著者

岩田 伸夫

出版者

九州大学

雑誌

九州大學農學部學藝雜誌 (ISSN:03686264)

巻号頁・発行日

vol.25, no.1, pp.1-53, 1970-07

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In our laboratory we have about a hundred progeny lines of rice plants descended from the plants which were exposed to atomic radiation in Nagasaki. These lines have been classified into some categories, genic mutation lines, chromosome structural changed lines and so on, according to their genetic behavior or the characteristics of their abnormal derivatives. However, many kind of variant types have occurred irregularly in the process of pedigree culture of them even now. The author planned to clarify such complicated genetic behavior of the progenies of atomic bombed rice plants. The present paper deals mainly with the results of the cytogenetical studies, First of all, the data for kind of variants, their morphological and genetical characteristics and others in the progeny lines which demonstrated before 1958 by Dr. T. Nagamatsu were arranged. As a result of this arrangement of data, it was shown that the progeny lines including chromosome structural changes ceuld be classified into three groups as follows. 1) Semi-sterile lines, which descended from the semi-sterile mother plant and segregated into normal and semi-sterile plants in the ratio of 1:1. 2) High sterile lines, which descended from the high sterile mother plant and segregated into normal, semi-sterile and high sterile plants in ratio of about 1:2:1. These sterility and the segregation ratio are caused by the reciprocal translocation. 3) Primary and/or tertiary trisomic lines derived from their sterile lines. And moreover, it was supposed that there were not a few chromosome structural changes, which is latent in these lines as homozygous conditions and can be detected only by test crossing to chromosomal standard plant. By the test crossing between chromosome standard plant and fertile plants descended from progenies of atomic bombed rice plants, the plants having chromosome structural changes were detected in 60 out of 79 lines used. According to the observation of seed fertility (s), pollen fertility (p) and the chromosome behavior at meiosis in the PMCs of the F_1 hybrids, these chromosomal changes were categorized into A (s≑p≑50%, a quadrivalent was observed), B (s≑p≑50%, a quadrivalent was not observed), C (s≑p≑50%, chromosome observation was not yet made), D (s<p, a quadrivalent was observed infrequently), E (s>p, a quadrivalent was not observed) and compound types of them. It was indicated that each of the types, A, B, C and D, was the homozygote for one reciprocal translocation and that the compound types such as double A (s≑p were lower than 25%, two quadrivalents were observed) and A+D (s<p=30%, a quadrivalent was observed but two quadrivalents were observed infrequently) were the homozygotes for two reciprocal translocations. Therefore, the semi-sterile plants which segregated in semi-sterile lines and in high sterile lines were heterozygous plants for A, B, C and D types and the high sterile plants which segregated in high sterile lines were heterozygous for the compound types of chromosome structural changes. These facts were also confirmed from their segregation patterns of fertility in the F_2 generations. Moreover, it was observed in several cases that the H hybrids between standard plant and fertile plants descended from semi-sterile lines showed the high sterile plants of compound types in addition to semi-sterile plants. It demonstrated the being of latent structural changes in sterile lines. For the identification of the reciprocal translocations isolated from progenies lines, the F_1 hybrids were compared with each other in some characteristics, with special reference to the chromosome configuration and frequency of quadrivalent at meiosis. And these translocation lines were also tested as to homology of translocated chromosomes by reciprocal crosses among them. As a result, it was confirmed in some cases that the homologous changes existed among the lines even which derived from different original lines. For example, 6 kinds of homologous changes were observed in category A, and moreover, in category D, one homologous change was identified among 10 lines which derived from the 5 original lines. Nevertheless, about 20 different reciprocal translocations were isolated. Then, they were analyzed for translocated chromosomes by means of reciprocal translocation analysis. Occasionally, the high sterile plants, which may be the heterozygote for two of chromosome structural changes, have occurred in sterile lines in the process of the maintenances and the renewals of progeny lines of atomic bombed rice plants. The cause of that was infered from the mode of occurrence, genetic behavior of them and moreover the outcrossing ratio of semi-sterile plants as follows: