G. S. KHUSH, D. S. MULTANI, B. G. de los REYEs and D. S. BRAR
International Rice Research Institute, P.O. Box 933, Manila, Philippines
Isozymes are important markers in genetic and breeding research. We are continuing our efforts to identify new isozyme loci and their location on rice chromosomes.
Malate dehydrogenase, MDH (E.C.18.104.22.168), and phosphogluconate dehydrogenase, PGD (E.C.22.214.171.124) commonly occur in various plant and animal tissues. PGD is involved in the formation of D-ribulose-5-phosphate via oxidative pentose phosphate pathway. MDH catalyzes reaction in the mitochondrial tricarboxylic acid cycle and also plays an important role in malate shuttle along cell compartments (Ting et al. 1975).
Three malate dehydrogenase isozyme banding patterns were found in O. sativa (Mdh-1, Mdh-2(t) and Mdh-3). However, none of these forms showed allozymic variability in 30 representative isozyme tester stocks of rice. We therefore surveyed wild species for allozymic variation using starch gel electrophoretic procedures. Polymorphism was detected between rice and wild species for three loci (Mdh-1, Mdh-2(t), Mdh-3) (Table 1). Three mobility patterns for Mdh-1 and two each for Mdh-2 and Mdh-3 were identified among cultivated and wild species (Fig. 1).
Mdh-3 pattern was studied in 11 monosomic alien addition lines (MAALS) each of O. officinalis and O. latifolia (Table 2). The allozyme pattern of the wild species for Mdh-3 was detected only in MAAL-5 (Fig. 2), indicating the possible location of Mdh-3 on chromosome 5 of the two wild species. Crosses of Mdh-3 disomic homozygotes with primary trisomic 5 have been made to further confirm the chromosome location.
Similarly, analysis of MAALs of O. officinalis, O. latifolia and O. brachyantha for Pgd-2 showed allozyme of wild species only in MAAL-6 (Fig. 3). The results show that Pgd-2 is located on chromosome 6. Ishikawa and Morishima (1989) also located Pgd-2 on chromosome 6 through linkage with Est-2.
Table 1. Polymorphism for malate dehydrogenase in cultivated and wild rices ============================================================================== Isozyme locus Allele Marker accession ============================================================================== Mdh-1 fast IR31917, IR56 O. latifolia (100914) O. officinalis (100896) O. australiensis (100882) intermediate O. brachyantha (101232) slow O. minuta (101141) Mdh-2(t) fast IR31917, IR56 O. australiensis (100882) O. latifolia (100914) O. officinalis (100896) slow O. brachyantha (101232) Mdh-3 fast IR31917, IR56 O. brachyantha (101232) slow O. minuta (101141) O. officinalis (100896) O. latifolia (100914) O. australiensis (100882) ===============================================================================
Fig. 1. Zymogram showing malate dehydrogenase polymorphism in cultivated and wild species of rice.
Table 2. Chromosomal location of Mdh-3 using MAALs of two species =============================================================================== MAAL O. officinalis (100896) O. latifolia (100914) =============================================================================== 1 NA - 2 - - 3 - NA 4 - - 5 + + 6 - - 7 - - 8 - - 9 - - 10 - - 11 - - 12 - - =============================================================================== + critical,- non critical, NA not available.
Table 3. Chromosomal location of Pgd-2 using MAALs of three wild species ============================================================================== MAAL O. officinalis (100896) O. latifolia (100914) O. brachyantha (101232) ============================================================================== 1 NA - NA 2 - - NA 3 - NA NA 4 - - - 5 - - - 6 + + + 7 - - - 8 - - NA 9 - - - 10 - - - 11 - - - 12 - - - ============================================================================== + critical, - non-critical, NA not available.
Fig. 2 . MAAL-5 of O. officinalis showing critical banding pattern for Mdh-3.
Fig. 3. MAAL-6 of O. officinalis showing critical banding pattern for Pdg-2.
Ishikawa, R. and H. Morishima, 1989. Linkage analysis for four isozyme loci, Adh-1, Acp-1, Pox-2 and Pgd-2. RGN 6: 109-112.
Ting, I. P., I. Fuehr, R. Curry and C. Zschoche, 1975. Malate dehydrogenase isoenzymes in plants: preparation, properties and biological significance. pp. 369-389. In: Isozymes, Vol. II, ed. C. L. Market. Academic Press, New York.