Abstract: Embryogenic callus was induced from PLB ( protocorm-like body) cubes of Phalaenopsis spp. During callus induction, DNA methylation levels in cultures declined continuously and had a very significant negative correlation with the change of H₂O₂content. Supp lemented H₂O₂ in the medium containing lower concentration of growth regulator ( 6-BA) , the induction rate of callus increased, and this indicated that exogenous H₂O₂ could be used to replace part of growth regulator for embryogenic callus induction. The induction rate of embryogenic callus decreased when supp lemented dimethylthiourea, a quencher of H₂O₂, in culture medium. H₂O₂was possibly a signalmolecule thatmediated the induction of embryogenic callus. In callus induction period, SOD activity played an important role in the change of H₂O₂content in cultures

Key words: Phalaenopsis spp., embryogenic callus, H2O2, DNA methylation, antioxidas