Somatic embryogenesis of holm oak (Quercus ilex L.): ethylene production and polyamine content

The production of ethylene and the endogenous content of polyamines (PAs) have been recorded during the early development, maturation and germination of holm oak (Quercus ilex L.) somatic embryos. Ethylene production was high in embryogenic callus, immature somatic embryos and in explants showing secondary embryogenesis, while it was lower in mature and germinating somatic embryos. A higher ethylene production was also associated to the process of secondary embryogenesis. The exogenous application of 1-amino-1-cyclohexane carboxylic acid was not significantly effective on the production of ethylene by holm oak somatic embryos. Total PAs were more abundant in embryogenic callus and in both somatic and zygotic immature embryos, decreasing later on in the mature and germination phases. Immature somatic embryos of holm oak and immature zygotic embryos contain high levels of spermidine (Spd), which decreased during maturation and germination. Spermine (Spm) concentration was lower than that of Spd. Spm was more abundant in embryogenic callus and immature zygotic embryos than in mature embryos. Ethylene production did not seem to interfere with PA metabolism.