Concentrations of Sucrose and Nitrogenous Compounds in the Apoplast of Developing Soybean Seed Coats and Embryos

Abstract

The apoplast of developing soybean (G. max cv. Hodgson) embryos and seed coats was analyzed for sucrose, amino acids, ureides, nitrate and ammonia. The apoplast concentration of amino acids and nitrate peaked during the most rapid stage of seed filling and declined sharply as the seed attained its maximum dry weight. Amino acids and nitrate accounted for 80-95% of the total N, with allantoin and allantoic acid either absent or present in only very small amounts. Aspartate, asparagine, glutamate, glutamine, serine, alanine and .gamma.-aminobutyric acid were the major amino acids, accounting for over 70% of the total amino acids present. There was a nearly quantitative conversion of glutamine to glutamate between the seed coat and embryo, most likely resulting from the activity of glutamate synthase present in the seed coat tissue. This processing of glutamine suggests a partly symplastic route for solutes moving from the site of phloem unloading in the seed coat to the embryo.