Some useful mutant varieties by using various screening methods
Rice Although rice is not a high protein grain crop, the protein content is ca. 7% when the white rice is cooked. A mutant line with a low content of gulutelin was obtained from the ethyleneimine (EI) treatment to “Nihonmasari.” The “LGC-1” was developed from back-crossing this mutant with the original “Nihonmasari” to eliminate undesirable characteristics, such as semi-sterility and semi-dwarfism [7]. The seed protein of the “LGC-1” is composed of mainly of a low amount of digestible glutelin and high amount of indigestible prolamine. This construction of protein is disadvantageous for the digestion of rice grains in humans, though the total amount of protein is mostly similar to the original cultivar. As a result, the “LGC-1” is useful as “low protein rice,” and some clinical trials on patients with kidney disease indicate that the variety is a useful and effective daily food for such patients [8]. The defect of the “LGC-1” is its eating quality, and there are the other loci that control the biosynthesis of digestible protein, such as globulin. Therefore, Nishimura, et al . [9] induced a mutant named “89WPKG30-433” with a deficiency in globulin from the leading Japanese cultivar “Koshihikari” through Gamma-ray irradiation. They hybridized it with the “LGC-1” and selected “LGC-Katsu” and “LGC-Jun” from the hybrids, whose globulin content was as low as the “LGC-1,” where the globulin content is zero. The total digestible protein content tested to about 30% of ordinary rice. As the eating quality is highly improved and digestible protein content is lower than “LGC-1,” these two cultivars will greatly help in the dietary management of proteins with chronic renal failure.