Question

In a type of apomixis known as adventive embryony, embryos develop directly from the
(a) Nucellus or integuments
(b) Synergids or antipodals in an embryo sac
(c) Accessory embryo sacs in an ovule
(d) Zygote

Answer 1

Hint: In adventive embryony, the embryo develops from either that part which forms the main body of the ovule or from one or two coverings surrounding that main body of ovule. When a pollen tube enters the ovule by piercing this part instead of the micropyle it is known as mesogamy.

Complete answer
Apomixis is a type of asexual reproduction that mimics sexual reproduction but seed formation occurs without fertilization. In the adventive type of polyembryony, embryos develop directly from the nucellus or integuments. Adventive polyembryony is seen in Citrus, Opuntia, and Mangifera.

Additional Information:
- In polyembryony, multiple embryos develop, it was first observed by Leeuwenhoek in the seeds of Citrus.
- The following types of polyembryony are seen in plants:
- Simple Polyembryony: More than one embryo sac is present and therefore more than one oosphere. This type of polyembryony is seen in Brassica.
- Mixed polyembryony: In this case, more than one pollen grains germinate and therefore multiple pollen tubes enter the ovule and fertilize synergids and antipodal cells. This type of polyembryony is seen in Ulmus.
- Cleavage Polyembryony: Here a single embryo splits into multiple embryos and each of them develops individually. This type of polyembryony is seen in Orchids, Nymphaea, and Nicotiana.

So, the correct answer is,” In adventive polyembryony, embryos develop directly from the nucellus or integuments.”

Note:
Polyembryony is of true and false type. It is known as true polyembryony if multiple embryos develop from a single embryo and it is considered as false if the multiple embryos are formed from two different embryo sacs. But this is rarely observed in the angiosperms. It is important to know that an adventive embryo can also develop from the endosperm and this is seen as Balanophora. This method of apomixis is widely used for the production of hybrid seeds as in this process no variations arise and a large number of hybrid seeds can be obtained year after year without depending on hybrids seeds available in the market which are very costly.