27. High lysine mutant of rice

T. KUMAMARU1, H. SATO2 and H. SATOH3

1) Japan Tobacco Inc., Higashi-shinagawa, Shinagawa-ku, Tokyo, 140 Japan

2) Zennoh Agric. Technical Center, 5-5-1 Higashi-yahata, Hiratsuka, Kanagawa-ken, 254 Japan

3) Genetic Resource Res. Center, Faculty of Agric., Kyushu University, Hakozaki, Fukuoka, 812 Japan

For the purpose of improving the nutritional value of rice endosperm, we need to increase the content of lysine and threonine at the amino acid level. Schaeffer and Sharpe (1987) reported the high lysine mutants selected from cultured cells by cell selection. The N-methyl-N-nitrosourea (MNU) induction method developed by Satoh and Omura (1979) induces many kinds of mutants in high frequencies. Therefore, it may be possible to induce mutants for altered amino acid content by MNU treatment. We searched for amino acid mutants in mutagenised materials.

We screened about 360 endosperm mutants lines (EM lines), which were mutagenised by treating fertilized egg cells in rice cultivars, Kinmaze and Taichung 65. The total amino acids extracted from the rice grain powder of each line were analyzed by the high performance liquid chromatography system using the amino acid analysis column.

As the result of screening, we could select 12 high lysine mutant lines. The 

Table 1. Lysine and histidine contents in high lysine lines and original
strains
===============================================================================
                                        Amino Acid Content (%)
                                     =======================================
Line                                    Lysine      Histidine
===============================================================================
EM 109                                  5.42(0.04)  3.77(0.85)
EM 137                                  5.58(1.86)  3.94(1.07)
EM 139                                  5.44(0.60)  3.91(1.84)
EM 143                                  5.76(1.06)  4.04(0.66)
EM 246                                  5.42(0.52)  3.94(0.57)
EM 253                                  5.14(0.17)  4.10(0.76)
EM 279                                  5.19(0.29)  4.19(0.69)
EM 280                                  5.65(0.29)  3.93(1.25)
EM 317                                  6.38(1.44)  4.32(1.97)
EM 392                                  5.10(0.27)  4.38(0.95)
Kinmaze                                 4.23(0.44)  1.03(1.22)
EM 579                                  5.67(0.08)  4.00(0.67)
EM 596                                  5.24(0.39)  3.17(0.10)
Taichung 65                             4.01(0.35)  1.21(0.13)
==============================================================================
The values shown in parentheses stand for the standard values.  The original
variety of EM 579 and EM 596 is Taichung 65, while that of the others is
Kinmaze.
lysine contents of the original varieties and the high lysine lines are shown in Table 1. The lysine content in the high lysine mutants was 5.10%-6.8%, while those of Kinmaze and Taichung 65, were 4.23% and 4.10%, respectively. The histidine content in high lysine lines was 3.17%-4.30%, while it was 1.30% and 1.21% in Kinmaze and Taichung 65, respectively (Table 1). The resolution of the relationship between high lysine and high histidine needs to be investigated. However, we could obtain no high threonine mutants from the materials investigated. Probably, like other amino acids, the EM lines had almost the same content of threonine as of the original cultivars.

The endosperms of all the high-lysine mutant lines were mostly of floury appearance. The genetic relationship between lysine content and floury endosperm was investigated in the cross between Kinmaze and EM-317. The F2 and parental seeds were analyzed for amino acid content on a single grain basis.

In F2, the normal and floury seeds were 62 and 21, respectively. The mode of segregation gave a good fit to the 3: 1 ratio. Fig. 1 shows the results of the amino acid analysis. In normal seeds, the lysine content varied from 5.60% to 7.40% with a mean of 6.29%. In floury seeds, the lysine content varied from 7.10% to 9.32% with a mean of 8.24%. The lysine content of Kinmaze and EM-317 was 5.56% and 7.99%, respectively. These results suggest that the high lysine content and floury endosperm in EM-317 are the result of pleiotropic gene action.


Fig. 1. Distribution of lysine contents in the F2 seeds from Kinmaze x EM-317.

References

Satoh, H. and T. Omura, 1979. Induction of mutation by the treatment of fertilized egg cell with N-methyl-N-nitrosourea in rice. J. Fac. Agr., Kyushu Univ. 24: 165-174.

Shaeffer, G. W. and F. T. Sharpe, 1987. Increased lysine and seed storage protein in rice plants recovered from calli selected with inhibitory levels of lysine plus threonine and S-(amino-ethyl)cystein. Plant Physiol. 84: 509-515.