In vivo fluorescence imaging in the second near-infrared window (NIR-II) has been considered as a promising technique for visualizing mammals. However, the definition of the NIR-II region and the mechanism accounting for the excellent performance still need to be perfected. Herein, we simulate the photon propagation in the NIR region (to 2340 nm), confirm the positive contribution of moderate light absorption by water in intravital imaging and perfect the NIR-II window as 900–1880 nm, where 1400–1500 and 1700–1880 nm are defined as NIR-IIx and NIR-IIc regions, respectively. Moreover, 2080–2340 nm is newly proposed as the third near-infrared (NIR-III) window, which is believed to provide the best imaging quality. The wide-field fluorescence microscopy in the brain is performed around the NIR-IIx region, with excellent optical sectioning strength and the largest imaging depth of intravital NIR-II fluorescence microscopy to date. We also propose 1400 nm long-pass detection in off-peak NIR-II imaging whose performance exceeds that of NIR-IIb imaging, using bright fluorophores with short emission wavelength.

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FLOWERING PROMOTING FACTOR1 (FPF1), a small protein without any known domains, promotes flowering in several plants; however, its functional mechanism remains unknown. Here, we characterized two FPF1-like proteins, FPL1 and FPL7, which, in contrast, function as flowering repressors in Brachypodium distachyon. FPL1 and FPL7 interact with the components of the florigen activation complex (FAC) and inhibit FAC activity to restrict expression of its critical target, VERNALIZATION1 (VRN1) in leaves, thereby preventing over-accumulation of FLOWERING LOCUS T1 (FT1) at the juvenile stage. Further, VRN1 can directly bind to the FPL1 promoter and repress FPL1 expression; hence, as VRN1 gradually accumulates during the late vegetative stage, FAC is released. This accurate feedback regulation of FPL1 by VRN1 allows proper FT1 expression in leaves and ensures sufficient FAC formation in shoot apical meristems to trigger timely flowering. Overall, we define a sophisticated modulatory loop for flowering initiation in a temperate grass, providing insights toward resolving the molecular basis underlying fine-tuning flowering time in plants.

High-definition fluorescence imaging of deep-buried organs is still challenging. Here, we develop bright fluorophores emitting to 1700 nm by enhancing electron donating ability and reducing donor-acceptor distance. In parallel, the heavy water functions as the solvent of the delicately designed fluorophores, effectively reducing the fluorescent signal loss caused by the absorption by water. The near-infrared-II (NIR-II, 900-1880 nm) emission is eventually recovered and extended beyond 1400 nm. Compared with the spectral range beyond 1500 nm, the one beyond 1400 nm gives a more accurate fluorescence visualization of the hollow organs, owing to the absorption-induced scattering suppression. In addition, the intraluminal lesions containing much water are simultaneously negatively stained, leading to a stark contrast for precise diagnosis. Eventually, the intraluminally perfused fluorescent probes are excreted from mice and thus no obvious side effects emerge. This general method can provide new avenues for future biomedical imaging of deep and highly scattering tissues.