Wood formation in rolC transgenic aspen trees

Wood formation and structure of 3-year-old 35S-rolC transgenic aspen (Populus tremula L. x tremuloides Michx.) were compared with the situation in non-transformed control aspen trees. The transgenics are characterized by reduced shoot growth and an earlier bud break. Their wood formation did not immediately follow bud break and leaf development but occurred after some delay, about the same time as wood formation was initiated in the control trees. Quantitatively, the wood structure of the transgenics and of the non-transformed controls was not significantly different; therefore the dwarfism of the transgenics is very likely due to a reduction in cell number. Atypical formation of latewood led to the assumption that the differentiation of cells is decelerated. Additionally, cells lacked both secondary walls and normal lignification, and discoloration of the wood and the formation of tyloses were conspicuous in all transgenics. In contrast, they did not occur in the non-transformed control aspen trees. The observations are discussed in relation to the widely accepted auxin hypothesis. It is suggested that 35S-rolC transgenic aspen trees may be a useful model to study the regulatory mechanisms of wood formation.