An Ultrastructure Study of Tumor Cells of Haworthia Plants Induced by 2,4-D

Abstract

Treatment of normal callus cells of Haworthia variegata with high concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) promoted the development of tumor-type growth. At low concentrations (1 and 2 mg/liter), 2,4-D had little adverse effects on the growth and morphogenesis of the callus, however, in some tubes abnormal-appearing roots were detected. Calli on the media containing 5, 10 and 20 mg/liter of 2,4-D developed pink-brown pigmentation, produced numerous minute nodules, induced tumor-type growth, showed little differentiation and produced abnormal roots and leaves. Ultrastructure studies of auxin-induced tumors in some plants have been made by several investigators, however, no information is available on the fine structure of the 2,4-D induced tumor cells of Haworthia plants. Tissues from tumor and control groups were fixed in 2% osmium tetroxide, post-fixed in 4% glutaraldehyde, and embedded in Epon 812. Sections were cut on a Porter-Blum MT-2 ultramicrotome, stained with uranyl acetate-lead citrate and examined on a Philips Model 201 transmission electron microscope operating at 60 kV.