Alcohol dehydrogenase isozyme variants
--Jashir K. Madan, P. Gayen and K.R. Sarkar

ADH isozyme patterns were analyzed in scutellar tissues from maize seeds soaked 12-60 h, comprising 120 diploids carrying A C R markers and 42 haploids derived from the same stock. Tris-soluble samples were run in an alkaline starch gel system applying 20 mA current for 4 h.

All haploids and diploids homozygous for ADH showed either a fast moving densely stained ADH-2 band along with the fast moving faintly stained ADH-1 band or a slow moving ADH-2 with the slow moving ADH-1 band (nomenclature according to Scandalios, Biochem. Genet. 3:37-79, 1969). Heterozygous diploids, on the other hand, showed a dimeric nature for ADH-2 giving three clear bands (fast moving, intermediate and slow moving in 1:2:1 intensity), and a monomeric nature for ADH-1 giving only two bands (fast moving and slow moving in 1:1 intensity) (Fig. 1). In none of the cases, out of a total of 162 seeds analyzed, did ADH-2 and ADH-1 bands move differentially, i.e., a slow-migrating ADH-1 band always appeared with a slow-migrating ADH-2 and vice versa.

This situation is better explained following Scandalios' monomer-dimer hypothesis rather than Schwartz' dimer-dimer one (Schwartz, PNAS 56:1431, 1966). Considering the tight linkage between the two loci as observed in the present study as well as by Scandalios, these appear to be located on the same chromosome. Thus, the ADH-1 band (faintly stained) observed in the present study can not be ADH-2 of Schwartz, the locus for which is known to be on chromosome 4. Moreover, ADH-2 was reported to be dimeric in nature, in which case the heterozygote should have three bands. This is not observed in even a single case. However, a low intensity band co-migrating with ADH-2 (anodal to both S & F) was observed. This suggests the compound nature of the locus for ADH-2, but this low intensity band is not synonymous with the ADH-C of Schwartz and Endo (Genetics 53:709-715, 1966).

The pattern of bands was very consistent over a period of 12 to 60 h of soaking. No significant difference in band intensity was observed either at different periods of soaking or between haploids and diploids as measured by densitometry.

Thus, it needs to be confirmed further whether ADH-2 and ADH-1 in the present study are determined by two separate (linked) loci on chromosome 1 producing dimeric and monomeric complexes.

Figure 1. Schematic representation of ADH isozyme variants in scutellum of maize. A = diploid, heterozygous for both the loci; B, C = diploid, homozygous for slow moving and fast moving bands for both the loci.

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