Co-culture with Daucus carota somatic embryos reveals high 2,4-D uptake and release rates of Arabidopsis thaliana cultured cells

Abstract

By means of co-culture in growth regulator-free medium we analysed whether factors secreted into the medium of Daucus carota (carrot) somatic embryo cultures would be able to overcome the developmental arrest of globular Arabidopsis thaliana somatic embryos. Instead of Arabidopsis embryogenesis being promoted the development of carrot somatic embryos was inhibited at the globular stage in the presence of Arabidopsis suspension culture aggregates with attached globular embryos. Several experiments showed that this was due to the release of previously accumulated 2,4-D by the Arabidopsis cultures. (1) In addition to arresting carrot embryogenesis, co-culture with Arabidopsis cell suspensions also induced callus formation on Arabidopsis root segments. (2) Both effects only occurred with Arabidopsis suspensions grown in the presence of 2,4-D and not with those grown in the presence of NAA, demonstrating that Arabidopsis is not segregating a “general” inhibiting factor. (3) Both effects could be prevented by either binding 2,4-D to active charcoal or by washing it away by changing the medium daily. (4) Uptake of 2,4-D into Arabidopsis cells during culture in 2,4-D containing medium and subsequent release of 2,4-D after transfer to growth regulator-free medium was measured. (5) These low levels of released 2,4-D (0.2– 0.5 μm) could mimic the observed effects. Taken together these data suggest that the high intracellular 2,4-D content of Arabidopsis cultures may interfere with Arabidopsis somatic embryo development beyond the globular stage.