14. A modifier gene for peroxidase isozyme in rice

Chiang Pai

Department of Agronomy, National Chung Hsing University, Taichung, Taiwan 400, China

A gene which alters the electrophoretic mobility of peroxidase isozymes specified by the Pox-1 locus was detected in certain varietal crosses. Four alleles, Pox-10c, Pox-12A, Pox-14A, and Pox-1Nul, have so far been known at this locus. The null allele produces no band in homozygotes, but the other three active alleles produce isozymes of dimeric form with different migration rates, i.e., bands 0C, 2A and 4A (Pai et al. 1973). Now, it is presumed that these bands occur at respective normal positions when a dominant modifier gene, Mpx-1, is present. In homozygotes for its recessive allele, mpx-1, the three active alleles produce their bands at positions deviating about 7 mm toward cathod, respectively (Fig.1). Thes modified bands were designated as 0mC, 2mA and 4mA, respectively. The mpx-1 gene was found in a Japonica strain, Peng 117A (Acc.701 at Taiwan Agricultural Research Institute) while the dominant Mpx-1 gene seems to be distributed commonly in many cultivated and wild rice strains. The mutant strain with mpx-1 was crossed with other strains with different Pox-1 alleles (Table 1). Observations of the F1 and F2 plants showed that 1) the modifier is inherited as a Mendelian recessive, 2) it is independent of Pox-1, and 3) peroxidase isozymes specified by genes other than Pox-1 are not affected by the modifier. This is a new type of genic control of isozymes. A similar case has been reported in maize (Newton 1974).

Fig. 1 Diagram showing the positions of peroxidase bands specified by Pox-1 alleles which are modified by mpx-1 and the mode of F2 segregation.

Table 1. Strains used for crosses and their peroxidase isozymes.

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Code number  Type     Origin              Px-1
                                      --------------------------------------
                                       zymogram              genotype
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701       Japonica   Taiwan a          2mA          mpx/mpx Px-12A/Px-12A    
8216      Indica     Indiaa            0C           Mpx/Mpx Px-10C/Px-10C    
9617      Indica     Vietnama          0C           Mpx/Mpx Px-10C/Px-10C    
T65       Japonica   Taiwanb           2A           Mpx/Mpx Px-12A/Px-12A    
108       Indica     Taiwanb           2A           Mpx/Mpx Px-12A/Px-12A    
362       Indica     Taiwana           2A           Mpx/Mpx Px-12A/Px-12A    
W1294     O. perennis Philippinesb     4A           Mpx/Mpx Px-14A/Px-14A    
3008      Japonica   Japana            Null         Mpx/Mpx Px-1Nul/Px-1Nul    
4641      Japonica   Taiwana           Null         Mpx/Mpx Px-1Nul/Px-1Nul    
4650      Japonica   Taiwana           Null         Mpx/Mpx Px-1Nul/Px-1Nul    
9424      Japonica   U.S.A.a           Null         Mpx/Mpx Px-1Nul/Px-1Nul    
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a: Taiwan Agricultural Research Institute, Taichung, Taiwan

b: National Institue of Genetics, Misima, Sizouka-ken, Japan

References

Newton, K.J., 1979. A gene affecting the electrophoretic mobilities of the mitochondrial MDH's is on chromosome 1. Maize Genetics Newsletter 53: 18-19.

Pai, C., T. Endo and H.I. Oka, 1973. Genic analysis for peroxidase isozymes and their organ specificity in Oryza perennis and O. sativa, Can. J. Genet. Cytol. 15: 845-853.