The protective role of melatonin in plants against various abiotic stresses have been widely demonstrated, but poorly explored in organ-specific responses and the transmission of melatonin signals across organs. In this study, the effects of melatonin with the root-irrigation method and the leaf-spraying method on the antioxidant system and photosynthetic machinery in maize seedlings under drought stress were investigated. The results showed that drought stress led to the rise in reactive oxygen species (ROS), severe cell death, and degradation of D1 protein, which were mitigated by the melatonin application. The application of melatonin improved the photosynthetic activities and alleviated the oxidative damages of maize seedlings under the drought stress. Compared with the leaf-spraying method, the root-irrigation method was more effective on enhancing drought tolerance. Moreover, maize seedlings made organ-specific physiological responses to the drought stress, and the physiological effects of melatonin varied with the dosage, application methods and plant organs. The signals of exogenous melatonin received by roots could affect the stress responses of leaves, and the melatonin signals perceived by leaves also led to changes in physiological metabolisms in roots under the stress. Consequently, the whole seedlings coordinated the different parts and made a systemic acclimation against the drought stress. Melatonin as a protective agent against abiotic stresses has a potential application prospect in the agricultural industry.

Biomedical device-associated infection (BAI) is a great challenge in modern clinical medicine. Therefore, developing efficient antibacterial materials is significantly important and meaningful for the improvement of medical treatment and people’s health. In the present work, we developed a strategy of surface functionalization for multifunctional antibacterial applications. A functionalized polyurethane (PU, a widely used biomedical material for hernia repairing) surface (PU-Au-PEG) with inherent antifouling and photothermal bactericidal properties was readily prepared based on a near-infrared (NIR)-responsive organic/inorganic hybrid coating which consists of gold nanorods (Au NRs) and polyethylene glycol (PEG). The PU-Au-PEG showed a high efficiency to resist adhesion of bacteria and exhibited effective photothermal bactericidal properties under 808 nm NIR irradiation, especially against multidrug-resistant bacteria. Furthermore, the PU-Au-PEG could inhibit biofilm formation long term. The biocompatibility of PU-Au-PEG was also proved by cytotoxicity and hemolysis tests. The in vivo photothermal antibacterial properties were first verified by a subcutaneous implantation animal model. Then, the anti-infection performance in a clinical scenario was studied with an infected hernia model. The results of animal experiment studies demonstrated excellent in vivo anti-infection performances of PU-Au-PEG. The present work provides a facile and promising approach to develop multifunctional biomedical devices.

Catheter-related infection is a great challenge to modern medicine, which causes significant economic burden and increases patient morbidity. Hence, there is a great requirement for functionalized surfaces with inherently antibacterial properties and biocompatibility that prevent bacterial colonization and attachment of blood cells. Herein, we developed a strategy for constructing polymer brushes with hierarchical architecture on polyurethane (PU) via surface-initiated atom-transfer radical polymerization (SI-ATRP). Surface-functionalized PU (PU-DMH) was readily prepared, which comprised of poly­(3-[dimethyl-[2-(2-methylprop-2-enoyloxy)­ethyl]­azaniumyl]­propane-1-sulfonate) (PDMAPS) brushes as the lower layer and antimicrobial peptide-conjugated poly­(methacrylic acid) (PMAA) brushes as the upper layer. The PU-DMH surface showed excellent bactericidal property against both Gram-positive and Gram-negative bacteria and could prevent accumulation of bacterial debris on surfaces. Simultaneously, the PU-DMH samples possessed good hemocompatibility and low cytotoxicity. Furthermore, the integrated antifouling and bactericidal properties of PU-DMH under hydrodynamic conditions were confirmed by an in vitro circulating model. The functionalized surface possessed persistent antifouling and bactericidal performances both under static and hydrodynamic conditions. The microbiological and histological results of animal experiments also verified the in vivo anti-infection performance. The present work might find promising clinical applications for preventing catheter-related infection.

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Rice (Oryza sativa L.) frequently suffers in late spring from severe damage due to cold spells, which causes the block of chlorophyll biosynthesis during early rice seedling greening. However, the inhibitory mechanism by which this occurs is still unclear. To explore the responsive mechanism of rice seedlings to low temperatures during greening, the effects of chilling stress on chlorophyll biosynthesis and plastid development were studied in rice seedlings. Chlorophyll biosynthesis was obviously inhibited and chlorophyll accumulation declined under low temperatures during greening. The decrease in chlorophyll synthesis was due to the inhibited synthesis of δ-aminolevulinic acid (ALA) and the suppression of conversion from protochlorophyllide (Pchlide) into chlorophylls (Chls). Meanwhile, the activities of glutamate-1-semialdehyde transaminase (GSA-AT), Mg-chelatase, and protochlorophyllide oxidoreductase (POR) were downregulated under low temperatures. Further investigations showed that chloroplasts at 18 °C had loose granum lamellae, while the thylakoid and lamellar structures of grana could hardly develop at 12 °C after 48 h of greening. Additionally, photosystem II (PSII) and photosystem I (PSI) proteins obviously declined in the stressed seedlings, to the point that the PSII and PSI proteins could hardly be detected after 48 h of greening at 12 °C. Furthermore, the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) and cell death were all induced by low temperature. Chilling stress had no effect on the development of epidermis cells, but the stomata were smaller under chilling stress than those at 28 °C. Taken together, our study promotes more comprehensive understanding in that chilling could inhibit chlorophyll biosynthesis and cause oxidative damages during greening.

Self-adaptive antibacterial surfaces with bacterium-triggered antifouling-bactericidal switching properties were readily constructed for the therapy of catheter-associated infection.

Multifunctional antibacterial materials have great significance for treating biomedical device-associated infections (BAIs). In the present work, a facile and rational strategy was developed to produce dualfunctional implants with antibacterial and osteointegration-promoting properties for the treatment of BAI. A titanium implant, as a representative demo of implants, was first functionalized with ethanediamine-functionalized poly(glycidyl methacrylate) (PGED) brushes. Then, low-molecularweight quaternized polyethyleneimine (QPEI, a cationic antibacterial agent) and alendronate (ALN, a clinically used drug with high affinity for bone minerals) were covalently conjugated onto PGED brushes to produce dual-functional dental implants (Ti-AQ). The QPEI component imparted Ti-AQ with antibacterial abilities, and the ALN component could balance the cytotoxicity of a cationic antibacterial agent, improving the biocompatibility for osteoblast cells. The effective performances of anti-infection and osteointegration were demonstrated in a BAI animal model. The results indicated that Ti-AQ inhibited bacterial infection at the early stage and enhanced the osteointegration and biomechanical properties between the implants and bone tissues at the late stage. This study will provide one facile and universal strategy for the design and development of novel multifunctional antibacterial implants.

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