Culture types, micropropagation and synthetic seeds

Tissue culture comes in several forms:

• Organ culture: growing whole organs such as roots, anthers, ovaries, embryos, endosperm or seeds.
• Callus culture: growing an unorganised mass of cells. It is used to regenerate plants and to introduce genes.
• Cell suspension culture: growing single cells or small clumps in a liquid medium. It is used for gene transfer, to make secondary metabolites, or to produce somatic embryos.

Micropropagation multiplies plants without sex or seeds, so every plant produced is a clone, genetically identical to its parent. Old ways of propagating without seeds (cuttings, grafting, tubers) are slow and depend on the weather. Micropropagation is fast, needs little space, and does not depend on the season.

It is ideal for plants that are non-fertile, rare or endangered, or elite (with especially good qualities): potato, banana, carnation and chrysanthemum. Banana is a major tissue-culture crop in India, providing disease-free planting material; more than 400 million plantlets are produced each year.

Synthetic seeds (artificial or somatic seeds) are somatic embryos from callus, wrapped in a gel such as calcium alginate, together with nutrients and growth regulators, so that they behave like real seeds. They can be stored for long periods, and allow rapid mass propagation of elite plants, hybrids, and plants that are normally propagated without seeds: carrot, grapes, sandalwood.