Structures and chemical compounds causing integumentary inhibition of Erythrina corallodendron seeds in Algeria
Structures and chemical compounds causing integumentary inhibition of Erythrina corallodendron seeds in Algeria. – Phyton (Horn, Austria) 60: 161–172, with 4 figures and 1 table.* Erythrina corallodendron belonging to the genus Erythrina and the family Fabaceae is a tree growing in tropical and sub-tropical regions. The tree is mainly grown as an ornamental plant because of its nice orange flowers but is also considered as a medicinal plant. The aim of this study was to determine the causes of the limited germination rate of seeds under natural conditions. Even under favorable conditions (humidity, optimum temperature), a very low percentage of germination can be observed. Considerably higher percentages of germination of 99.5 % and 85.7 % were obtained after decortication and mechanical scarification, respectively. Also, the duration until the seeds germinated was reduced to only one day by both treatments. The integumentary germination inhibition is related to its impermeability, which is the consequence of two factors: the integument structure and the presence of specific compounds. The screening of chemical compounds in the integument revealed pigments as important metabolites, corresponding to polyphenolic compounds that trap oxygen for the embryo. We noticed the presence of a pigment that solubilized in contact with imbibition water: the erythrin (the role during germination is still unclear). The histo-anatomical study of the seed coat of Erythrina corallodendron by light microscopy and scanning electron microscopy revealed that different tissues arranged in layers form the integument. The presence of macrosclereids covered by the palisade at the hilar scar, the osteosclereids surrounding the tracheid bar and the arrangement of the light line enhance the impermeability. This indicates clearly that the integument constitutes a mechanical barrier, which prevents a fast germination of the seeds. In conclusion, our study revealed that E. corallodendron seeds exhibit a germination problem, which constitutes an important adaptive factor for the survival of the species. Despite this constraint, E. corallodendron remains an important species that adapts well to the Algerian climate, and is therefore an important species considered in reforestation programs.