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.

Arbuscular mycorrhizal fungi (AMF) are widespread and specialized soil symbiotic fungi, and the establishment of their symbiotic system is of great importance for adversity adaptation. To reveal the growth and photosynthetic characteristics of AMF–crop symbionts in response to heavy metal stress, this experiment investigated the effects of Rhizophagus irregularis (Ri) inoculation on the growth, photosynthetic gas exchange parameters, and chlorophyll fluorescence characteristics of hemp (Cannabis sativa L.) at a Cd concentration of 80 mg/kg. The results showed that (1) under Cd stress, the biomass of each plant structure in the Ri treatment was significantly higher than that in the noninoculation treatment (P < 0.05); (2) under Cd stress, the transpiration rate, stomatal conductance, net photosynthetic rate, PSII efficiency, apparent electron transport rate and photochemical quenching coefficient of the Ri inoculation group reached a maximum, with increases ranging from 1% to 28%; (3) inoculation of Ri significantly reduced Cd enrichment in leaves, which in turn significantly increased the transpiration rate, stomatal conductance, electron transfer rate, net photosynthetic rate and photosynthetic intensity, protecting PSII (P < 0.05); and (4) by measuring the light response curves of different treatments, the light saturation points of hemp inoculated with the Ri treatment reached 1448.4 μmol/m²/s, and the optical compensation point reached 24.0 μmol/m²/s under Cd stress. The Ri–hemp symbiont demonstrated high adaptability to weak light and high utilization efficiency of strong light under Cd stress. Our study showed that Ri–hemp symbiosis improves adaptation to Cd stress and promotes plant growth by regulating the photosynthetic gas exchange parameters and chlorophyll fluorescence parameters of plants. The Ri–hemp symbiosis is a promising technology for improving the productivity of Cd-contaminated soil.

The main intent of the current research was to appraise if combined application of hydrogen sulfide (H₂S, 0.2 mM) and silicon (Si 2.0 mM) could improve tolerance of tomato plants to arsenic (As as sodium hydrogen arsenate heptahydrate, 0.2 mM) stress. Plant growth, chlorophylls (Chl), PSII maximum efficiency (Fv/Fm), H₂S concentration and L-cysteine desulfhydrase activity were found to be suppressed, but leaf and root As, leaf proline content, phytochelatins, malondialdehyde (MDA) and H₂O₂ as well as the activity of lipoxygenase (LOX) increased under As stress. H₂S and Si supplied together or alone enhanced the concentrations of key antioxidant biomolecules such as ascorbic acid, and reduced glutathione and the activities of key antioxidant system enzymes including catalase (CAT), superoxide dismutase (SOD), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and glutathione S-transferase (GST). In comparison with individual application of H₂S or Si, the joint supplementation of both had better effect in improving growth and key biochemical processes, and reducing tissue As content, suggesting a putative collaborative role of both molecules in improving tolerance to As-toxicity in tomato plants.

We investigated physiological responses including calcification, photosynthesis and alterations to polar metabolites, in the scleractinian coral Stylophora pistillata exposed to different concentrations of polyethylene microplastics. Results showed that at high plastic concentrations (50 particles/mL nominal concentration) the photosynthetic efficiency of photosystem II in the coral symbiont was affected after 4 weeks of exposure. Both moderate and high (5 and 50 particles/mL nominal) concentrations of microplastics caused subtle but significant alterations to metabolite profiles of coral, as determined by Nuclear Magnetic Resonance (NMR) spectroscopy. Specifically, exposed corals were found to have increased levels of phosphorylated sugars and pyrimidine nucleobases that make up nucleotides, scyllo-inositol and a region containing overlapping proline and glutamate signals, compared to control animals. Together with the photo-physiological stress response observed and previously published literature, these findings support the hypothesis that microplastics disrupt host-symbiont signaling and that corals respond to this interference by increasing signaling and chemical support to the symbiotic zooxanthellae algae. These findings are also consistent with increased mucus production in corals exposed to microplastics described in previous studies. Considering the importance of coral reefs to marine ecosystems and their sensitivity to anthropogenic stressors, more research is needed to elucidate coral response mechanisms to microplastics under realistic exposure conditions.

