Fig. 5.

Eccentric xylem formed in the TW response is inhibited in ethylene-insensitive Populus trees. Wild-type control trees, transgenic trees expressing the dominant-negative mutant allele Atetr1-1 under the 35S (lines 1E and 3A) or LMX5 (lines 1 and 6) promoters, and 1-MCP-treated trees were grown in vitro and leaned to 30° for 12 days to induce the TW response. Xylem area was measured in the TW and opposite wood halves of the xylem in a defined internode, and these areas are expressed as a ratio to illustrate asymmetric growth. (A) The stimulation of xylem growth at the TW side was reduced in ethylene-insensitive trees (mean ± SE of 5 independent trees). Asterisks indicate statistically significant differences (Student's t test) between wild-type control trees and ethylene-insensitive trees *, P < 0.05; **, P < 0.01; ***, P < 0.001. (B–D) Cross-sections taken from wild type (B), wild type treated with 1-MCP (C), and transgenic tree pLMX5::etr1-1 (line 6) (D). The vertical lines across cross-sections indicate division between measured TW and opposite wood xylem areas. C indicates control; TW, tension wood half; OW, opposite wood half. (Scale bar: 200 μm.)