Nitrogen compounds in embryogenie and non-embryogenic calluses of Medicago arborea L

Nitrogen (N) metabolism during embryogenesis may be fundamental in the embryogénie response. We used different expiants of Medicago arbórea L. subsp. arbórea seedlings: cotyledons, petioles and leaves, which form calluses with different embryogénie responses. The endogenous contents of total nitrogen, nitrate, nitrite and ammonia and nitrate reductase activity were determined in embryogénie and non-embryogenic calluses induced from the different expiants. The endogenous total N content decreased in the calluses as the culture time progressed, this decrease being more pronounced in the more embryogénie calluses obtained from petioles with the H8 and F0 media. Inorganic N decreased during embryogenesis, coinciding with an increase in organic N. Thus, N metabolism somehow seems to be essential in embryogenesis. The N detected in calluses, at the start of culture, was mainly metabolised to nitrite. This metabolism was very pronounced; especially in embryogénie calluses obtained from cotyledons and petioles. That is, the metabolism of N seemed to be more marked in the calluses in which embryogenesis was greater. The nitrite content decreased in all the calluses, the contents being lower, especially in the last months of culture, in the more embryogénie calluses obtained from petioles. In many calluses, ammonia levels did not follow any general pattern. Neither was it possible to detect changes in ammonia levels between the embryogénie and non-embryogenic calluses. Regarding nitrate reductase activity, no clear differences between embryogénie and non-embryogenic calluses were found.