Superoxide anions induce tension wood formation by promoting cambium cell activity

Abstract

Tension wood (TW), characterized by increased cambium cell proliferation and few vessels, is a classical model for the mechanical analysis of wood formation. In this study, we found higher superoxide anion (O2. −) levels in the cambium zone of poplar (Populus alba× P. glandulosa clone “84K”) TW than in that of opposite wood during gravistimulation. Treatment with an O2. − activator (methyl viologen) resulted in tension-wood-like xylem tissue formation, and transgenic plants with reduced cambium O2. − levels presented an attenuated gravity response. Time-course detection of O2. − and indole-3-acetic acid (IAA) levels revealed that auxin responses were enhanced following increases in O2. − levels, suggesting that IAA mediates TW induction downstream of O2. −. Rapid division but advanced programmed cell death in cambium cells was detected in both gravistimulated and O2. − activator-treated plants. These findings suggest that high O2. − levels trigger downstream IAA signaling to promote cambium cell proliferation and induce TW formation.