A 5-methyltryptophan resistant rice mutant, MTR1, selected in tissue culture

Cell lines resistant to tryptophan analogue 5-methyltryptophan (5MT) were selected in seed-derived calli of Oryza sativa L. var. 'Norin 8'. Plants were regenerated (R1 from one selected callus line (MTR1). In three out of the six R1 plants, 5MT resistance was inherited in the R2 and R3 generations as a dominant nuclear mutation. Segregation ratios in the progeny of heterozygous plants were 1∶1. Morphological and fertility variation seen in some of the R2 plants were not correlated with 5-methyltryptophan resistance. Resistance in the MTR1 callus was due to the accumulation of high levels of free tryptophan (87-fold) that was associated with an increase in free phenylalanine content (9-fold). The leaves of resistant plants also contained elevated levels of free tryptophan and phenylalanine.