Regenerated plants and their sexual progeny were obtained from immature embryo-derived callus cultures of A188 inbred, and the isoperoxidase spectra were studied in their etiolated and green leaves as described elsewhere (Khavkin and Zabrodina, Russ. J. Plant Physiol., 41:754, 1994). In somaclones, in contrast to the initial plants, the leaves manifested a peroxidase band coinciding, by its mobility, with the root-specific isozyme Px12. This band was barely discernible in the young leaves of the regenerated plantlets grown in agar and became heavily stained in the green leaves of the 11 to 20-day-old plants grown in sand or soil (Fig. 1A and B).

The anodal isoperoxidase spectra in the calli obtained from different tissues were quite similar and differed considerably from the isozyme patterns of the respective explant tissues: a new band appeared in the position of the Px12 isozyme, and Px9 band staining was enhanced. The primary calli from the scutellum and the apical meristem were two exceptions from this pattern: we did not observe the Px12 band in these calli, however, the corresponding band finally appeared in the scutellum callus after several subcultures. In the roots regenerated from the calli of different origin, Px9 and Px12 staining increased to the level of the primary roots of the initial A188 seedlings (Fig. 1C).

We presume that cell dedifferentiation in vitro may somehow disrupt the tissue-specific control over peroxidase expression, and the newly established pattern of peroxidase manifestation is further maintained as a meiotically heritable state. The age-dependent quantitative changes in Px12 staining suggest that both in the calli and intact plants, this isoperoxidase could be related to vascular differentiation.

Figure 1. The fast-moving anodal isoperoxidases in intact and cultivated maize tissues. Seedling tissues (the numbers in brackets stand for the seedling age, days) : 1, endosperm (3); 2, scutellum (3); 3, embryo axis (3); 4, primary root (7), 5, mesocotyl (7); 6, coleoptile (7); 7, etiolated leaf (7); 8-10, green leaf (11, 14 and 20). Cultivated in vitro tissues: 11, primary scutellum-derived callus; 12, scutellum-derived callus after prolonged subculturing; 13, roots regenerated from scutellum-derived callus; 14, apical meristem-derived callus; 15; roots regenerated from meristem-derived callus; 16, leaf-derived callus; 17, roots regenerated from leaf-derived callus; 18, developing tassel; 19, tassel-derived callus; 20, roots regenerated from tassel-derived callus.

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