Figure 1.

Mature cell walls pretreated with pectolyase showed a reconstituted expansin-induced extension under constant load using the extensometer in vitro. A, Growing apical 1-cm segments or nongrowing basal 1-cm segments of cucumber hypocotyls were frozen, thawed, abraded, pressed, and heated with water for 100 s in a microwave oven, and then stretched under tension in the bathing buffer (50 mm sodium acetate, pH 4.5) in an extensometer for 30 min, after which (indicated by an arrow) the bathing buffer was replaced with 0.1 mL of bathing buffer containing 2 mg mL⁻¹ of crude expansin. The growing apical cell walls showed a reconstituted expansin-induced extension (solid line; rate = 4.36 ± 0.39 μm min⁻¹), whereas the nongrowing mature basal walls did not respond to exogenous expansin (dashed line). B, The nongrowing basal segments were frozen, thawed, abraded, pressed, and heated with water for 100 s in a microwave oven, and then pretreated with 0.25 mg mL⁻¹ pectolyase in bathing buffer for 10 min at 25°C, washed with bathing buffer three times, and, finally, suspended under tension in the bathing buffer in an extensometer for 30 min, after which (indicated by an arrow) the bathing buffer was replaced with 0.1 mL of bathing buffer containing 2 mg mL⁻¹ of crude expansin (solid line; rate = 3.48 ± 0.25 μm min⁻¹) or bathing buffer alone (dashed line; no extension). The curve is representative of 10 samples, and the rate is the mean ± se from three independent experiments.