Figure 5.

Induction of Ectopic Epidermal Cell Death by Mechanical Stimulation Is Dependent on Ethylene and Mediated through ROS.

(A) Death of epidermal cells that are not localized above a root is induced by force (F) in rice cultivar PG56. Cell death is strictly confined to the site of force application (indicated by a dashed circle).

(B) Application of 58.88 mN of force significantly (*,** P < 0.001; t test) promotes death of epidermal cells above root primordia within 2 h. Epidermal cells that are not localized above a root do not undergo cell death in response to 150 μM of ethephon (E, blue line). Application of 58.88 mN of force promotes 30% ectopic cell death after 4 h (magenta line). Cell death is fully inhibited by 5 ppm of 1-MCP (M; ^a,b P < 0.001; t test) (4 h, gray square). Joint application of force and ethephon fully promotes death of epidermal cells that do not cover a root (F+E, green line). Ectopic cell death is fully inhibited by 5 ppm of 1-MCP (^a,b P < 0.001) (4 h, orange square) and is reduced to 70% by 1 μM of DPI (4 h, magenta square). Force in the presence of 50 mM of AT fully promoted ectopic cell death independent of ethylene perception as analyzed in the absence of 1-MCP (4 h, light magenta square) and in the presence of 5 ppm of 1-MCP (4 h, gray square). Values indicate means ± se (n = 10 for all data points except n = 3 for force + 50 mM of AT + 5 ppm of 1-MCP).

(C) Cross sections of epidermal cells overlying or not overlying a root primordium. Light micrograph (Top); autofluorescence (Bottom) highlighting cell walls (λ_ex= 360 to 370 nm, emission was detected with a BP_{420 nm} filter).

Bar in (A) = 100 μm; bars in (C) = 50 μm.