as a result of outcrossing, 1) the chromosome structural changes which had been latent as homozygous condition in semi-sterile lines were appeared as heterozygous condition in high sterile plants, or 2) some chromosome structural changes were introduced from other semi-sterile lines. Most of the progeny lines of atomic bombed rice plants have been maintained up to date through such high sterile generations, once or more, in process of line renewals. This fact was probably supposed the cause of the existance of the homozygous chromosome structural changes among the lines which derived from different original lines and, chromosome structural changes among the lines which derived from different original lines and, consequently, there were fewer changes than that expected in progeny lines of atomic bombed rice plants at the beginning of this study The D types, in which a quadrivalent was not observed practically, had rather higher pollen fertility (60-70%) than seed fertility, so it was suggested that the male gametes with a duplicate-deficient of translocated chromosomes may be viable in a certain case. On the E types, which had been categorized by lower pollen fertility than seed one, a bridge or a lagging chromosome was observed at the first anaphase in the PMCs and thus it suggested the presence of an inversion. Trisomic lines which have descended from the progenies of atomic bombed rice plants were not treated directly. However, some trisomics derived from reciprocal translocation heterozygotes, in which translocated chromosome had already identified, were examined for several generations as to the chromosome constitution, chromosome behavior at meiosis in the PMCs, the segregation mode of trisomic phenotypes in their progenies and so on. As a result, a general tendency was observed as follows: in early generations the chromosome constitution of trisomics which derived from translocation heterozygous plants were homo type II (primary trisomic interchange homozygote and tertiary trisomic) or hetero type (primary trisomic interchange heterozygote and tertiary trisomic interchange heterozygote) and the segregation of semi-sterile plants were observed in the hetero types; and with the generations, these chromosome constitution of trisomics became to the homo type I (primary trisomic and tertiary trisomic interchange homozygote) and finally fixed in this type which does not segregate the semi-sterile plants. In this process, the segregations of various morphological characteristics in primary or tertiary trisomics were observed according to the kind of extra chromosomes and their size of reciprocal translocations involved. Then, the endeavors to analyze the relation between the extra chromosome and the morphologica1 characteristics were made and the morphological characteristics of 11 sorts of primary trisomics were demonstrated. On the basis of those knowledge described above, the complicated occurrence of variant types and their genetic behavior in the process of pedigree culture of these progenies of atomic bombed rice plants more than 10 years period were discussed.長崎の原爆イネ後代に含まれる染色体構造変異の概要を明らかにし,その知見に基づいて過去10余年にわたる原爆イネの系統保存の過程での複雑な変異型の出現傾向とその遺伝組成について明確な説明を与えた. 1. まず,1958年までにすでに明らかにされた変異型の種類,特性,出現状態および遺伝様式などに関する資料を整理し,染色体構造変異に起因するものには大別して,相互転座ヘテロによる半稔系統群,高不稔系統群と,それらの系統から派生する一次あるいは三次三染色体植物群の存在することを明らかにし,さらにホモ状態で系統内に潜在して,検定交配によらねば検出不可能な構造変異の存在も少なくないことを推測した. 2. 染色体標準系との検定交配により,供試した原爆イネ79系統中60系統について染色体構造変異個体を検出,分離した.それらを,検定交配F_1の種子稔性(S),花粉稔性(P),花粉母細胞の減数分裂期の染色体行動によつてA型(S≑P,40~50%,4価観察),B型(S≑P,約50%,4価なし),C型(S≑P,約50%,4価不明),D型(S<P,ごくまれに4価観察),E型(S>P,4価なし)およびその複合型に分けた.A,B,C,D型はいずれも1つの相互転座の存在を,重複A型,A+D型は2つの相互転座の存在を示し;さらに半稔系統群,高不稔系統群において分離する半稔個体はこれらA,B,C,D型の転座ヘテロ個体であり;高不稔系統群に分離する高不稔個体は複合型のヘテロ個体である.この事実は,検定交配F_1の特徴とそのF_2の分離様式からも確かめられた.半稔系統群では検定交配F_1で半稔個体とともに複合型の高不稔個体が現われる場合が2,3みられたが,これは潜在変異の存在を示すものと思われる. 3. 各系統に包含される相互転座の特性を検定交配F_1の特徴,とくに4価染色体の形状,出現頻度などについて比較検討するとともに,転座系統間の相互交配によつて相同性を検定した.その結果,原系統の異なる系統間にも相同な変異の存在する場合が少なくなかつた.A型で6例,D型では5原系統に由来する10系統に相同な変異が存在した.それでも,約20の異なる相互転座が検出されたので,これらはさらに転座分析により転座染色体を同定した. 4. 4価染色体のほとんど観察されないD型は,種子稔性にくらべ花粉稔性がかなり高い(63~74%)ことから,転座染色体の重複,欠失を伴なつた配偶子の生存の可能性が考えられる. 5. 種子稔性は正常で花粉稔性のみ半稔性を示すE型は,第1後期に染色体橋や遅滞染色体が観察され,逆位の存在することが考えられる. 6. 原爆イネ系統の保存,更新の過程で偶発的に出現する高不稔個体は,複合型変異のヘテロ個体であり,出現傾向,遺伝行動さらには半稔個体の他殖率などから,その成因は,他系統との交雑により, 1) ホモ状態で潜在していた変異がヘテロとして発現したか, 2) 他の系統の変異が導入されたかのいずれかであると推定した.原爆イネ後代系統の多くが系統更新の過程でこのような高不稔世代をへて今日にいたつていることが,異なる原系統に由来する系統間に相同な変異が存在し,原爆イネ系統に含まれる染色体構造変異を予想以上に少なくしている原因であろう. 7. 原爆イネ後代に出現した三染色体系統を直接取扱うことはしなかつたが,転座染色体の明らかな数系統から派生した三染色体植物を数世代にわたつて染色体構成,染色体行動,表現型の分離様式などについて追跡した結果,転座系統から派生した当初はその染色体構成はホモII型か,あるいは半稔個体を分離するヘテロ型であり,いずれも世代が進むにしたがつて不稔個体を分離しないホモI型に固定する傾向がみられた.その過程で,一次あるいは三次三染色体植物の表現型の分離が観察されるが,転座染色体の種類,転座の程度によつて4つの表現型が明瞭に区別されるものからそうでないものまで存在することを認めた. 8. 転座染色体の明らかな転座系統の後代から派生した三染色体植物について,過剰染色体と三染色体植物の形態的特徴との関係を解析し,さらに11種の染色体を含む一次三染色体植物の形態的特性を明らかにした.