The nutritional quality of cereals, including rice, would be improved by increasing the lysine content. Experiments were designed to test whether cell lines and plants could be recovered from in vitro selections. Mutants of rice recovered from inhibitory levels of lysine plus threonine and S(2-aminoethyl)cysteine from anther-derived calli were regenerated and characterized at the whole plant, cell, and enzyme level. These procedures produced plants with 15% higher lysine in milled grains than the starting cultivar and provide excellent materials for basic studies in cell selections, lysine biochemistry, stress-related biochemistry and gene isolations. A tissue culture line is now available that exports protein more efficiently than the wild type cells and provides materials for the study of mechanisms of expression of the recessive gene(s) conditioning the enhanced lysine phenotype.