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.
============================================================================= Code number Type Origin Px-1 -------------------------------------- zymogram genotype ============================================================================= 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 =============================================================================
a: Taiwan Agricultural Research Institute, Taichung, Taiwan
b: National Institue of Genetics, Misima, Sizouka-ken, Japan
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.