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International Rice Research Institute, P.O. Box 933, Manila, Philippines
Isozymes are important biochemical markers for genetic mapping. In O. sativa, 24 isozyme loci representing 76 alleles have been identified (Glaszmann et al. 1988). Of these, 18 loci have been located on 8 of the 12 rice chromosomes. We continued our survey for polymorphism for additional loci to map the remaining four chromosomes. A set of isozyme marker accessions representing variability for 24 loci previously identified was examined. In this communication, we report polymorphism for four new isozyme loci (Fdp-1, Xdh-1(t), Dia-1(t), Dia-2(t)). These loci are expressed at different developmental stages of the rice plant (Table 1).
Fructose-1,6-diphosphatase (FDP), E.C. 3.1.2.11: Activity was detected in 4-6 day old germinatin seed using starch gel electrophoresis (Glaszmann et al. 1988) and polyacrylamide gel electrophoresis (30%T, 5%C, pH8.8 for the separating gel and 30%T, 2.5%C, pH6.8 for the stacking gel). Zones of enzymatic activity were detected through the procedure described by Shaw and Prasad (1970). The locus Fdp-1 has three variant types corresponding to three alleles including a null. The heterozygotes display three major bands which is typical to a dimeric enzyme (Fig. 1).
Xanthine dehydrogenase (XDH), E.C. 1.2.1.37: Activity was also detected in 4-6 day old germinating seed using polyacrylamide gel electrophoresis. Zones of enzymatic activity were detected using the procedure described by Vallejos (1983). Xdh-l(t) locus has two alleles corresponding to slow and fast moving bands (Fig. 2).
Diaphorase (DIA), E.C. 1.6.4.3: Activity was detected in both the white and green portions of the emerging leaves sampled during early tillering to pre-booting stage. Electrophoresis was performed using the procedure described by Glaszmann et al. (1988). Two distinct patterns were observed suggesting two diaphorase isozyme loci Dia-1(t) and Dia-2(t). Each of the locus consists of two types of mobility, fast and slow, corresponding to two alleles (Fig. 3.).
Crosses of the IR36 primary trisomic series and representative marker
Table 1.Polymorphism for four new isozyme loci in IR36 and other
rice accessions
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Enzyme Isozyme locus Allele Marker accessions
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Fructose-1,6-diphosphatase(FDP) Fdp-1 null 27642,41048
slow 23754,43394,53675
fast 30416*,6245,6274
6304,6434,6538
7755,9104,9158
12880,13835,19906
27748,29040,29726
32301,33153,42469
33888,37901,42469
43400,53642,53950
Xdh-1(t) slow 30416*,6245,6274
Xanthine dehydrogenase (XDH) 6304,6434,6538
7755,9104,9158
12880,13835,19906
23754,27642,27748
29040,29726,32301
33153,33191,33888
37901,41048,42469
43394,43400,53642
53950
fast 33
Diaphorase(DLA) Dia-1(t) slow 27642,33191,53642
fast 30416* 6245,6274
6304,6434,6538
7755,9104,9158
12880,13835,19906
23754,27748,29040
29726,32301,33153
33888,37901,41048
42469,43394,43400
43675,53950
Dia-2(t) slow 30416*,6245,6274
6304,6434,6538
7755,9104,9158
12880,13835,19906
23754,27642,27748
29040,29726,32301
33153,33191,33888
37901,41048,42469
43394,43400,43675
fast 53950
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t: tentative
* IR36 accession number
accession for each of the four isozyme loci have been made. Gene dosage
effect in the F1 and F2/BC1 segregation are being investigated to determine
their location on rice chromosomes.
Fig. 1. Starch gel zymogram and diagrammatic interpretation of
fructose-1,6-diphosphatase (FDP).
Fig. 2. Polyacrylamide gel zymogram and diagrammatic interpretation of
xanthine dehydrogenase (XDH).
Fig. 3. Starch gel zymogram and diagrammatic interpretation of diaphorase
(DIA).
References
Glaszmann, J. C., B. G. delos Reyes and G. S. Khush, 1988. Electrophoretic variation of isozymes in plumules of rice (0. sativa L.)-a key to the identification of 76 alleles at 24 loci. IRRI Research Paper Series, Intl. Rice Res. Inst., P.O. Box 933, Manila, Philippines.
Shaw, C. R. and R. Prasad, 1970. Starch gel electrophoresis of enzymes-A compilation of recipes. Biochem. Genet. 4: 297-320.
Vallejos, C. E., 1983. Enzyme activity staining. In Isozymes in Plant Genetics and Breeding, Part A. Tanksley and Orton eds. p. 469-516.
