Figure 4.

Ethylene Promotes Root Growth via ROS Signaling and Consequently Generates a Mechanical Force.

(A) A stem section encompassing the third node was fixed in place, and a glass bead attached to a force sensor was placed on top of a root primordium of rice cultivar PG56. The insert shows a scanning electron micrograph of a node with bulging epidermis-covered primordia.

(B) Schematic presentation of a force sensor used for force measurements and of a root dummy used for pressure application. PC, computer.

(C) Forces generated above root primordia that were treated with or without 150 μM of ethephon (E) or with 150 μM of ethephon after pretreatment with 1 μM of DPI. Data are means (n = 3 to 6).

(D) Evans Blue staining of the epidermis overlying root primordia after 2 h of force (F) application with or without pretreatment with 5 ppm of 1-MCP as indicated.

(E) Dose-dependent cell death in response to 2 h of pressure application with a root dummy. The applied force corresponds to the maximal force measured in (C). *,** P < 0.001 (t test). Pretreatment with 1 or 5 ppm of 1-MCP was for 2 h. ^a,b P < 0.001 (t test). Pretreatment with 1 μM of DPI was for 3 h. Data are means (± se; n = 10 each data point).