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’) tension wood 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 tension wood induction downstream of O2.−. Rapid division but advanced programmed cell death (PCD) in cambium cells were 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 tension wood formation.