The various nitrogenous solutes important to embryo development in symbiotic soybean plants were determined during the midpodfilling stage. Glutamine was the principal form of nitrogen, contributing 55% of the embryo nitrogen requirement. Asparagine was the second most important, contributing 20%. The ureides allantoin and allantoic acid directly contributed only insignificantly to the total nitrogen requirement of the embryo. These conclusions were based upon analyses of tissue extracts, translocation studies of radiolabeled solutes, analysis of in vivo seed coat exudate collected from the freespace of attached, surgically altered seeds, and the in vitro culture of isolated immature soybean embryos.
