What is somatic embryogenesis?

Oxford dic­tio­nary describes “somat­ic” as “relat­ing to the body, espe­cial­ly as dis­tinct from the mind.”, how­ev­er adding that in biol­o­gy it means “relat­ing to the soma”. The soma is all parts of an organ­ism except for repro­duc­tive cells. In oth­er words: all cells that are dif­fer­en­ti­at­ed and part of an organ or tis­sue type etc. can be called somat­ic cells. Non-somat­ic cells are for exam­ple stem cells.

Embryo­ge­n­e­sis describes the for­ma­tion and devel­op­ment of an embryo. It is impor­tant to know that not only ani­mals have embryos but plants have those as well. 

The term totipo­ten­cy describes the abil­i­ty of (most) plants to form a com­plete organ­ism from somat­ic cells giv­en the right con­di­tions. These con­di­tions can be pro­duced in vit­ro by offer­ing cul­ture media con­tain­ing plants hor­mones, also called plant growth reg­u­la­tors (PGRs). Many plant species have the poten­tial to form organs (roots / shoots) and there­upon to regen­er­ate com­plete plants out of sin­gle plant cells or tis­sue frag­ments using a devel­op­men­tal path­way called organo­gen­e­sis. In somat­ic embryo­ge­n­e­sis how­ev­er, a somat­ic cell is induced in vit­ro to adopt embryo­genic prop­er­ties. This arti­fi­cial process is the only way to prop­a­gate most conifer species efficiently.

The gen­er­a­tion of a cell cul­ture with embryo­genic com­pe­tence is called ini­ti­a­tion. The result­ing embryo­genic cell cul­ture (clone) con­tains ear­ly embryos and can be prop­a­gat­ed on media. The main­te­nance and mul­ti­pli­ca­tion of cul­tures is called pro­lif­er­a­tion. The fresh mass must peri­od­i­cal­ly be placed on new nutri­tion medi­um; alter­na­tive­ly, it is pos­si­ble to store the clone in liq­uid nitro­gen. The next step in somat­ic embryo­ge­n­e­sis is called mat­u­ra­tion. Dur­ing mat­u­ra­tion the ear­ly embryos grow and devel­op into mature, cotyle­donary embryos. To pro­duce emblings (i.e. somat­ic seedlings), mature embryos can be placed on ger­mi­na­tion media under grow lights. Ger­mi­na­tion is the last in vit­ro step and still per­formed under ster­ile con­di­tions. Dur­ing acclima­ti­za­tion, seedlings are placed in soil and slow­ly accus­tomed to ex vit­ro conditions.

Somat­ic embryo­ge­n­e­sis is an impor­tant tool in plant genet­ics and forestry, as it is pos­si­ble to gen­er­ate large num­bers of embryos and thus plants from a sin­gle cell. This is par­tic­u­lar­ly use­ful for plants where nat­u­ral­ly obtained seeds are lim­it­ed. Fur­ther­more, this sys­tem allows us to close­ly mon­i­tor ear­ly plant devel­op­ment and long term stud­ies on the same genet­ic mate­r­i­al, as plants derived from the same ini­ti­a­tion explant and posi­tion are con­sid­ered clones.