Volatile organic compounds (VOCs) promote cyanobacteria dominating eutrophicated waters, with aquatic plant decrease and even disappearance. To uncover the toxic mechanism of cyanobacterial VOCs on aquatic plants, we investigated the growth, photosynthetic pigment levels, photosynthetic abilities and related gene expression in duckweed treated with β-cyclocitral and β-ionone, 2 main components in the VOCs. The levels of chlorophylls and carotenoids gradually declined with raising the concentration of the 2 compounds and prolonging the treatment time. Their decline should result from the down-regulation of 8 genes associated with photosynthetic pigment biosynthesis and up-regulation of 2 genes involved in carotenoid degradation. The reduction was also found in the photosystem II (PSII) efficiency and O₂ evolution rate, which should result from the lowered photosynthetic pigment levels and down-regulation of 38 genes related with photosynthetic process. The frond numbers, total frond area and fresh weight gradually decreased with raising the 2 compound concentration, which may result from the lowered photosynthetic abilities as well as down-regulated expression of 7 genes associated with growth-promoting hormone biosynthesis and signal transduction. It can be speculated that cyanobacterial VOCs may poison aquatic plants by lowering the photosynthesis and growth through altering related gene expression.

The present study investigated the physiological responses, photosynthetic activity, and microbial community structure of leaf-associated biofilms on the microphyte Vallisneria natans during a harmful algal bloom. Results of the physiological and photosynthetic indices (Fᵥ/Fₘ ratios [maximum quantum yield of photosystem II (PSII)]; malondialdehyde content; total chlorophyll; and activities of superoxide dismutase, catalase and peroxidase) indicated that algal blooms could cause inhibition of photosynthesis, oxidative stress and an antioxidant system stress response in Vallisneria natans leaf-associated biofilms. Multifractal analysis suggested that allelochemicals or algal organic matter released by cyanobacteria could reduce the surface roughness of the leaf. Microbial diversity analysis of the biofilms showed that algal blooms slightly altered the microbial community structure while the richness and evenness of the microbial composition remained stable. This study provided useful information to better understand the adverse effects of algal blooms on submerged macrophytes.

Concerns have been raised regarding the ecotoxicity of ionic liquids (ILs) owing to their wide usage in numerous fields. Three imidazolium chloride ILs with different numbers of methyl substituents, 1-decyl-imidazolium chloride ([C10IM]Cl), 1-decyl-3-methylimidazolium chloride ([C10MIM]Cl), and 1-decyl-2,3-dimethylimidazolium chloride ([C10DMIM]Cl), were examined to assess their effects on growth, photosynthesis pigments content, chlorophyll fluorescence, photosynthetic and respiration rate, and cellular ultrastructure of Scenedesmus obliquus. The results showed that algal growth was significantly inhibited by ILs treatments. The observed IC50,48h doses were 0.10 mg/L [C10IM]Cl, 0.01 mg/L [C10MIM]Cl, and 0.02 mg/L [C10DMIM]Cl. The chlorophyll a, chlorophyll b, and total chlorophyll content declined, and the chlorophyll fluorescence parameters, minimal fluorescence yield (F0), maximal fluorescence yield (Fm), maximum quantum yield of PSII photochemistry (Fv/Fm), effective quantum yield of PSII [Y(II)], non-photochemical quenching (NPQ) and non-photosynthetic losses yield [Y(NO)] were notably affected by ILs in a dose-dependent manner. ILs affected the primary photosynthetic reaction, impaired heat dissipation capability, and diminished photosynthetic efficiency, indicating negative effects on photosystem II. The photosynthetic and respiration rates of algal cells were also reduced due to the ILs treatments. The adverse effects of ILs on plasmolysis and chloroplast deformation were examined using ultrastructural analyses; chloroplast swelling and lamellar structure almost disappeared after the [C10MIM]Cl treatment, and an increased number of starch grains and vacuoles was observed after all ILs treatments. The results indicated that one-methyl-substituted ILs were more toxic than non-methyl-substituted ILs, which were also more toxic than di-methyl-substituted ILs. The toxicity of the examined ILs showed the following order: [C10IM]Cl < [C10DMIM]Cl ≤ [C10MIM]Cl.

