Hormonal Relations of the Developing Embryo

Biochemical ontogeny is very striking in the developing embryo. Some essential substance(s) are produced in the suspensor that are exported to the young embryo. This can be easily demonstrated since removal of the suspensor, up to the heart-shaped stage results in cessation of embryo development. Sometime later the embryo becomes more self-sufficient (Cionini et al. 1976, Yeung and Sussex 1979). One of the deficiencies is in GA3 production (Yeung and Sussex 1979). 

It is assumed that lAA plays an important role in the very early stages of embryo development because in the complete absence of lAA there is abnormal embryo development (Haccius 1965). In the young seed the main source would be the developing endosperm and the suspensor. As the embryo matures auxin declines to very low levels (Eeuwens and Schwabe 1975). However, the amount of bound auxin greatly increases (Cohen and Bandurski 1982) in the endosperm. 

A multiple role is apparently played by ABA during growth of the seed. Throughout the growth period of the embryo the concentration of ABA is low (King 1976, Quebedeaux etal. 1976, Hsu 1979, Choinski etal. 1981), but as the embryo matures there is a rapid increase in amount. The increase is correlated with the synthesis and storage of food reserves (Choinski et al. 

For example, vicilin production is stimulated in in vitro cultures of Pha-seolus embryos in the presence of ABA (Rubenstein et al. 1978). Furthermore, in some instances there is a correlation between the amount of ABA and the cessation of embryo growth in the maturing seed. 

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