D5500

A pair of Helmholtz coils (GMW 3470) were used to generate a magnetic field opposite to gravity. The generated magnetic fields were detected and calibrated with a Gauss meter (LakeShore 410). The sample powder was sealed and sandwiched between two ITO-coated glass slides. This device was placed in the center between two coils, where the homogeneous magnetic fields can be generated (Figures 2C and S5). The external magnetic field enables the formation of magnetic pillars that bridge the two ITO coatings, allowing for the closure of a circuit. This circuit was connected with an electrometer/high-resistance meter (Keysight B2987A), to which 1 V was applied, and the current (I) was measured simultaneously. The in situ observation of the magnetic pillars was carried out with a digital single-lens reflex camera (Nikon D5500).

Skeletal preparations by Alcian Blue/Alizarin Red staining have also been described previously^{60 (link)}. Samples were fixed in 99.5% ethanol for 10 days, placed in acetone for 1 days, and stained in 0.3% alcian blue in 70% ethanol/0.1% alizarin red in distilled water/acetic acid/70% ethanol (1:1:1:17) for 12 h. After washing with distilled water, specimens were placed in 1% KOH for 5 days and cleared by incubation in 20, 50, and 80% glycerol steps. The photos of the stained sample were taken using the digital camera (D5500; Nikon).

A 5 mm mycelium plug of fungus (C. acutatum) from an actively growing plate was inoculated into the center of the detached pepper leaves of both CaChiIII7-silenced (pTRV2:CaChiIII7) and control (pTRV2:00) plants. To maintain high relative humidity, the petri dishes were promptly sealed with parafilm and incubated at 28 °C. The ImageJ tool was used to measure the infected area/hyphal extension and quantify the degree of infection [60 (link)]. The pathogen-infected leaves were evaluated and photographed at 72 hpi.
The accumulation of H₂O₂ was observed by placing the pathogen-infected leaves in 1 mg mL⁻¹ of DAB solution for 15 h. This was followed by the removal of chlorophyll from the stained leaves by boiling the samples in 95% absolute ethanol. In addition, the cell death of the healthy leaves and those inoculated with the pathogen was monitored by trypan blue staining. The lactophenol-trypan blue solution (lactic acid and glycerol 10 mL each, 10 g phenol, and 10 mg trypan blue mixed in 10 mL of ddH₂O) was used to stain the pepper leaves, while a chloral hydrate solution (2.5 g mL⁻¹ chloral hydrate) was used to de-stain them. The photographs were taken with a Nikon D5500.

With the classical dissection, we exposed the fine structure of the denticulate ligaments. Synsacrum bone surfaces were cleaned of flesh. The movable thoracic and caudal vertebrae were removed. The synsacrum surfaces were photographed (Nikon D5500, lens Nikon AF-S Nikkor 35 mm f/1.8G ED). Three perspectives are shown in Fig. 3A–C. The remaining classical dissection was performed under a fluorescent stereomicroscope (Leica M205 Fa, magnification 7.8–160×). Images from the microscope dissection were taken with the built-in camera (Leica DFC digital 7000-T, 2.8 megapixel sensor, pixel size $4.54 \mu m$ ). Related pictures in Figs. 3D, 9, and 8B have been cropped and annotated for clarity and were not otherwise altered.
To simplify the classical dissection the bones of the pelvic girdle were removed. The spinal canal wall was opened from the dorsal side, along the coronal plane aligned to the intervertebral foramina location. The spinal cord and the glycogen body were removed from the dorsal side of the spinal canal. The denticulate ligaments were photographed (Fig. 3D), and ligaments were manipulated with a pair of forceps to indicate their stretchability and connectivity (Fig. 9).

A 300 nm longpass filter (#46–417, Edmund Optics) was used to assess the reactivity of the PCIs to wavelengths longer than the germicidal (200–280 nm) UV-C range. For each experiment, one PCI was placed beneath the longpass filter on top of the plastic container and one PCI was placed on the digital sensor as an unfiltered control. Post-exposure color was measured using the RM200QC. In order to assess the reactivity of the PCIs to sunlight, both models of commercial PCI were taped to the same white background using double-sided tape and covered with black cardstock during transport outside. The exposure to sunlight began at 17:50 on May 30^th, 2020 in Berkeley, CA, USA, when the UV index [45 (link)] was reported as 1 by Apple Weather. The color change was recorded over 5 minutes via iPhone 8 video. Both pre- and post-exposure PCIs were imaged using the Nikon D5500 and quantified using the RM200QC.