The shoot apical meristem (SAM) serves as a non-drying reservoir of pluripotent stem cells to supply new daughter cells forming above-ground tissues and organs such as leaves, stems, flowers and ...fruits throughout the life cycle of plants. Accordingly, the homeostasis control of stem cell division and differentiation must be an essential core mechanism for harmonic growth and development of plants as multicellular higher eukaryotes. Unlike animals, plants are sessile organisms and thus constantly face environmental factors, including abiotic stresses. Therefore, post-embryonic development derived from stem cells in the SAM likely interacts with surrounding abiotic stresses for plant adaptation and plastic development. For this reason, this review provides the most recent findings regarding comprehensive signaling networks involved in stem cell maintenance in the SAM, and then describes how stem cell signaling is related with abiotic stress response through involvement of phytohormones and reactive oxygen species in the SAM.
Salt stress severely affects plant growth and development. The plant growth and development of a sessile organism are continuously regulated and reformed in response to surrounding environmental ...stress stimuli, including salinity. In plants, postembryonic development is derived mainly from primary apical meristems of shoots and roots. Therefore, to understand plant tolerance and adaptation under salt stress conditions, it is essential to determine the stress response mechanisms related to growth and development based on the primary apical meristems. This paper reports that the biological roles of microRNAs, redox status, reactive oxygen species (ROS), nitric oxide (NO), and phytohormones, such as auxin and cytokinin, are important for salt tolerance, and are associated with growth and development in apical meristems. Moreover, the mutual relationship between the salt stress response and signaling associated with stem cell homeostasis in meristems is also considered.
Heterotrimeric G protein-mediated signaling plays a vital role in physiological and developmental processes in eukaryotes. On the other hand, because of the absence of a G protein-coupled receptor ...and self-activating mechanism of the Gα subunit, plants appear to have different regulatory mechanisms, which remain to be elucidated, compared to canonical G protein signaling established in animals. Here we report that
heterotrimeric G protein subunits, such as Gα (
) and Gβ (
), regulate plant growth under stress conditions through the analysis of heterotrimeric G protein mutants. Flg22-mediated growth inhibition in wild-type roots was found to be caused by a defect in the elongation zone, which was partially blocked in
but not
. These results suggest that
may negatively regulate plant growth under biotic stress conditions. In addition,
and
exhibited genetically opposite effects on
-mediated growth inhibition under heat stress conditions. Therefore, these results suggest that plant G protein signaling is probably related to stress-mediated growth regulation for developmental plasticity in response to biotic and abiotic stress conditions.
A metal-free organic dye (JH-1) and an unsymmetrical squaraine dye (SQ2) were used for co-sensitization of a flexible TiO2 electrode in order to obtain a broad spectral response in the visible light ...regions. Because of enhanced light absorption, the performance of the flexible plastic dye-sensitized solar cells (DSSCs) was enhanced. The dye concentration of co-sensitized TiO2 film was higher than that of individual dye-sensitized TiO2 film, leading to improved photovoltaic performance with the panchromatic light harvesting of JH-1 and SQ2 (350–720 nm). Optimum molar ratio of individual dye, dye concentration and adsorption kinetics onto the TiO2 photoelectrode, and ideal thickness of HS-TiO2 layer have been investigated. A flexible DSSC co-sensitized with the molar ratio of 60:40 (JH-1:SQ2) and TiO2 film thickness of 6 μm yielded a high photocurrent density of 12.32 mA cm−2, an open circuit voltage of 0.754 V, a fill factor of 0.68, and a power conversion efficiency of 6.31% under 1 sun illumination (100 mW cm−2). Interestingly, the co-sensitizers did not compete with each other for the absorption. Both the open circuit photovoltage and the photocurrent density were unexpectedly increased with co-sensitization which means that enhancement in photocurrents can be achieved without sacrificing the open circuit photovoltage for the co-sensitized solar cells, once the electron recombination and dye aggregation are retarded by the co-sensitization.
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•An organic dye (JH-1) and a squaraine dye (SQ2) were used for co-sensitization of a flexible TiO2 electrode.•Because of enhanced light absorption, the performance of the flexible DSSCs was enhanced.•A DSSC with a molar ratio of 60:40 (JH-1:SQ2) yielded a power conversion efficiency of 6.31%.•Both VOC and JSC were unexpectedly increased with co-sensitization.
The transcription factor LONG HYPOCOTYL5 (HY5) acts downstream of multiple families of the photoreceptors and promotes photomorphogenesis. Although it is well accepted that HY5 acts to regulate ...target gene expression, in vivo binding of HY5 to any of its target gene promoters has yet to be demonstrated. Here, we used a chromatin immunoprecipitation procedure to verify suspected in vivo HY5 binding sites. We demonstrated that in vivo association of HY5 with promoter targets is not altered under distinct light qualities or during light-to-dark transition. Coupled with DNA chip hybridization using a high-density 60-nucleotide oligomer microarray that contains one probe for every 500 nucleotides over the entire Arabidopsis thaliana genome, we mapped genome-wide in vivo HY5 binding sites. This analysis showed that HY5 binds preferentially to promoter regions in vivo and revealed >3000 chromosomal sites as putative HY5 binding targets. HY5 binding targets tend to be enriched in the early light-responsive genes and transcription factor genes. Our data thus support a model in which HY5 is a high hierarchical regulator of the transcriptional cascades for photomorphogenesis.
