For asparagus, a relationship between spear elongation and endogenous substances, including plant hormones, has been suggested(Kojima and Sakurai, 1994; Ku and Woolley, 2006). Furthermore,abnormal O2 conditions are known to induce some morphological changes in plant organs, such as internode elongation, throughthe regulation of plant hormones (Fujii et al., 1974; Voesenek et al.,2003). Therefore, these previous findings suggest that high concentrations of O2 may affect the production, accumulation, or activity of such endogenous substances.