Nucleus and cytoplasm in the segregation and effects of iojap

White seedlings in the progeny of crosses of ij ij ear parents by + + pollen were demonstrated by M. M. Rhoades (Cold Spring Harbor Symp. Quant. Biol. 11:202, 1946) to be the result of changes in maternally inherited (plastid) properties, occurring somatically during ear development. L. B. Mazoti (see MNL 50:58, 1976) has demonstrated that not all + + pollen parents yield white seedlings in such crosses, and that progeny tests of plants from crosses of ij ij x + + (white-negative) strains do not reveal hidden (i.e., suppressed) white lineages. In addition, Mazoti has observed that Euchlaena cytoplasm confers much-reduced expression of ij. Possible nuclear and cytoplasmic influences on white seedlings and on iojap segregation ratios have been examined in a range of strains and cytoplasms.

Are white-negative strains common? Six inbred strains were tested by crossing onto ij ij ear parents and sampling to test for green vs. white seedlings:

Table.

Of the six strains, only Oh51A was consistently white-positive.

Do different cytoplasmic origins affect ij segregation differentially? Highly converged strains of two different inbred lines, K55 and Tr, each with six different cytoplasms, were crossed by ij ij, and the F1's were carried to F2 by crossing to the F1 involving the inbred itself, or to the F1 involving the other inbred (Table 1). While there was an overall deviation from 25% that is highly significant (22.18%), it is apparently consistent through all the families (heterogeneity is not high in the sub-families), and there is no consistent nucleus- or cytoplasm-specific deviation.

Table 1.

Does prior exposure of the cytoplasm to ij ij desensitize it to the effects of ij ij in subsequent segregations? Inbred lines were crossed by ij ij males and onto sibling +/ij and ij ij ear parents in a family segregating 1:1 (from +/ij x ij ij), and the F1's were selfed (Table 2). There was no consistent pattern of effect of ij exposure on the segregation ratios.

Table 2.

Except for the finding that five of the six inbred strains tested are whitenegative, these experiments identify no nuclear or cytoplasmic alteration of iojap segregations.

E. H. Coe, Jr.


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