Key message
CLV3p-mediated phosphorylation of MPK3 and MPK6 occurs via CLV1 and BAM1 receptors to regulate the maintenance of SAM development.
The CLAVATA peptide-receptor (CLV3p-CLV1) pathway ...modulates a homeodomain master regulator WUSCHEL (WUS) transcription factor in the shoot apical meristem (SAM) with poorly defined signaling mechanisms. Here, we report that mitogen-activated protein kinases (MAPKs, also known as MPKs in plants) act in an intracellular signaling cascade to play an important role in the maintenance of SAM development. Interestingly, the application of exogenous CLV3p triggers rapid signaling in the SAM via dynamic activation of MPK3 and MPK6, which are positively regulated by both CLV1 and BARELY ANY MERISTEM 1 (BAM1) receptors. Surprisingly, the timing of MAPK activation is tightly correlated with the transcriptional repression of
WUS
expression in the SAM, indicating a fast CLV3p-CLV1/BAM1 signaling event. Furthermore, conditional
mpk3,6
double mutants exhibited CLV3p insensitivity in stem cell maintenance manifested by the persistent SAM growth in the presence of exogenous CLV3p signals, as well as elevated
WUS
expression and repressed WUS-specific target genes. Taken together, these results suggest that MPK3 and MPK6 activated by CLV3p signals through mainly CLV1 and BAM1 receptors are key regulators controlling stem cell homeostasis in the SAM.
Lead zirconate titanate (PbZr0.52Ti0.48O3, PZT) alloys have been extensively studied to be used for piezoelectric nanogenerators to harvest energy from mechanical motions. In this study, PZT ...nanofiber-based nanogenerators were fabricated to test their true piezoelectric performance without the triboelectric effect. Aligned PZT nanofibers were fabricated by a sol–gel electrospinning process. The thickness, area, and orientation of the PZT textile made by electrospinning a PZT solution onto multipair metal wires or metal mesh were controlled to form a composite textile. After the calcination, the PZT textile mixed with polydimethylsiloxane was placed between two flexible indium-doped tin oxide–polyethylene naphthalate substrates. The performance parameters of the nanogenerators were investigated under the bending motion, which excludes the triboelectric effect. An assembled nanogenerator of an area of 8 cm2 and a thickness of 80 μm could generate an electrical output voltage of 1.1 V and a current of 1.4 μA under the bending strain. The piezoelectric voltage depended on the thickness of the PZT textile, whereas the piezoelectric current depended on both the thickness and the area of the PZT textile. The electrical performance of the device was significantly affected by the orientation of the PZT fiber and the bending direction. The output voltage and the output current were strain-dependent, whereas the total integrated charge was independent of the strain rate. The properties of the flexible nanogenerator could be quantified to verify the pure piezoelectric performance of the device.
Highlights
A novel multi-band absorption-dominant electromagnetic interference (EMI) shielding film with transition metal-doped M-type strontium ferrites composite layer and a conductive grid is ...developed.
This film shows (1) ultralow EMI reflection less than 5%, (2) in multiple mmWave frequency bands corresponding to ferrites and grid characteristics, (3) with a broadband EMI shielding performance over 99.9% from 40 to 90 GHz.
Although there is a high demand for absorption-dominant electromagnetic interference (EMI) shielding materials for 5G millimeter-wave (mmWave) frequencies, most current shielding materials are based on reflection-dominant conductive materials. While there are few absorption-dominant shielding materials proposed with magnetic materials, their working frequencies are usually limited to under 30 GHz. In this study, a novel multi-band absorption-dominant EMI shielding film with M-type strontium ferrites and a conductive grid is proposed. This film shows ultralow EMI reflection of less than 5% in multiple mmWave frequency bands with sub-millimeter thicknesses, while shielding more than 99.9% of EMI. The ultralow reflection frequency bands are controllable by tuning the ferromagnetic resonance frequency of M-type strontium ferrites and composite layer geometries. Two examples of shielding films with ultralow reflection frequencies, one for 39 and 52 GHz 5G telecommunication bands and the other for 60 and 77 GHz autonomous radar bands, are presented. The remarkably low reflectance and thinness of the proposed films provide an important advancement toward the commercialization of EMI shielding materials for 5G mmWave applications.
The polyethylene lithium-ion battery separator is coated with a polymer by means of a roll-to-roll (R2R) gravure coating scheme to enhance the thermal stability. The polyvinylidene fluoride (PVDF) or ...polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) is gravure-coated, and the pores are fabricated based on online nonsolvent-induced phase separation (NIPS). N-methylpyrrolidone is used as a solvent, and deionized water or a methanol mixture thereof is exploited as a nonsolvent in NIPS. Scanning electron microscopy confirms that the polymer film is formed and that the pores are well developed. The thermal shrinkage decreased by 20.0% and 23.2% compared to that of the bare separator due to the coating of PVDF and PVDF-HFP, respectively. The R2R gravure coating scheme is proven to be fully functional to tailor the properties of lithium-ion battery separators.
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