More than 40 isozyme loci would exist in rice, but the chromosomal location is
known for Est-2, Amp-3 and Pgi-2 only, all being located on Nishimura's
chromosome 6 (Linkage group I; Nakaghra and Hayashi 1976; Sano and Barbier
1985). To determine the relevant chromosomes of other loci, the trisomic series
of Nipponbare, made available through Dr. N. Iwata of Kyushu Unviversity, were
each crossed with an Indica strain from Vietnam (Oka's tester Ac.001) and a
strain of Asian common wild rice (W628). The trisomic F\1\ plants generally had
a low seed fertility. The plumules of germinating F\2\ seeds were assayed by
starch-gel electrophoresis. So far, F\2\ ratios for 10 isozyme loci were
examined in crosses with 7 trisomics. A significant excess of alleles derived
from the female trisomic parent, expressing a trisomic ratio, was found for
Amp-2 in the F\2\ with trisomic D (trisomy for chromosome 12) and for Pgd-1 in
the F\2\ with trisomic G (chromosome 9). In other crosses, normal ratios or a
deficiency of alleles from the trisomic parent were observed.
The trisomic F\1\ plants from trisomic A (trisomy for chromosome 4)Xa wild rice W1653 had a very low seed fertility. They were crossed with an Indica cultivar (Ac.414) which had, at the Sdh-1 locus, another allele different from either of the two carried by the F\1\ plants. Since Sdh-1 genes produce monomeric enzymes, three allelic bands were observed in the triple heterozygote, indicating that Sdh-1 is located on chromosome 4. It is concluded that Amp-2 is located on Nishimura's chromosome 12 (su linkage group), Pgd-1 on chromosome 9 (linkage group VIII), and Sdh-1 on chromosome 4 (d-33 linkage group).
Table 1. F\2\ ratios for Amp-2 and Pgd-1 in crosses with different trisomic
lines
References
Nakagahra, M. and K. Hayashi, 1976. Detection of esterase isozyme loci of O. sativa L. Jpn. J. Breed. 26, Supplem. 1: 114-115.
Sano, R. and P. Barbier, 1985. Analysis of five isozyme genes and chromosomal location of Amp-1. RGN 2: 60-62.