High-throughput single-cell RNA sequencing (scRNA-seq) has advantages over traditional RNAseq to explore spatiotemporal information on gene dynamic expressions in heterogenous tissues. We performed Drop-seq, a method for the dropwise sequestration of single cells for sequencing, on protoplasts from the differentiating xylem of Populus alba × Populus glandulosa. The scRNA-seq profiled 9,798 cells, which were grouped into 12 clusters. Through characterization of differentially expressed genes in each cluster and RNA in situ hybridizations, we identified vessel cells, fiber cells, ray parenchyma cells and xylem precursor cells. Diffusion pseudotime analyses revealed the differentiating trajectory of vessels, fiber cells and ray parenchyma cells and indicated a different differentiation process between vessels and fiber cells, and a similar differentiation process between fiber cells and ray parenchyma cells. We identified marker genes for each cell type (cluster) and key candidate regulators during developmental stages of xylem cell differentiation. Our study generates a high-resolution expression atlas of wood formation at the single cell level and provides valuable information on wood formation.

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Large-size scintillators with high efficiency and ultrafast radiation fluorescence have shown more potential in the applications to ionizing radiation detection of medical diagnosis, nuclear control and high-energy physics. Currently, although traditional scintillators have made tremendous progress in scintillation efficiency, there are still challenges left in fluorescence lifetime. Faced with that problem, we adopted 2-inch ZnO as the substrate and doped gallium as activator to realize an ultrafast fluorescence excited by α-ray, of which the decay time is only 600 ps that is the shortest scintillation decay time reported so far. The results show that the shallow donor related with gallium not only effectively suppresses band-edge self-absorption, but makes ultrafast radiation possible, which gets gallium-doped ZnO as a potential scintillator for high-quality ultrafast dynamic imaging proved.

Phosphorescence is a fascinating photoelectronic phenomenon usually observed in rareearth-doped inorganic crystals and organic molecular crystals, owning great potential in optical information storage, color display and biological dosimetry. Here, we present an ultralong intrinsic phosphorescence (>20,000 seconds) in AlN single-crystal scintillator through X-ray excitation. We suggest that the long afterglow emission originates from the intra-band transition related to native nitrogen vacancy. Some excited states formed by absorbing X-ray photons cannot satisfy the parity difference between initial and final states required by transition selection rule, so they cannot return to the ground state directly through radiation transitions but through several phonon-assisted intra-band transitions slowly. During this process, a long-term broad-spectra phosphorescence emission is formed. Investigating the X-ray excited phosphorescence emission in the AlN is of great significance to understanding the mechanism of phosphorescence in inorganic materials, and to realizing the practical applications in high-energy ray dosimetry.