Enhanced production and germination of somatic embryos by temporary starvation in tissue cultures of Daucus carota

Embryogenic callus was induced from cotyledonary explants of Daucus carota L. cultured on solidified MS medium supplemented with 1 mg l^-1 2,4-D. Following callus initiation somatic embryos were developed from the callus on MS medium without 2,4-dichlorophenoxyacetic acid. To stimulate the production and germination of somatic embryos we cultured the callus under physically and chemically modified conditions during subculture. When the embryogenic callus was cultured on half-strength MS medium or MS medium without sucrose or cultured under conditions of reduced humidity (69.3%), the production of embryos increased 3.4- to 4.5-fold compared to culture on MS medium containing 3% sucrose (control). Embryogenic callus cultured on MS medium after 5 days of starvation (by being placed in empty 12-well tissue culture plates) showed a 20-fold increase in somatic embryo production and enhanced maturation and germination of embryos. An important point is that the germination of somatic embryos with cup-shaped cotyledons, after a period in culture without medium, was remarkably improved (92%) compared to that of the controls (23%).Thus, we were able to show that stress by starvation without medium led to the enhanced production and increased germination of somatic embryos.