Distribution of [14C] Dichlorophenoxyacetic Acid in Cultured Zygotic Embryos of Zea mays L.

Abstract

The uptake of 2,4-dichlorophenoxyacetic acid (2,4-D), necessary for the in vitro induction of callus formation and somatic embryogenesis in cultured immature maize embryos, was quantified after culture on nutrient medium with [ 14 C]2,4-D. The identity of the 14 C label in the embryos was determined by high performance liquid chromatography (HPLC), and its distribution within embryos was visualized on sections of plastic embedded material. Quantification of the 14 C label after a pulse label of 16 h showed a hundredfold accumulation of 2,4-D in the embryos with respect to the initial medium concentration. During tissue processing for in situ detection of 14 C, however, up to 70% of the label disappeared because of the embedding process. The best structural preservation was obtained after ethanol-mediated infiltration of Technovit 7100. Water-mediated infiltration of Technovit 7100 gave the highest retention of 14 C. HPLC analysis showed that more than 95% of the residual 14 C label found in embryos was still 2,4-D. Autoradiography showed that the embryogenic inbred line A188 contained 14 C label in distinct regions of the scutellum, coleoptile, and suspensor. The nonembryogenic inbred line A632 contained more label after 16 h of culture in a different distribution compared with A188. Subculture of the embryos for 24 and 72 h and histologic analysis showed that cell proliferation and callus formation were restricted to specific regions of the embryo in both inbred lines. The pattern of 2,4-D distribution did not codistribute with regions of proliferation, indicating that 2,4-D is not the only trigger for proliferation.

Reactive oxygen species‐mediated enzymatic systems involved in the oxidative action of 2,4‐dichlorophenoxyacetic acid*

“…At high concentrations, 2,4‐D acts as a herbicide on dicotyledoneous plants, and it has been used for several decades in cereal crops (Aberg & Eliasson 1978; Heering & Peeper 1991; Johnson & Murphy 1991; Sterling & Hall 1997). However, at low concentrations, is broadly used in in vitro plant tissue culture for induction of calli formation and as a somatic embryogenesis stimulating substance due to its similarity to auxins (Bronsema et al . 1998; Kitamiya et al .…”