Along the arid Arava, southern Israel, acacia trees (Acacia raddiana and Acacia tortilis) are considered keystone species. Yet they are threatened by the ongoing aquifer depletion for agriculture, the conversion of natural land to agricultural land, seed infestation by bruchid beetles, and the reduction in precipitation level in the region. In the acacia dominated Evrona reserve (southern Arava), adding to these threats are recurrent oil spills from an underground pipeline. We report here a study of the effects of contaminated soils, from a recent (December 2014) and a much older (1975) oil spills.The effects of local petroleum oil-contaminated soils on germination and early growing stages of the two acacia species were studied by comparisons with uncontaminated (control) soils from the same sites. For both acacia species, germination was significantly reduced in the 2014 oil-contaminated soils, whereas delayed in the 1975 oil-contaminated soil. There was no significant effect of oil volatile compounds on seed germination. At 105 days post transplanting (DPT), height, leaf number, stem diameter, and root growth were significantly smaller in the oil-contaminated soils. While photosynthetic performance (quantum yield of photosystem II) did not differ considerably between treatments, reductions of chlorophylls content and protein content were found in seedlings growing in the contaminated soils. Significant increases in superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities were found in roots of seedlings growing in oil-contaminated soils. These results demonstrate that seed germination and seedling growth of both acacia species were strongly restricted by oil contamination in soils, from both recent (2014) and a 40-year old (1975) oil spills.Such long-term effects of oil spills on local acacia seedlings could shift the structure of local acacia communities. These results should be taken into account by local authorities aiming to clean up and restore such polluted areas.

Carbon nanotubes can be either toxic or beneficial to plant growth and can also modulate toxicity of organic contaminants through surface sorption. The complex interacting toxic effects of carbon nanotubes and organic contaminants in plants have received little attention in the literature to date. In this study, the toxicity of multiwall carbon nanotubes (MWCNT, 50 mg/L) and paraquat (MV, 0.82 mg/L), separately or in combination, were evaluated at the physiological and the proteomic level in Arabidopsis thaliana for 7–14 days. The results revealed that the exposure to MWCNT had no inhibitory effect on the growth of shoots and leaves. Rather, MWCNT stimulated the relative electron transport rate and the effective photochemical quantum yield of PSII value as compared to the control by around 12% and lateral root production up to nearly 4-fold as compared to the control. The protective effect of MWCNT on MV toxicity on the root surface area could be quantitatively explained by the extent of MV adsorption on MWCNT and was related to stimulation of photosynthesis, antioxidant protection and number and area of lateral roots which in turn helped nutrient assimilation. The influence of MWCNT and MV on photosynthesis and oxidative stress at the physiological level was consistent with the proteomics analysis, with various over-expressed photosynthesis-related proteins (by more than 2 folds) and various under-expressed oxidative stress related proteins (by about 2–3 folds). This study brings new insights into the interactive effects of two xenobiotics (MWCNT and MV) on the physiology of a model plant.

Erythromycin is an antibiotic employed in the treatment of infections caused by Gram positive microorganisms and the increasing use has made it a contaminant of emerging concern in aqueous ecosystems. Cerium oxide nanoparticles (CeO₂ NPs), which are known to have catalytic and antioxidant properties, have also become contaminants of emerging concern. Due to the high reactivity of CeO₂ NPs, they can interact with erythromycin magnifying their effects or on the other hand, considering the redox potential of CeO₂ NPs, it can alleviate the toxicity of erythromycin. The present study was carried out to assess the toxicity of both single compounds as well as mixed on Chlamydomonas reinhardtii and Phaeodactylum tricornutum (freshwater and marine microalgae respectively) employed as target species in ecotoxicological tests. Mechanisms of oxidative damage and those harmful to the photosynthetic apparatus were studied in order to know the toxic mechanisms of erythromycin and the joint effects with CeO₂ NPs. Results showed that erythromycin inhibited the microalgae population growth and effective quantum yield of PSII (E.Q.Y.) in both microalgae. However, the freshwater microalgae Chlamydomonas reinhardtii was more sensitive than the marine diatom Phaeodactylum tricornutum. Responses related to the photosynthetic apparatus such as E.Q.Y. was affected by the exposure to erythromycin of both microalgae, as chloroplasts are target organelle for this antibiotic.Mixed experiments (CeO₂ NPs + erythromycin) showed the protective role of CeO₂ NPs in both microalgae preventing erythromycin toxicity in toxicological responses such as the growth of the microalgae population and E.Q.Y.

