Vitamins embryo requirements

Lots of seeds are eaten for human nutrition. A seed is the primary reason for which whole plants exist. It is the next generation of plants, since it contains a new plant in the form of an embryo plus stored food to nourish the embryo as it develops. Since the plant embryo requires proper nutrition from the stored food, seeds are good sources of protein, carbohydrate, fat (oil), minerals, and vitamins. 

Poultry do not require vitamin C in their diet because their body tissues can synthesize this vitamin. The other vitamins must be provided in the diet in proper amounts for poultry to grow and reproduce. The egg normally contains sufficient vitamins to supply the needs of the developing embryo. For this reason, eggs are one of the best animal sources of vitamins in the human diet. 

There are a number of media available which are not based on a detailed investigation of growth requirements, but rather include crude mixtures of nutrients added to promote cell growth. These include lactalbumin hydrolysate (Appendix 1 Table 9) or yeast extract (Appendix 4) to provide an inexpensive source of amino acids or vitamins. Thus Melnick s monkey kidney media A and B (Melnick, 1955) contain lactalbumin hydrolysate and calf serum in Hanks and Earle s BSS, respectively. Chick embryo extract and tryptose phosphate broth (Appendix 1, Tables 11 and 12) are also used occasionally and their use is referred to where appropriate throughout the book. Mitsuhashi and Maramorosch mosquito cell medium contains lactalbumin hydrolysate, yeast extract and foetal calf serum in a specially developed saline (Mitsuhashi and Maramorosch, 1964 Singh, 1967). 

The correct level of the active metabolites of vitamin A which control the nuclear receptor signalling pathway is required for appropriate embryonic development. Too much or too little of the receptor ligands is equally harmful for the embryo. It has been well documented that when there is an excess of vitamin A or its metabolites during embryonic development, defects occur in the CNS. An excess of RA causes specific defects of the anterior hindbrain whereby anterior rhombomeres can be lost or respecified to more posterior areas or it can cause poste-riorization of the whole CNS, whereby forebrain structures are lost [36, 50, 86-88]. More recently, Maden et al. describe defects that arise in the central nervous system of quail embryos when they develop in the absence of vitamin A [50]. There are three defects in these embryos (1) the posterior hindbrain is completely missing (2) the neural tube fails to extend neurites out into the periphery (3) the neural crest cells die. 

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