During million years (MY) plants made up an efficient mechanism for their owner protection, neutralizing oxygen radicals (superoxide) in the cell wall. Evaluation of the oxygen paticipation on plant secondary metabolism, especially associated with the lignin formation, suggested two oxidation mechanisms: vertical and horizontal oxidation. The latter is mediated by enzymatic mechanisms, contributing to the structural profile of modern plants. Vertical oxidation is carried out in the cell wall and is responsible by lignin accumulation, while horizontal oxidation is elaborated into the cytoplasmatic compartment. These mechanisms are independent and play an important strategy to prevent destructive oxygen effect on the plant cells.