Characterization of high-lysine mutants of rice

Rice (Oryza sativa L.) serves as an important source of dietary protein for humans in developing countries. The nutritional quality of rice endosperm storage proteins is not optimal because the proteins are deficient in certa in essential amino acids. Recently, the USDA released five increased lysine germplasm lines. The biochemical basis for the increased lysine content in these mutants is not clearly understood. The objective of this study was t o characterize two of the rice mutants to obtain information on the biochem ical rind anatomical alterations associated with the high-lysine phenotype. Analysis of seed proteins revealed lower levels of 14-kDa prolamins in the mutants 2K497 and 2K539 and a higher amount of a 10-kDa prolamin. Amino ac id analysis of the prolamin fraction also indicated that this group of prot eins contained a higher proportion of lysine. The concentration of elongati on factor 1A(eEF1A) and the binding protein (BiP), two proteins that accumu late in high-lysine mutants of maize (Zea mays L.), were not significantly affected in the high-lysine rice mutants. Microscopic examination revealed that the mutant 2K497 underwent abnormal seed development and contained ver y large starch granules and numerous densely packed protein bodies.