Study of intralocus events leading toRstippled (Rst) recombinants inZea mays
✍ Scribed by G. Gavazzi; D. Calati
- Book ID
- 104626361
- Publisher
- Springer Netherlands
- Year
- 1972
- Tongue
- English
- Weight
- 682 KB
- Volume
- 43
- Category
- Article
- ISSN
- 0016-6707
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✦ Synopsis
The two main components of the R locus, designated P and S condition the production of a red pigment, chemically identifiable with cyanidin 3glucoside, in the plant and seed tissues respectively. In this paper we present some data on the structural organization in terms of its P and S components of an unstable form of R, designated R St, and of two of its derivatives.
The superscript st (stippled) refers to a distinctive pattern of aleurone variegation conditioned by R st. The instability is seemingly the result of the interaction oI the S component of Rat with an adjacent element affecting its gene action.
The two stippled derivatives analyzed are RSk (smoky) that conditions a different pattern of aleurone variegation and Ree (self-colored) characterized by a homogeneous aleurone pigmentation. Assuming that R st is a gene complex, p S Bt in structure, heterozygous P s / p S st individuals should yield P S st and p s recombinants, besides the parental P s and p S Bt strands.
Accordingly P s / p S st male parents, carrying appropriate outside markers, were crossed with a p s / p s line. Among the progeny of this cross the exceptional individuals carrying nonparental strands were isolated as presumed intralocus recombinants and their flanking markers constitution was established. This analysis, extended to the p S 8k and p S sc complex shows :
(1) a disparity in the production of the two nonparental strands, with an excess of p s over P S st (2) the occurrence of a distinctive morphology in about one half of the exceptional individuals carrying a p s strand (3) negative interference in conjunction with intralocus events, on the hypothesis that the latter are the result of reciprocal exchange between genes of the R complex. The possible origin of the nonparental strands through a mechanism of gene conversion or chromosomal deletion is considered and the evidence in favour or against either hypothesis is discussed.
The occurrence of P S st strands offers the opportunity to analyze the effect of S st on P gene action. This test was performed by comparing the pigment concentration and *) Research partially financed by the C.N.R. (Consiglio lqazionale delle Ricerehe, Rome).
G. GAVAZZI AND D. CALATI distribution of individuals genotypically P Sut/p s and p S Bt / P s. The comparison shows that seedlings of the two genotypes differ significantly both in the amount of pigment produced and its distribution. While the former determines a weak pigmentation, phenotypically recognizable as sectors or fine stripes along the primary root, the latter shows a homogeneous pigmentation amounting to six times that found in P S 8t seedlings.
These observations seem to indicate that both P and S, when lying in coupling on the same chromosome together with the instability factor, are coordinated in their action by the latter.