Despite the importance of stem cells in plant and animal development, the common mechanisms of stem cell maintenance in both systems have remained elusive. Recently, the importance of hydrogen peroxide (HO) signaling in priming stem cell differentiation has been extensively studied in animals. Here, we show that different forms of reactive oxygen species (ROS) have antagonistic roles in plant stem cell regulation, which were established by distinct spatiotemporal patterns of ROS-metabolizing enzymes. The superoxide anion (O2·-) is markedly enriched in stem cells to activate and maintain stemness, whereas HO is more abundant in the differentiating peripheral zone to promote stem cell differentiation. Moreover, HO negatively regulates O2·- biosynthesis in stem cells, and increasing HO levels or scavenging O2·- leads to the termination of stem cells. Our results provide a mechanistic framework for ROS-mediated control of plant stem cell fate and demonstrate that the balance between O2·- and HO is key to stem cell maintenance and differentiation.
Pt-based alloy catalysts may promise considerable mass activity (MA) for oxygen reduction but are generally unsustainable over long-term cycles, particularly in practical proton exchange membrane fuel cells (PEMFCs). Herein, we report a series of Pt-based intermetallic compounds (Pt3Co, PtCo, and Pt3Ti) enclosed by ultrathin Pt skin with an average particle size down to about 2.3 nm, which deliver outstanding cyclic MA and durability for oxygen reduction. By breaking size limitation during ordered atomic transformation in Pt alloy systems, the MA and durability of subsize Pt-based intermetallic compounds can be simultaneously optimized. The subsize scale was also found to enhance the stability of the membrane electrode through preventing the poisoning of catalysts by ionomers in humid fuel-cell conditions. We anticipate that subsize Pt-based intermetallic compounds set a good example for the rational design of high-performance oxygen reduction electrocatalysts for PEMFCs. Furthermore, the prevention of ionomer poisoning was identified as the critical parameter for assembling robust commercial membrane electrodes in PEMFCs.
Recently, liquid flow over monolayer graphene has been experimentally demonstrated to generate an induced voltage in the flow direction, and various physical mechanisms have been proposed to explain the electricity‐generating process between liquid and graphene. However, there are significant discrepancies in the reported results with non‐ionic liquid: the observed voltage responses with deionized (DI) water vary from lab to lab under presumably similar flowing conditions. Here, a graphene‐piezoelectric material heterostructure is proposed for harvesting energy from water flow; it is shown that the introduction of a piezoelectric template beneath graphene results in an obvious voltage output up to 0.1 V even with DI water. This potential arises from a continuous charging–discharging process in graphene, which is suggested to be a result of a relatively retarded screening effect of the water for the generated piezoelectric charges than that of the graphene layer, as revealed by first‐principles calculations. This work considers a dynamic charge interaction among water, graphene, and the substrate, highlighting the crucial role of the underlying substrate in the electricity‐generating process, which will greatly enhance understanding of the flow‐induced voltage and push the graphene‐water nanogenerator close to practical applications.
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