Selection of 5-methyltryptophan resistant rice mutants from irradiated calli derived from embryos

For increasing the contents of specific free amino acids in rice (Oryza sativa L.) cultivar, Donganbyeo, mutant cell lines resistant to growth inhibition by 5-methyltryptophan (5MT) were selected from embryo cultured callus irradiated with 50 Gy of gamma rays. Two lines, M₂-1 and M₂-2, were obtained from the regenerated plants by selfing. The segregation ratios of resistance and sensitivity in these lines fitted 9:7 and 3:1 ratios, respectively. Considering the agronomic traits, M₂-1 was about the same as the original variety in culm length and a little longer or higher in panicle length and number of tillers. However, the fertility of M ₂-1 significantly increased compared to the original variety. M ₂-2 had an extremely high culm length and tillering capacity. Four 5MT-resistant homozygous M₃lines (MR classes), M₃-1-40 and M₃-1-116 from M₂-1 (MR 1), and M₃-2-8 and M₃-2-12 from M₂-2 (MR II), were obtained in the same manner as with the M₂ generation. Protein contents of brown rice were increased about 19% and 32% and the total contents of 9 free essential amino acids were 71% and 34% greater than the original variety in the MR I and MR II groups, respectively. However, for the free essential amino acids of polished rice, there was no difference from the original variety.