Shoot apex explants for induction of somatic embryogenesis in mature Quercus robur L. trees |
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Authors: | M C San-José E Corredoira M T Martínez N Vidal S Valladares R Mallón A M Vieitez |
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Institution: | 1. Instituto de Investigaciones Agrobiológicas de Galicia, CSIC, Avda. de Vigo s/n, Apartado 122, 15780, Santiago de Compostela, Spain
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Abstract: | A procedure for inducing somatic embryos in shoot apex explants (2 mm) excised from shoot proliferation cultures established
from adult oak trees (Quercus robur) was investigated. Embryogenesis was induced in shoot tip as well as leaf explants in three out of the five genotypes evaluated.
Somatic embryos were formed by culture in induction medium supplemented with 21.48 μM naphthalene acetic acid and 2.22 μM
benzyladenine for 8 weeks, and successive transfer of explants to expression media with a low concentration of growth regulators
and without them. Both types of explants formed callus tissue from which somatic embryos developed, indicating indirect embryogenesis.
Although the embryogenic frequencies were lower than 12%, it did not prevent the establishment of clonal embryogenic lines
maintained by repetitive embryogenesis. Histological study confirmed an indirect somatic embryogenesis process from shoot
tip explants, in which leaf primordia and the corresponding axial zones were involved in generating callus, whereas the apical
meristem itself did not proliferate. The origin of embryogenic cells appeared to be associated with dedifferentiation of certain
parenchymal cells in callus regions after transfer of explants to expression media without auxin. Division of embryogenic
cells gave rise to proembryo aggregates of unicellular origin, although a multicellular origin from bulging embryogenic areas
would also seem possible. Further development led to the formation of cotyledonary-stage somatic embryos and nodular embryogenic
structures that may be considered as anomalous embryos with no clear bipolarity. Inducement of somatic embryos from explants
isolated from shoot cultures ensures plant material all year round, thus providing a significant advantage over the use of
leaf explants from field-grown trees. |
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