A split pollination was used to produce normal (Su su su O2 o2 o2) and high lysine double mutant sugary opaque-2 (su su su o2 o2 o2) endosperms on the same ear of sugary opaque-2 maize plants. Amino acids were determined in the vascular sap of the ear peduncle. Lysine content in the sap was compared with lysine stored in both normal and sugary opaque-2 endosperm during kernel filling. Lysine content in the ear peduncle sap could account for all lysine found in both endosperms. Preformed lysine is highly catabolized in the normal endosperm, but not in the high lysine sugary opaque-2 endosperm. The rate of lysine breakdown appears to be an important mechanism by which the high lysine mutant controls lysine level in maize endosperm. © 1979.181118031805Mertz, Bates, Nelson, (1964) Science, 145, p. 279Mossé, Alcohol-soluble proteins of cereal grains. (1966) Fed Proc, 25, p. 1663Paulis, James, Wall, (1969) J. Agric. Food. Chem., 17, p. 1301Sodek, Wilson, (1971) J. Agric. Food. Chem., 19, p. 1144Sodek, Wilson, (1970) Arch. Biochem. Biophys., 140, p. 29Brandt, (1975) FEBS Letters, 52, p. 288Lawrence, Grant, (1964) Arch. Biochem. Biophys., 104, p. 73Arruda, Silva, (1979) Phytochemistry, 18, p. 409Sodek, (1976) Phytochemistry, 15, p. 1903Silva, Teixeira, Arruda, Lovato, (1978) Maydica, 23, p. 129Pate, Sharkey, Lewis, (1974) Planta, 120, p. 229Pate, Sharkey, Lewis, (1975) Planta, 122, p. 11McCready, Ducay, Gauger, (1974) J. Am. Oil Chem. Soc., 57, p. 336Gallo, Lott, (1965) Bragantia, 24, p. 3Gerhke, Wall, Absheer, (1973) J. Am. Oil Chem. Soc., 56, p. 1096Moore, Spackman, Stein, Chromatography of Amino Acids on Sulfonated Polystyrene Resins. An Improved System (1958) Analytical Chemistry, 30, p. 1185