Reversible morphology change of horseradish hairy roots cultivated in phytohormone-containing media

Abstract

Horseradish hairy roots were cultivated in the presence of phytohormones to achieve the processes of cell aggregate formation from the hairy roots and hairy root regeneration from the cell aggregates. In the process of cell aggregate formation, the combined addition 1.0 (or 2.0) mg/dm 3 NAA (1-naphthaleneacetic acid) and 0.5 mg/dm 3 BAP (6-benzylaminopurine) caused a significant change in morphology from hairy roots to cell aggregates. On the other hand, the formation and growth of hairy roots in the regeneration process were enhanced in the medium with the addition of NAA only. Effective regeneration of hairy roots from the cell aggregates was obtained in a culture with 2.0 mg/dm 3 NAA, and the number of regenerated roots was 26–38 per cm 2-surface area of cell aggregate. It was found that the respective growth and peroxidase activity of roots repeatedly regenerated over three generations were comparable to those of the original hairy roots. This indicated that the hairy root properties were stably retained, even after a series of the cell aggregate formation and hairy root regeneration processes were conducted.