© 2007 Heron Publishing—Victoria, Canada
Zygotic and somatic embryo morphogenesis in Pinus pinaster: comparative histological and histochemical study
Susana Tereso (1), Kurt Zoglauer (2), Ana Milhinhos (1), Célia Miguel (1) and M. Margarida Oliveira (1,3,4)
1. Forest Biotech Lab, ITQB/IBET, Quinta do Marquês, 2784-505 Oeiras, Portugal / 2. Humboldt-Universität zu Berlin, Institut für Biologie, AG Angewandte Botanik, Invalidenstraße 43, D-10115 Berlin, Germany / 3. Universidade de Lisboa, Faculdade de Ciências, Departamento de Biologia Vegetal, Bloco C2 Piso 1, Campo Grande, 1749-016,
Lisboa, Portugal / 4. Corresponding author (mmolive@itqb.unl.pt) / Received May 8, 2006; accepted July 15, 2006; published online February 1, 2007
Summary
We compared morphogenesis and accumulation of storage proteins and starch in Pinus pinaster Ait. zygotic embryos with those in somatic embryos grown with different carbohydrate sources. The maturation medium for somatic
embryos included 80 µM abscisic acid (ABA), 9 g l–1 gellam gum and either glucose, sucrose or maltose at 44, 88, 175 or 263 mM in the presence or absence of 6% (w/v) polyethylene
glycol (PEG) 4000 MW. Maturation medium containing 44 or 88 mM of a carbohydrate source produced only one or no cotyledonary
somatic embryos per 0.6 g fresh mass of culture. The addition of PEG to the basal maturation medium resulted in a low yield
of cotyledonary somatic embryos that generally showed incomplete development and anatomical abnormalities such as large intercellular
spaces and large vacuoles. High concentrations of maltose also induced large intercellular spaces in the somatic embryonic
cells, and 263 mM sucrose produced fewer and less developed cotyledonary somatic embryos compared with 175 mM sucrose, indicating
that the effect of carbohydrate source is partially osmotic. Zygotic embryos had a lower dry mass than somatic embryos at
the same stage of development. Starch granules followed a similar accumulation pattern in zygotic and somatic embryos. A low
starch content was found in cotyledonary zygotic embryos and in somatic embryos developed in the presence of 175 mM maltose
or 263 mM glucose. In zygotic embryos and in PEG-treated somatic embryos, protein bodies appeared later and were smaller and
fewer than in well-developed somatic embryos grown without PEG. We propose that storage protein concentration might be a marker
of embryo quality.
Keywords:
carbohydrates, maritime pine, maturation, polyethylene glycol, starch, storage proteins.
