Polyembryony

Presence of more than one embryo within a single seed is called polyembryony.

Polyembryony is the occurrence of more than one embryo within a single seed (ovule).

Normally, a seed contains only one embryo formed from the fertilised egg (zygote). In polyembryony, multiple embryos develop within the same ovule - though in most plants only one embryo survives to maturity while the rest degenerate during seed development.

Polyembryony is classified under two systems used across different boards:

System A: True vs. False Polyembryony:

System B: Four Types in Angiosperms:

Origin from Embryo Sac Cells (Other Than Egg):

Embryos can also form from cells within the embryo sac other than the egg cell itself:

1. After fertilisation, the zygotic embryo begins to develop normally.
2. Simultaneously, nucellar cells surrounding the embryo sac begin to proliferate (divide rapidly).
3. These dividing cells protrude into the embryo sac and develop into additional embryos, called nucellar or adventive embryos.
4. Each ovule may contain one zygotic embryo and several nucellar embryos.
5. During seed development, usually only one embryo survives (typically the nucellar one, which is more vigorous); the rest degenerate.

• Polyembryony is the formation of more than one embryo in a single seed, leading to multiple seedlings.
• It was first observed by Leeuwenhoek in Citrus (orange) seeds.
• Polyembryony can occur due to development from the zygote or other tissues like the nucellus and integuments.
• Types include true polyembryony (embryos in the same embryo sac) and false polyembryony (embryos in different embryo sacs).
• Cleavage polyembryony occurs when the zygote splits into many parts, while adventive polyembryony occurs from nucellus or integument cells.
• It is important in horticulture and increases chances of survival by producing multiple seedlings.