Figure 4.

Isoxaben does not irreversibly damage protoplasts. Tobacco BY-2 protoplasts were cultured for 48 h in the presence of 2.5 μm isoxaben, rinsed three times thoroughly with culture medium, and then cultured for 7 d without isoxaben. Isoxaben's effects were reversed by removal of the cellulose inhibitor, and cell elongation proceeded normally (a). When the protoplasts were treated for a shorter time (2 h) with 2.5 μm isoxaben and were then washed and cultured in isoxaben-free culture medium, the cells stained positively for cellulose microfibrils via Cellefluor (1 μg mL⁻¹) within 60 min, revealing a quick reversal time for isoxaben's effects. Bars = 20 μm (a) and 2.5 μm (b).