Sodium chlorite

The ground biomass was sequentially extracted with 80% (v/v) ethanol, 100% ethanol, and chloroform/methanol (1:1[v/v]), and after centrifugation, the resulting cell wall residue (AIR) was vacuum-dried for 24 h at room temperature. Sequential fractionations were carried out at 10 mg/ml based on the starting dry weight of AIR in order to isolate fractions enriched for different types of cell wall components. AIR wall was suspended at 25°C in 50 mM ammonium oxalate, pH 5.0 for 24 h with constant shaking at 100 rpm. After incubation, the mixture was centrifuged at 4,000 g for 15 min at room temperature and the supernatant saved as the ammonium oxalate extract. The residual pellet was subsequently washed three times with the same volume of deionized water, centrifuged, and the supernatant discarded. The pellet was treated at 25°C with 50 mM Na₂CO₃, pH 10.0 (containing 0.5% (w/v) sodium borohydride) with constant shaking (100 rpm). After centrifugation, the supernatant was saved as the sodium carbonate extract. The washed residual pellet was re-suspended in 1 M KOH with 1% (w/v) sodium borohydride and incubated at 25°C for 24 h with constant shaking at 100 rpm. After incubation, the suspension was centrifuged at 4,000 g for 15 min, the supernatant collected and labeled as 1 M KOH extract, and stored at 4°C. The residual pellet from the 1 M KOH fraction was re-suspended in 4 M KOH with 1% (w/v) sodium borohydride and incubated at 25°C for 24 h with constant shaking at 100 rpm. After incubation, the suspension was centrifuged at 4,000 g for 15 min and the supernatant collected, labeled as 4 M KOH extract and stored at 4°C. The residual pellet from the 4 M KOH fraction was treated with 100 mM sodium chlorite at 70°C for 3 h to break down lignin polymers. After centrifugation, the supernatant was collected and labeled as chlorite extract. The residual pellet left after the sodium chlorite treatment was treated with 4 M KOH containing 1% (w/v) sodium borohydride extraction at 25°C for 24 h with constant shaking (100 rpm) and the supernatant collected and labeled as 4MKOH PC. The 1MKOH, 4MKOH, and 4MKOH PC fractions were neutralized using glacial acetic acid, dialyzed against six changes of de-ionized water at room temperature for 72 h, and lyophilized [55 ].

Sections of the 2nd internode of plants at the heading stage were stained with Toluidine Blue and Calcofluor White, and were then imaged using a light microscope (BX-61, Olympus). The lengths and widths of cells (n≥50) were measured using the ImageJ 1.32j software (https://imagej.nih.gov/ij/).
TEM was used to observe the thickness of cell walls in the veins of the third leaf in seedlings at the 3-leaf stage, as described previously (Li et al., 2017 (link)). Samples were post-fixed in 2% (w/v) OsO₄ for 1 h after extensively washing in PBS buffer and embedded using a Spurr Low Viscosity Embedding Kit (Sigma). Sections were cut using an Ultracut E ultra-microtome (Leica) and picked up onto formvar-coated copper grids. After post-staining with uranyl acetate and lead citrate, the specimens were viewed under a Hitachi H7500 TEM.
Atomic force microscopy (AFM) was used to observe the structure of cellulose microfibrils. The basal region of the 2nd internodes of plants at the heading stage were sectioned using a microtome (VT1000S, Leica). To remove lignin with a minor effect on cellulose, we used treatment with 8% acidic chlorite (1 mM HCl added to 1 g sodium chlorite) at 50 °C incubation, with two cycles of 24 h each. The sections were then washed with pure water at least five times and stored for subsequent AFM observations. We used a PicoPlus Molecular Imaging system together with a PicoScan 3000 Controller, and an Agilent multipurpose AFM scanner with open-loop was used for imaging. The whole system was situated on a PicoPlus Isolation Chamber to avoid environmental noise. All images were taken using non-contact, top magnetic AC (TopMAC) mode under PicoTREC (Agilent Technologies) and images of the topography were collected. All samples were imaged at an average scanning speed of one line per second with 512×512 pixels. At least three independent images were taken as biological replicates.

To prepare transparent bamboo, we sourced flattened bamboo boards (Phyllostachys heterocycla) directly from Zhejiang Dechang Bamboo-Wood Co., Ltd. in China as our raw material. Other chemicals, including sodium chlorite (NaClO₂, 80%), glacial acetic acid (CH₃COOH), absolute ethanol (C₂H₅OH), liquid sodium silicate (Na₂O·nSiO₂, m = 2.25), PFTS, and TMCS, were procured from Aladdin Reagent Co., Ltd. in Shanghai, China and used without further purification.