Light Requirement forShootRegeneration inHorseradish Hairy Roots

Hairy roots ofhorseradish (Armoracia rusticana) wereinduced byinoculation withAgrobacterium rhizogenes harboring Riplas- midandcultured onphytohormone-free Murashige andSkoog medium after eliminating thebacteria. Hairy roots grewvigorously andsometimes formed yellowish calli under darkconditions. On theother hand, growth ofhairy roots stopped after several weeks ofculture withlight, thenshoots wereregenerated. Frequency of shoot formation fromhairy roots increased astheculture period inlight lengthened andthelight intensity increased. Theshoot regeneration wasinduced bytreatment withwhite orredlight, but notwith far-red light. Shoot regeneration byredlight wasinhibited byfollowing treatment withfar-red light. Redandfar-red light reversibly affected shoot regeneration. Excised roots ofnontrans- formed plants grewquite slowly onphytohormone-free Murashige andSkoogmediumandoccasionally formed shoots underwhite light conditions.