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    Amino-functionalized SiO2 microbeads optimize photosynthetic performance, gene expression, ROS production and antioxidant status in chromium and copper-exposed Zea mays
    (Elsevier Sci Ltd, 2023) Alp-Turgut, Fatma Nur; Yildiztugay, Evren; Ozfidan-Konakci, Ceyda; Sargin, Idris
    The objective of the current study was to assess the potential of the amino-functionalized SiO2 microbeads (S) in improving the tolerance of maize to chromium and/or copper toxicity. For this purpose, Zea mays L. cv. DKC5685 was grown by exposure at different S concentrations (100-500 mg L-1) alone and with 200 mu M chromium (Cr stress) and 100 mu M copper (Cu stress) for 7 days. The photosynthesis-related parameters (Fv/Fm, Fv/Fo), relative growth rate (RGR), and relative water content (RWC) levels were suppressed under Cr and/or Cu stresses. In addition, stress altered antioxidant activities and gas exchange parameters. S applications abolished the negative impacts of stress on the physiological state of the photosynthetic system, potential photochemical efficiency and chlorophyll fluorescence. S increased the performance index by reversing the detrimental effects on the electron flow rate through the PSII electron transport flux and electron transfer from the decreased plastoquinone pool to the PSI reaction center. Following exposure to S, the effects of stress on photosystem I-associated reaction center proteins were rearranged by induced expression levels of PsaA and PsaB genes. S treatments had potent ROS scavengers in maize leaves. In the Cr+S groups, the AsA-GSH cycle was regulated by increasing the activities of all the responsible enzymes mentioned above, such as SOD, CAT, APX and GR, and the accumulation of H2O2 and TBARS effectively removed. CAT and POX activities in Cu+S groups were not effective in these adjustments. In Cr+Cu+S applications, although H2O2 and TBARS contents were reduced as evidenced by ROS visualization using fluorescence of dye, AsA regeneration could not be achieved, and low tAsA/DHA levels were detected. Our results show that amino-functionalized SiO2 microbeads have significant promise to offer resistance to maize by minimizing oxidative damage brought on by heavy metal uptake and preserving the metabolic processes involved in photosynthesis.
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    Antibacterial potentials of carbon dots immobilized on chitosan and glass surfaces
    (Elsevier, 2024) Ghaibullah, Yanar Najmalden Ghaibullah; Foto, Egemen; Ozdemir, Naciye; Foto, Fatma Zilifdar; Arslan, Gulsin; Sargin, Idris
    Due to their antibacterial activity, chitosan-carbon dot composites possess great potential for pharmaceuticals, medicine, and food preservation. Conducting a comprehensive study of the interactions between chitosan, carbon dots, and bacteria is crucial to understanding the processes behind applying these composites. This study aimed to immobilize carbon dots (C-dots) synthesized from Elaeagnus angustifolia fruits on chitosan and glass microbeads' surfaces, to characterize the test materials obtained after synthesis and immobilization, and to investigate their antibacterial potentials.C-dot synthesis was carried out from water extract in an acidic medium with the help of microwave irradiation, and their structural and optical properties were characterized by TEM, XRD, FT-IR, UV-vis, Zeta potential, and fluorescence methods. The surface of the glass microbeads was first activated and functionalized with surface amine groups with a silaning agent. C-dots were immobilized on both glass and chitosan microbeads using a crosslinking agent. Antibacterial potentials of nine different test materials, obtained before or after immobilization, were evaluated both qualitatively (MIC and MBC) and quantitatively (GI50) on E. coli, S. typhimurium, B. subtilis, and S. aureus, with the standard broth microdilution method.FT-IR and SEM-EDX analyses showed that C-dots were immobilized on chitosan (<1 mm) and glass (<100 mu m) microbead surfaces. C-dots reduced the cell viability by similar to 25 % on S. typhimurium and B. subtilis (MIC = 25 mg/ mL). It was also found that the highest antibacterial effect was recorded for C-dots-glass microbeads, which had a toxic effect of 43 % on S. aureus. In addition, binding C-dots to glass microbeads increased the antibacterial effect selectively in Gram-positive bacteria, while binding to chitosan microbeads was effective in all bacteria. The study showed that the antibacterial potential of C-dots-chitosan microbeads is more effective than C-dots-glass microbeads. C-dots could be used as carbon-based nanomaterials in antibacterial surface preparation once immobilized.