In this study, the accumulation and toxicity effect of 1–7 μM of Hg was determined during 24–72 h on two strains of Chlamydomonas reinhardtii, CC-125 and CC-503 as a cell wall-deficient mutant, by monitoring the growth rate and the maximum quantum yield of Photosystem II. In addition, the level of extracytoplasmic polyphosphates (polyP related to the cell wall) was determined to understand the polyP physiological role in Hg-treated algal cells. The results showed that the polyP level was higher in the strain CC-125 compared to CC-503. When algal cells were exposed to 1 and 3 μM of Hg, the accumulation of Hg was correlated with the degradation of polyP for both strains. These results suggested that the degradation of polyP participated in the sequestration of Hg. In fact, this mechanism might explain at 72 h the recovery of the polyP level, the efficiency of maximum PSII quantum yield, the low inhibition of growth rate, and the low accumulated Hg in algal biomass. Under the effect of 5 and 7 μM of Hg, the degradation of polyP was complete and could not be recovered, which was caused by a high accumulation and toxicity of Hg already at 24 h. Our results demonstrated that the change of polyP level was correlated with the accumulation and effect of Hg on algal cells during 24–72 h, which can be used as a biomarker of Hg toxicity. Therefore, this study suggested that extracytoplasmic polyP in C. reinhardtii contributed to the cellular tolerance for Hg.

Accurately predicting how marine biota are likely to respond to changing ocean conditions requires accurate simulation of interacting stressors, exposure regimes and recovery periods. Jellyfish populations have increased in some parts of the world and, despite few direct empirical tests, are hypothesised to be increasing because they are robust to a range of environmental stressors. Here, we investigated the effects of contaminated runoff on a zooxanthellate jellyfish by exposing juvenile Cassiopea sp. medusae to a photosystem II (PSII) herbicide, atrazine and reduced salinity conditions that occur following rainfall. Four levels of atrazine (0ngL⁻¹, 10ngL⁻¹, 2μgL⁻¹, 20μgL⁻¹) and three levels of salinity (35 ppt, 25 ppt, 17 ppt) were varied, mimicking the timeline of light, moderate and heavy rainfall events. Normal conditions were then slowly re-established over four days to mimic the recovery of the ecosystem post-rain and the experiment continued for a further 7 days to observe potential recovery of the medusae. Pulse-amplitude modulated (PAM) chlorophyll fluorescence, growth and bell contraction rates of medusae were measured. Medusae exposed to the combination of high atrazine and lowest salinity died. After 3 days of exposure, bell contraction rates were reduced by 88% and medusae were 16% smaller in the lowest salinity treatments. By Day 5 of the experiment, all medusae that survived the initial pulse event began to recover quickly. Although atrazine decreased YII under normal salinity conditions, YII was further reduced when medusae were exposed to both low salinity and atrazine simultaneously. Atrazine breakdown products were more concentrated in jellyfish tissues than atrazine at the end of the experiment, suggesting that although bioaccumulation occurred, atrazine was metabolised. Our results suggest that reduced salinity may increase the susceptibility of medusae to herbicide exposure during heavy rainfall events.

International audience | Research has been conducted within the framework of the French Initiative for Coral Reefs (IFRECOR) to assess pesticide pollution levels in the coral reef trophic webs in French Polynesia. Unexpected widespread contamination by herbicides was found in algae, fishes and macro-invertebrates located at various levels of the reef trophic web. Concentrations in organisms investigated were for the majority below the lowest observable effect level and do not pose a dietary risk to native population who subsist on these fish. However, the widespread contamination may affect the reef ecosystem in the future as coral symbiotic algae, Symbidinium sp. (Dinophyta) are particularly sensitive to photosystem II herbicides, particularly the substituted urea and triazine derivatives.