Figure 1.

H₂O₂ and O₂^.− Are Present in Epidermal Cells that Undergo Cell Death.

(A) Third node and cross section through a third node of a rice cv PG56 stem section stained with DAB to visualize H₂O₂. Stem sections were treated with 150 μM ethephon for 6 h. The inset shows hair-like structures on the epidermis that do not cover a root primordium (white rectangle). The bar in the inset = 0.5 mm.

(B) Percentage of epidermal patches above adventitious roots that showed H₂O₂ staining after treatment of stem sections with 150 μM ethephon for up to 10 h. DAB and ethephon were both applied at time 0 h. Results are averages (±se) from 19 to 48 stem sections analyzed per treatment. Each node contains 15 to 20 adventitious root primordia. The rate induced with ethephon at 6 h was significantly different from others at P < 0.001 (Tukey test).

(C) Third node and cross section through a third node of a rice cv PG56 stem section stained with NBT to visualize O₂^.−. Stem sections were treated with 150 μM ethephon for 6 h.

(D) Percentage of epidermal patches above adventitious roots that showed O₂^.− staining after treatment of stem sections with 150 μM ethephon for up to 10 h. NBT and ethephon were both applied at time 0 h. Results are averages (±se) from 32 to 49 stem sections analyzed per treatment. Rates are not significantly different at P < 0.001 (Tukey test).