| Embryogenesis is a key process to plant development and reproduction. The carrot somatic system is a valuable tool in the study of embryogenesis because it can be performed on a large scale in the controlled environment of tissue culture. Auxin is central to the process because the addition of auxin induces callus proliferation and the removal of auxin leads to the formation of somatic embryos. However, what remains unclear is how these auxin manipulations are related to the metabolism of auxin within the tissue and how they are related to the natural process of zygotic embryogenesis.;In order to examine the relationship between the metabolism of exogenous auxin and endogenous auxin, excised hypocotyls were cultured in the presence of 10 ;In order to compare IAA concentrations in zygotic and somatic embryogenesis, a microtechnique to measure IAA in milligram-amounts of fresh weight plant tissue was developed. Fertilization caused a 20-fold increase in the IAA concentration of the ovary, ovule and the developing globular embryo, which seemed to be necessary for cell proliferation. The dramatically elevated free IAA concentrations of the developing globular embryo (2000 pg/mg f.w.) were followed by a 90-fold decrease during the development of the later torpedo stages. This decrease in IAA coincided with the polarized growth of the embryo which is thought to require an auxin gradient. The changes in auxin levels during zygotic embryogenesis paralleled those found previously for somatic embryogenesis, suggesting a similar role for IAA in both somatic and zygotic embryogenesis. |
