The role of proline in thidiazuron-induced somatic embryogenesis of peanut

Peanut seeds germinated on media supplemented with thidiazuron [TDZ: N-phen yl-N'-(1,2,3-thiadiazol-yl)urea], formed somatic embryos at the hypocotyled onary notch region by Day 35 of the culture period. Supplementation of the culture media with proline. thioproline, or glutamine reduced the total num ber of embryos formed, but the resulting embryos were larger, greener and h ad a more synchronous development than the regenerants formed on media cont aining TDZ alone. Analysis of the endogenous amino acid content of the germ inating seeds during the induction phase of somatic embryogenesis revealed accumulation of proline to 6% of the dry seed weight. Concurrent with the e mergence of the radicle, the proline concentration remained significantly e levated throughout the expression phase of embryogenesis. Several other ami no acids including alanine, aspartate, asparagine, glutamate, glutamine, ga mma-aminobutyrate (GABA), hydroxyproline, isoleucine, threonine and valine accumulated to peak values approximately 10-fold higher than those of the c ontrols. These results indicate that proline plays a key role in directing the route of TDZ-induced somatic embryogenesis and that TDZ effectively sti mulates a cascade of metabolic events resulting in the production of specif ic metabolites, including amino acids, required for the regenerative proces s.