Involvement of phytohormones in light-induced adventitious shoot formation of horseradish hairy roots

Abstract

Horseradish ( Armoracia rusticana) hairy roots were treated with auxins or cytokinins to examine the effects on adventitious shoot formation. Naphtalene-1-acetic acid (NAA) and 5,6-dichloro-indole-3-acetic acid (5,6-Cl 2-IAA) suppressed shoot formation under light conditions, but indole-3-acetic acid (IAA) did not inhibit it even at high concentrations. Cytokinins such as N 6-benzyladenine (BA), kinetin (Kin), t-zeatin, N 6- δ 2-isopentenyladenine (i 6Ade) and N 6- δ 2-isopentenyladenosine (i 6Ado) induced shoot formation under dark conditions and enhanced the number of shoots under light conditions. Anticytokinins such as 4-substituted-2-methylpyrrolo[2,3- d]pyrimidine with p-isopropylphenyl ( pPP), p-bromophenyl ( pBP), p-chlorophenyl ( pCP) and s-butyl ( sB), partially inhibited shoot formation in light. Inhibition was overcome by co-applications of BA with the anticytokinins. These results indicate that, in horseradish hairy roots, light irradiation may result in an increase of the endogenous level of cytokinins thus leading to adventitious shoot formation.