Describe Endosperm formation and its function



Development of endosperm begins before that of embryo. It arises from the primary endosperm nucleus (also known as triple fusion nucleus) formed as a result of triple fusion of three nuclei i.e. two polar nuclei and a male nucleus. Primary endosperm nucleus is triploid (3N). It undergoes a series of divisions resulting in the formation of many free nuclei lying within the embryo sac. A vacuole appears in the centre so that the nuclei are pushed to the periphery. Later on unless the endosperm is absorbed by the embryo in free nuclear stage, wall formation takes place starting from the periphery towards the centre of embryo sac and by further centripetal growth, the embryo sac is filled with a compact cellular tissue around the embryo without any intercellular spaces. This tissue is endosperm occasionally as in coconut a vacuole persists in the centre of the embryo sac as it is not completely filled by the endospermic tissue. This type of endosperm development since it involves the process of free nuclear division is called the nuclear type e.g. Fritillaria biflora. This is the most common method of endosperm development. In some plants as in Silphium Lacimatum, each division of the primary endosperm nucleus is followed by wall formation, so that the endosperm is formed at once. This type of endosperm development is known as cellular type.

In some groups endosperm may develop as a few free nuclei only so that it may be regarded as suppressed as in Helobiales and orchids. Several members of Sympetalae a few families of Archichlamydae and monocotyledons show prominent endospmeric loustoria which form very efficient absorptive system.

Function of endosperm:

Endosperm serves as storage tissue as its cells are laden up with food material absorbed through the placenta. The reserve food is stored in large quantities in its cells. This may be deposited as hemi cellulose on the cell walls, when often become very thick as in date and so called vegetable ivory. In most of monocots and some dicots (e.g. castor, butter cup, cotton and all grasses) endosperm persists as permanent tissue in the seed. Such seeds are called albuminous or endospermic.

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