FREE AMINO ACIDS IN THE DEVELOPING ENDOSPERM OF MAIZE

Abstract

UNDERSTANDING the metabolism of the developing maize endosperm is a problem of practical and theoretical importance. Carbohydrate metabolism in the maize endosperm has been investigated extensively by means of various biochemical and genetic techniques (Culpepper and Magoon, 1924, 1927; Bernstein, 1943; Sprague et aL, 1943; Andrew et al., 1944; Cameron, 1947; Kramer and Whistler, 1949), but nitrogen metabolism of the endosperm has remained relatively unexplored. Zeleny (1935) and Watson (1949) have shown that endosperm proteins (largely zein and glutelin) are synthesized during the entire kernel maturation period, but that most of the glutelin (alkali-soluble) proteins are synthesized during the first half, and most of the zein complex of proteins (alcohol-soluble) during the last half of the endosperm maturation period. Biochemical genetics studies (Showalter and Carr, 1922; Frey et al., 1949; Frey, 1951) and analyses of various varieties and genotypes of maize endosperm (Hansen et al., 1945) show that there is a direct correlation between the content of zein and of total protein in the endosperm; this mav indicate that alcohol-soluble proteins are the major storage proteins of the endosperm. Interrelations of tryptophan, niacin and indoleacetic acid in the developing maize endosperm have been investigated by Stehsel and Wildman (1950). Their studies are perhaps the first attempt to explore the nitrogen metabolism of the developing maize endosperm on the level of individual enzymesubstrate-product reactions. It is only on this level that one can investigate adequately the various metabolic processes of the developing endosperm. Thus, a working knowledge of the kinds and amounts of nitrogenous components in the endosperm throughout its development is fundamental to understanding endosperm protein synthesis. This study is a preliminary investigation of the free amino acids and amides of the developing endosperm of four varieties of corn. Partition paper chromatography, an analytical technique proven to be useful for rapid surveys of kinds and approximate amounts of amino acids in other plant tissues (Dent et al., 1947) has been adapted for use in this investigation. MATERIALS AND METHODS.-Four morphologically dissimilar varieties of maize: Longfellow Flint,