Endosperm Culture

Introduction In flowering plants, nutrition of the embryo is an important and vital aspect of the life cycle. In angiosperms, it is accomplished by the formation of a new structure, the endosperm, produced by a unique event of double fertilization.

Double Fertilization Double fertilization occurs: One sperm nucleus (1n) fertilizes the egg, producing a zygote (2n)  which becomes the plant embryo inside the seed. Another sperm nucleus fuses with the polar nuclei, resulting in a triploid endosperm (3n). Endosperm is a source of food for the young embryo.

Endosperm

History Lampe & Mills (1933) were the first to report the proliferation of immature endosperm tissue of Maize, grown on medium containing extract of potato. La Rue (1947) observed that in nature, in maize , the pericarp ruptured & the endosperm exhibited a white tissue mass.

Endosperm Culture Sehgal (1974) cultured the immature endosperm of Hordeum & Triticum. In organogenesis was successfully induced in culture of immature endosperm of Oryza sativa by Nakano et al. (1975).

Endosperm Culture The age of endosperm at culture is critical for its growth in vitro. In Maize, Wheat & Barley, endosperm tissue younger than 8 or older than 12 days after pollination did not grow in cultures. The endosperm of Cucumis can be grown only when excised 4-7 days after pollination.

Media Requirement The mature endosperm of parasitic taxa shows optimal growth on a medium containing either a cytokinin or a cytokinin & an auxin. In autotrophic members, casein hydrolysate or yeast extract is also essential.

Endosperms of Santalum album, Croton bonplandianum & Ricinus communis could be grown on White’s medium containing 2,4- D, kinetin & yeast extract. Organ formation has been demonstrated mainly in parasitic species (Exocarpus, Taxillus) and in some autotrophic species (Croton, Santalum, Citrus)

Differentiation In all parasitic members - Differentiation of shoot buds or roots without callusing. In autotrophic members - Callus mass followed by differentiation of shoot buds or roots.

Organogenesis in Culture Organogenesis observed only in few species such as Rice, Apple, Citrus, Santalum, Croton, etc. In Ricinus communis, Zea mays & Cucumis mature endosperm proliferation resulted in a callus tissue of unlimited growth but organogenesis did not occur.

Applications Triploid plants can be raised through endosperm culture. Wang & Chang (1978) produced triploid plantlets from Citrus. Laxmi sita et al. (1980) developed triploid plants of Santalum album .

Presently there are number of crop species (banana, apple, beet, tea, mulberry) in which triploids are in commercial use. Endosperm can be used as a nurse tissue for raising hybrid embryos.