of commercial lead chromate pigmented MPs. Results show that aging of MPs caused surface cracks and fragmentation, increased their surface area and carbonyl contents, and promoted the release of lead chromate pigment. Chromium (Cr) and lead (Pb) tend to leach under acidic condition, rather than neutral and alkali environment. Aging treatment facilitates the leaching performance and a high concentration of NaCl solution also favors the leaching process. Toxicology experiments demonstrate that only high concentration of leachate (>10 μg L−1) exerted significant inhibitory influence (p < 0.005) on cell photosynthesis of Microcystis aeruginosa. The growth inhibition of algal cells remarkably increased with increasing leachate concentrations. We observed more inhibiting effects on cell growth and photosynthesis using the leachates of aged MPs. Longer aging time leads to more release of Cr and Pb, rendering higher toxicity to microalgae. These novel findings will benefit us from assessing the leaching behavior of additives in MPs and their toxicological risks to aquatic organisms. Image 1 • Aging of microplastics promoted the release of pigments. • Growth inhibition of algal cells increased with increasing leachate concentrations. • More inhibiting effects on cell growth and photosynthesis under aging conditions were observed. • Longer aging time led to more release of Cr and Pb, rendering higher toxicity to microalgae. Accelerated aging promotes the release of pigments from MPs and increases the toxicity of leachate to Microcystis aeruginosa. [ABSTRACT FROM AUTHOR]

Linoleic acid (LA), is the product of secondary metabolism secreted from Microcystis aeruginosa , and it exhibits allelopathic activity against eukaryotic algae. However, information about on the mechanisms associated with the inhibition of algal activity by LA is limited. In this study, Chlorella pyrenoidosa was treated with LA (20–120 μg L −1 ) for 4 days, and its growth inhibition and physiological responses were examined for potential toxic mechanisms. The photosynthetic efficiency of C. pyrenoidosa was inhibited by LA treatments, and the F v /F m parameter decreased significantly compared to that of controls; however, the photosynthetic pigment content did not change significantly. Peroxidase activity was enhanced, relieving oxidative damage in algae after LA treatments. However, superoxide dismutase and catalase were suppressed, ultimately leading to the aggravation of lipid peroxidation. Transcriptome-based gene expression analysis revealed that the 120 μg L −1 LA treatment significantly inhibited the transcription of genes related to photosynthesis, carbon metabolism, and amino acid metabolism in C. pyrenoidosa , suggesting that these genes might be key LA targets in C. pyrenoidosa . Moreover, the expression of genes involved in vitamin, lipid, nitrogen cycling, terpenoid, and ascorbate metabolism was also affected, suggesting that LA inhibits algal cell growth through multiple pathways. The identification of LA-responsive genes in C. pyrenoidosa provides new insight into LA stress responses in eukaryotic algae. [ABSTRACT FROM AUTHOR]

Copper nanoparticles (CuNPs) have been used in a broad range of applications. However, they are inevitably released into the marine environment, making it necessary to evaluate their potential effects on marine phytoplankton. In this study, the short-term (96 h) effects of CuNPs and CuSO 4 on Phacodactylum tricornutum growth, photosynthesis, reactive oxygen species production and transcription were assessed. It was found that high concentrations (40 μM) of CuNPs and CuSO 4 significantly inhibited the growth, photosynthesis and induced oxidative stress of P. tricornutum, while lower concentrations caused a hormetic response as indicated by a slight stimulation in algal growth. The high percentage of dissolved Cu (78–100%) in culture medium suggested that the dissolved Cu was the main driver of toxicity during CuNPs treatment. The algal cells upregulated electron transport chain-related genes to produce more energy and restore photosynthesis after 96 h of treatment with CuNPs and CuSO 4 . This study delineates the cellular mechanism behind the toxicity of CuNPs and CuSO 4 on marine diatoms. [ABSTRACT FROM AUTHOR]

Acidic copper mine tailings with high levels of heavy metals and arsenic pose a great risk to ecosystems and human beings. Physiological responses and phytoaccumulation of heavy metals and arsenic in Medicago sativa L. growing in soils with various proportions of acidic copper mine tailings were assessed in this study. Seed germination of M . sativa was enhanced by 5–10% tailings but inhibited at higher proportions (30% and 50%) of tailings. Seedling growth, cell membrane and photosynthesis were adversely affected when the plants were grown in soils with high proportions of tailings. The activities of antioxidant enzymes (catalase, superoxide dismutase and guaiocol peroxidase) increased with increasing proportions of tailings, indicating that the antioxidant system was not impaired and can tolerate the toxicity of mine tailings. The plants grew well in soil containing up to 50% of acidic copper mine tailings. Heavy metals and arsenic except Hg were overwhelmingly immobilized in roots. Medicago sativa is a promising plant species for revegetation and phytostabilization of acidic copper mine tailings in arid lands. However, the high mobility of Hg from root to shoot may pose risk to animals. [ABSTRACT FROM AUTHOR]