Extended Data Figure 2. Representative macroscopic behavior of onion epidermal cell wall strips during two force-extension cycles (a) and after endoglucanase Cel12A addition in a constant-force creep experiment (b).

(a) shows that the second extension is reversible (elastic) and the first extension results in plastic extension (approximately 200 μm in this example). Force-extension curves of this type are typical of primary cell walls^31–34. (b) shows that addition of Cel12A stimulated onion wall creep after a lag of 30–40 min. Similar creep responses were reported for cucumber and Arabidopsis walls²⁰. Experimental conditions: Onion epidermal wall strips (3 mm wide) were prepared as described in Methods (including 10-s heat inactivation), and incubated in 20 mM sodium acetate buffer, pH 4.5. In (a) the wall strip (3 mm between clamps) was stretched in two cycles at a rate of 3 mm/min until a holding force of 98 mN was reached. In (b) the epidermal was clamped at a constant force of 98 mN. At the time indicated by the arrow the buffer was exchanged for one containing 1 μg/mL Cel12A. These two experiments were carried out at least 3 times with similar results.