Relationships between hormonal contents and the organogenic response in Pinus pinea cotyledons

Isolated cotyledons from Pinus pinea L. germinated embryos cultured in vitr o showed shoot organogenesis in response to treatment with 4.4 muM N-6-benz yladenine (BA). In late germination phases, the extent of the response onse t decreased and adventitious buds were redistributed to the basal zone of t he cotyledons. To understand these two events, analyses of indole-3-acetic acid (IAA) and several cytokinins have been carried out in apical and basal portions of cotyledons taken at four different culture periods of the embr yos on germination medium (0, 2, 4 or 6 d). The highest endogenous content of all hormones, except N-6-isopentenyladenosine, was found in the most res ponsive explants, those that were taken from O-d-old cultured embryos. Apic al portions of cotyledons taken from 0 to 4-d-old cultured embryos showed a reduction in the content of IAA and several cytokinins, but basal portions did not show the same pattern. BA dose-response curves were made to explai n the loss of caulogenic potential with the age of the explants. The result s suggested the combination of two factors, changes in the endogenous hormo nal content in original explants and loss of their sensitivity to exogenous ly applied BA, as the cause for the reduction of the ability of Pinus pinea cotyledons to form adventitious buds. (C) 2001 Editions scientifiques et m edicales Elsevier SAS.