Growth and Development of Horticultural Crops (1+1)

Endosperm development and composition

• Regardless of its origin and chromosome number, the endosperm serves a very special function in nourishing the embryo during early seed formation and maturation and later during seed germination before the embryo develops into an independent plant.
• Endosperm tissue is composed of cells with three chromosome sets (3n), two from the maternal and one from the paternal parent. This is the situation encountered in many plants, but in the gymnosperms, such as pine and hemlock, the functional equivalent of the angiosperm endosperm has a different chromosome complement and is derived from the female gametophyte, which is composed of haploid (1n) cells.
  
• In angiosperms where the endosperm is commonly in the triploid (3n) condition, the development of the endosperm generally precedes the development of the zygote.
  
• That is, even though the fusion of the egg and sperm nuclei form the zygote (2n) and the fusion of the sperm nucleus with the polar nuclei form the endosperm nucleus which may occur simultaneously, the 3n endosperm nucleus usually divides to form numerous nuclei before the zygote begins to divide.
  
• Frequently the endosperm develops in the free nuclear condition without forming cell wall materials so that a liquid endosperm containing many free nuclei results. Coconut milk is an example of such a liquid endosperms during the early stages of seed development.
  
• Probably the endosperm of many other plants passes through a similar free-cell liquid stage. During later stages of endosperm development, cell walls form and a cellular, or solid, endosperm is produced.
  
• In many dicotyledonous plants the endosperm is absorbed by the cotyledons of the developing embryo. The food reserves of the cotyledons serves as a nutrient source during germination.
  
• In other plants, particularly monocots (maize, wheat, etc), the solid endosperm persists and becomes a part of the seed, where it functions to nourish the developing embryo during seed germination.