Pharmacologically active compounds found in reclaimed wastewater irrigation or animal manure fertilizers pose potential risks for agriculture. The mechanism underlying the effects of ketoprofen on rice (Oryza sativa L.) seedlings was investigated. The results showed that low concentrations (0.5 mg L⁻¹) of ketoprofen slightly stimulate growth of rice seedlings, while high concentrations can significantly inhibit growth by reducing biomass and causing damage to roots. Ketoprofen affects photosynthetic pigment content (Chla, Chlb, and carotenoids) and chlorophyll synthesis gene (HEMA, HEMG, CHLD, CHLG, CHLM, and CAO) expression. Fluorescence parameters such as minimum fluorescence (F₀), maximum fluorescence (Fₘ), variable fluorescence (Fᵥ), potential photosynthetic capacity (Fᵥ/F₀), maximum quantum efficiency of PSII photochemistry (Fᵥ/Fₘ), electron transfer rate (ETR), and Y(II), Y(NPQ), Y(NO) values were affected, showing photosynthetic electron transfer was blocked. Active oxygen radical (O₂•−and H₂O₂), malondialdehyde and proline content increased. Superoxide dismutase, catalase and ascorbate peroxidase activities, glutathione content and antioxidant-related gene (FSD1, MSD1, CSD1, CSD2, CAT1, CAT2, CAT3, APX1, APX2) expression were induced. Higher integrated biomarker response values of eight oxidative stress response indexes were obtained at higher ketoprofen concentrations. Ultrastructure observation showed that ketoprofen causes cell structure damage, chloroplast swelling, increase in starch granules, and reduction in organelles. This study provides some suggested toxicological mechanisms and biological response indicators in rice due to stress from pharmacologically active compounds.

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.

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.

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.

This study investigated if atmospheric ammonia (NH3) pollution around a sheep farm influences the photosynthetic performance of the lichens Evernia prunastri and Pseudevernia furfuracea. Thalli of both species were transplanted for up to 30 days in a semi-arid region (Crete, Greece), at sites with concentrations of atmospheric ammonia of ca. 60 μg/m3 (at a sheep farm), ca. 15 μg/m3 (60 m from the sheep farm) and ca. 2 μg/m3 (a remote area 5 km away). Lichen photosynthesis was analysed by the chlorophyll a fluorescence emission to identify targets of ammonia pollution. The results indicated that the photosystem II of the two lichens exposed to NH3 is susceptible to this pollutant in the gas-phase. The parameter PIABS, a global index of photosynthetic performance that combines in a single expression the three functional steps of the photosynthetic activity (light absorption, excitation energy trapping, and conversion of excitation energy to electron transport) was much more sensitive to NH3 than the FV/FM ratio, one of the most commonly used stress indicators.

An increasing production and use of titanium dioxide nanoparticles (TiO₂ NPs) pose a huge threat to phytoplankton since they are largely released into aquatic environments, which represent a sink for TiO₂ NPs. However, toxicity and protective mechanisms of cyanobacteria in response to TiO₂ NPs remain elusive. Here we investigated toxic effects of two sizes of TiO₂ NPs (50 and 10 nm) and one bulk TiO₂ (200 nm) on a cyanobacterium, Synechocystis sp. and their possible protective mechanisms. We found that 10 nm TiO₂ NPs caused significant growth and photosynthesis inhibition in Synechocystis sp. cells, largely reflected in decreased growth rate (38%), operational PSII quantum yields (40%), phycocyanin (51%) and allophycocyanin (63%), and increased reactive oxygen species content (245%), superoxide dismutase activity (46%). Also, transcriptomic analysis of Synechocystis sp. exposure to 10 nm TiO₂ NPs showed the up-regulation of D1 and D2 protein genes (psbA and psbD), ferredoxin gene (petF) and F-type ATPase genes (e.g., atpB), and the down-regulation of psbM and psb28-2 in PS II. We further proposed a conceptual model to explore possible toxic and protective mechanisms for Synechocystis sp. under TiO₂ nanoparticle exposure. This study provides mechanistic insights into our understanding of Synechocystis sp. responses to TiO₂ NPs. This is essential for more accurate environmental risk assessment approaches of nanoparticles in aquatic ecosystems by governmental environmental agencies worldwide.