Histology of organogenic and embryogenic responses in cotyledons of somatic embryos of Quercus suber L.

In cork oak (Quercus suber L.), recurrent embryogenesis is produced in vitr o through autoembryony without exogenous plant growth regulators (PGRs); se condary embryos appear on the embryo axis but seldom on cotyledons. Focusin g mainly on the histological origin of neoformations, we investigated the i nfluence of the embryo axis and exogenous PGRs on the embryogenic potential of somatic embryo cotyledons. Isolated cotyledons of somatic embryos becam e necrotic when cultured on PGR-free medium but gave secondary embryos when cultured on media containing benzyladenine and naphthaleneacetic acid. Cot yledons of cork oak somatic embryos are competent to give embryogenic respo nses. Isolated cotyledons without a petiole showed a lower percentage of em bryogenic response than did those with a petiole. In petioles, somatic embr yos arose from inner parenchyma tissues following a multicellular budding p attern. Joined to the embryo axis, cotyledons did not show morphogenic resp onses when cultured on PGR-free medium but revealed budlike and phylloid fo rmations when cultured on medium with PGRs. The different morphogenic behav ior displayed by somatic cotyledons indicates an influence of the embryo ax is and indicates a relationship between organogenic and embryogenic regener ation pathways.