Algae collection and chlorophyll extraction are two troublesome steps in the traditional methods used for the determination of chlorophyll concentration in natural water. A new method was established ...in this study for fast collection and extraction of chlorophyll. Based on our results, the optimum centrifugation condition for collecting algae was determined as: 5000
for 15 min at 4 °C, and the optimum dilution ratio of dimethyl sulfoxide: 90% acetone was 1:4. The specific steps were as follows: the algae in water samples were collected by centrifugation at 5000
at 4 °C for 15 min. The precipitated algae were suspended with 2 mL DMSO. Then the sample was transferred to a 15 mL centrifuge tube, and the tube was incubated at 65 °C for 1–2 h in the dark until the sample turned white. After cooling, the chlorophyll extract was diluted with 8 mL 90% acetone, before centrifugation at 5000
for 5 min. The absorbance values of the supernatants at 750, 664, 647 and 630 nm were used for the calculation of chlorophyll concentrations by the trichromatic equations. This new method saved the filter cost, simplified the extraction process, improved the algae acquisition efficiency, and accelerated the chlorophyll extraction rate.
To investigate the toxic effect and mechanism of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) in aquatic plants, in vivo and in vitro exposure to BDE-47 were conducted. After 14-d exposure to ...5–20 μg/L BDE-47, the growth of Lemna minor plants was significantly suppressed, and the chlorophyll and soluble protein contents in fronds markedly decreased. Accordingly, the photosynthetic efficiency (Fv/Fm, PI) decreased. When the thylakoid membranes isolated from healthy fronds was exposed to 5–20 mg/L BDE-47 directly in vitro for 1 h, the photosynthetic efficiency also decreased significantly. In both the in vitro (5–20 μg/L) and in vivo (5–20 mg/L) experiments, BDE-47 led to an increased plasma membrane permeability. Hence, we concluded that BDE-47 had a direct toxicity to photosynthetic membranes and plasma membranes. However, direct effects on the activities of peroxidase (POD), malate dehydrogenase (MDH) and nitroreductase (NR) were not observed by adding 5–20 mg/L BDE-47 into crude enzyme extracts. The malondialdehyde (MDA) and superoxide anion radical (O2−) contents in the BDE-47 treated fronds were higher than those in the control fronds, suggesting that L. minor can not effectively relieve reactive oxygen species (ROS). The data above indicates that BDE-47 is toxic to L. minor through acting directly on biomembranes, which induces the production of ROS and thus causes remarkable oxidative damage to cells.
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•BDE-47 at 5–20 μg/L had significant toxicity to L. minor.•BDE-47 caused a direct injury to plasma membrane and thylakoid membrane of L. minor.•BDE-47 had no effect on the enzyme activity of NR, POD, MDH in the cytoplasm.•BDE-47 induced remarkable oxidative damage in frond cells of L. minor.
Summary
R‐loops, three‐stranded nucleic acid structures consisting of a DNA: RNA hybrid and displaced single‐stranded DNA, play critical roles in gene expression and genome stability. How R‐loop ...homeostasis is integrated into chloroplast gene expression remains largely unknown.
We found an unexpected function of FtsHi1, an inner envelope membrane‐bound AAA‐ATPase in chloroplast R‐loop homeostasis of Arabidopsis thaliana.
Previously, this protein was shown to function as a component of the import motor complex for nuclear‐encoded chloroplast proteins. However, this study provides evidence that FtsHi1 is an ATP‐dependent helicase that efficiently unwinds both DNA–DNA and DNA–RNA duplexes, thereby preventing R‐loop accumulation. Over‐accumulation of R‐loops could impair chloroplast transcription but not necessarily genome integrity. The dual function of FtsHi1 in both protein import and chloroplast gene expression may be important to coordinate the biogenesis of nuclear‐ and chloroplast‐encoded subunits of multi‐protein photosynthetic complexes.
This study suggests a mechanical link between protein import and R‐loop homeostasis in chloroplasts of higher plants.
In the endoscopic images of bladder, accurate segmentation of different grade bladder tumor from blurred boundary regions and highly variable shapes is of great significance for doctors’ diagnosis ...and patients’ later treatment. We propose a nested attentional feature fusion segmentation network (NAFF-Net) based on the encoder-decoder structure formed by the combination of weighted pyramid pooling module (WPPM) and nested attentional feature fusion (NAFF). Among them, WPPM applies the cascade of atrous convolution to enhance the overall perceptual field while introducing adaptive weights to optimize multi-scale feature extraction, NAFF integrates deep semantic information into shallow feature maps, effectively focusing on edge and detail information in bladder tumor images. Additionally, a weighted mixed loss function is constructed to alleviate the impact of imbalance between positive and negative sample distribution on segmentation accuracy. Experiments illustrate the proposed NAFF-Net achieves better segmentation results compared to other mainstream models, with a MIoU of 84.05%, MPrecision of 91.52%, MRecall of 90.81%, and F1-score of 91.16%, and also achieves good results on the public datasets Kvasir-SEG and CVC-ClinicDB. Compared to other models, NAFF-Net has a smaller number of parameters, which is a significant advantage in model deployment.
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