Responses of photosynthesis-related genes in Sargassum horneri to high temperature stress.

Golden tide outbreak threatened the marine ecological environment. Sargassum horneri is a single dominant species of the Yellow Sea golden tide, which growth and development are affected by changes in sea water temperature. This study investigated the photosynthetic physiology of copper algae and found that the growth rate, chlorophyll a content, carotenoid content, Fv/Fm, and maximum electron transfer efficiency were significantly reduced, indicating that Sargassum horneri was under stress under high temperature. In this study, high-throughput sequencing was used to analyze the response mechanisms of photosynthesis-related genes in S. horneri under high temperature stress. The results showed that most of the photosynthesis-related genes in S. horneri were downregulated and photosynthesis was inhibited under high temperature stress. However, the expression levels of ferredoxin, ferredoxin-NADP reductase, light-harvesting protein complexes, and oxygen-evolving complex genes were significantly upregulated (P ≤ 0.05) after five days of high temperature treatment. This study found that photosynthesis related genes play a crucial role in regulating the photosynthetic response of S. horneri to high temperature stress.

Allelopathic Inhibition and Mechanism of Quercetin on Microcystis aeruginosa.

The utilization of allelochemicals to inhibit algal overgrowth is a promising approach for controlling harmful algal blooms (HABs). Quercetin has been found to have an allelopathic effect on algae. However, its responsive mechanism needs to be better understood. In the present study, the inhibitory effects of different quercetin concentrations on M. aeruginosa were evaluated, and the inhibition mechanisms were explored. The results demonstrated that quercetin significantly inhibited M. aeruginosa growth, and the inhibitory effect was concentration-dependent. The inhibition rate of 40 mg L-1 quercetin on algal density reached 90.79% after 96 h treatment. The concentration of chlorophyll-a (chl-a) in treatment groups with quercetin concentrations of 10, 20, and 40 mg L-1 decreased by 59.74%, 74.77%, and 80.66% at 96 h, respectively. Furthermore, quercetin affects photosynthesis and damages the cell membrane, respiratory system, and enzyme system. All photosynthetic fluorescence parameters, including the maximum photochemical quantum yield (Fv/Fm), the actual photochemical quantum yield (YII), the maximum relative electron transfer rate (rETRmax), and light use efficiency (α), exhibited a downtrend after exposure. After treatment with 20 mg L-1 quercetin, the nucleic acid and protein content in the algal solution increased, and the respiration rate of algae decreased significantly. Additionally, superoxide dismutase (SOD) activities significantly increased as a response to oxidative stress. In comparison, the activities of ribulose 1,5-biphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) decreased significantly. These results revealed that quercetin could inhibit M. aeruginosa by affecting its photosynthesis, respiration, cell membrane, and enzymic system. These results are promising for controlling M. aeruginosa effectively.

Accumulation and re-distribution of microplastics via aquatic plants and macroalgae - A review of field studies.

The aquatic plants and macroalgae are primary producers with major roles regarding the maintenance of ecosystems but their interaction with microplastics (MPs) has received less attention than animals. We summarize the methodologies used, the MPs abundances and their characteristics across the literature on MPs pollution in aquatic plants and macroalgae. The sampling and quantification of MPs still lacks consistency between studies, which increased the uncertainty in cross-comparisons. The abundance of MPs varied by orders of magnitude between species and were mostly fibers and polymers with large degrees of production and applications. Filamentous species contained more MPs than others. The average ratio of MPs between vegetated and unvegetated sites reached 3:1. The average ratio of MPs between the biotic and abiotic fractions reached 2193:1, suggesting a high level of retention in fields. Our findings supported that aquatic plants and macroalgae are critical in the plastic flux within the marine environments.