作成者 |
作成者名
所属機関
所属機関名
Department of Agriculture, Kyusyu Imperial University
九州帝國大學農學部園芸學 |
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本文言語 |
英語
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出版者 |
Kyushu Imperial University
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九州帝國大學農學部
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発行日 |
1945-05
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収録物名 | |
巻 |
7
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号 |
9
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開始ページ |
281
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終了ページ |
396
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出版タイプ |
Version of Record
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アクセス権 |
open access
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Crossref DOI |
https://doi.org/10.5109/22602
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関連DOI |
http://www.agr.kyushu-u.ac.jp/
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関連URI |
http://www.agr.kyushu-u.ac.jp/
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関連情報 |
http://www.agr.kyushu-u.ac.jp/
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PISSN |
0023-6152
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NCID |
AA00247166
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レコードID |
22602
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査読有無 |
査読無
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主題 |
Brassica
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Raphanus
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F₁ Hybrids
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Megasporogenesis
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Brassica
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Raphanus
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F₁ Hybrids
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Megasporogenesis
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注記 |
(1) During the period of 1926-1937, the author tried a large number of genus-crosses between Japanese radishes (Raphanus sativus) and various cultivated Brassica species, and succeeded in obtaining true F_1 hybrids in the following 11 different crosses, the number of F_1 individuals raised amounting to 22 in all (Cf. Table 2). All the F_1 hybrids covering (1)-(8) had the same genome constitution "Rc" and so they were treated in Part I, while the remaining three F_1 hybrids, (9)-(11) with "Rab" or "Rbc" genomes, were treated in Part II. (2) Remarkable differences prevailed in degree of success in obtaining those intergeneric F_1 hybrids, depending, on one hand, directly on the species, strains, or individuals concerned, and, on the other, on various environmental conditions surrounding the mother plants. Crosses between B. oleracea and R. sativus were much more successful when the latter species was taken as the seed parent. Only one reciprocal hybrid B. oleracea x R. sativus (F, K) was obtained by the author, and he could not notice any differences in characters between those reciprocals. As usually the case with the interspecific crosses, F₁ hybrids between Raphanus and amphidiploid Brassicas, namely, B. carinata, B. cernua, or B. juncea, were only obtainable when the latter species of larger chromosomal number were taken on the maternal side. (3) Morphological characters of those F_1 hybrids differed to some extents even in the same species combination, in both di- and tri-genome hybrids, according to the genotypic constitution of the respective plants. From very early stage of growth on, there were noticed marked heterozygous nature existing in the hybrid organisms raised from the same cross. The development of F_1 embryos, and the size and the germinating power of F_1 seeds differed remarkably. Weak seedlings induding albinos and other chlorotic ones, which soon died out, were produced to a certain extents together with normal vigorous sister individuals. (4) Di-genome "Rc "-hybrids showed a strong tendency of heterosis, in the height of plant, in the number of side flowering branches, and in the. number and size of leaves. Every morphological character of those F_2 plants was. in some measure intermediate, though a certain parental characters predominated in the F_1 plants. (5) Tri-genome F_1 plants, "Rbc", also showed as vigorous a growth as the "Rc "'plants, while F_1 B and F_1 C plants of "Rab" did not. The morphological characters of the Brassica parent, which has an amphidiploidal number of chromosomes, usually predominated in F_1 hybrids, the situation being quite similar to that generally recognized in the interspecific hybrids. (6) Marked prolongation of the blooming duration and the enlargement of flowering clusters occurred in "Rc" and "Rbc" –F_plants. These characters were, no doubt, partly caused physilologically in connection with the nearly complete sterility of those F_1 hybrids. Some F_1 individuals of R. sativus x B. oleracea showed a strong regenerative activity, outliving two 01: three seasons or more. (7) The intergeneric F_1 hybrids were extremely sterile. But there could be stilI noticed some differences in the degree of fertility among them. Some "Rc"-F_1 plants were completely sterile, and the most fertile one produced several viable F₁ seeds Furthermore, one of the two sister F_1 individuals raised from a certain cross R. sativus x B; oieracea, F_1 D, was completely sterile, while the other was partiaily fertile, though there could be noticed no definite difference in their chromosome behaviours in meiosis. F_1's H, D, and G plants obtained from a similar cross R. sativus x B. oleracea, F, E plants from R. sativus x B. alboglabra, and F_1 F plants from B. carinata x R. sativus, produced several F₂ seeds respectively, and the author succeeded in raising F₂ progenies from these crosses. Fertility problems were also discussed in connection with the karyological behaviours of those F₁ hybrids. (8) Karyological studies were carried out with all the F_1 individuals, 22 in number, above mentioned. Chromosome numbers were reascertained for all varieties and strains used in hybridization, revealing no irregularities at all. (9) All the F_1 hybrids between R. sativus and B. oieracea, including F_1 R. sativus x B. alboglabra, had exclusively 18 chromosomes in diploid state. Somatic number of chromosomes of trigenome F_1 hybrids, B. carinata x ,R. sativus (F₁ F), B. cernua x R. sativus (F₁ B) and B. juncea x R. sativus (F_1 C), also showed exactly the sum of the haploid parental numbers, namely, 26, 27, and 27. (10) Studies of the F_1 microsporogenesis were mainly confined to the stages after diakinesis. Special attention was payed on the association of chromosomes in the heterotypic division. F_1 hybrids, R. sativlfs x B. oieracea, B. oleracea x R. sativus, and R. sativus x B. alboglabra, all of which having the same "Rc" genome constitution, showed variable chromosome pairing according to the parental varieties or strains used (Cf.Table 5 and Fig. 30). (11) Of those "Rc"- F_1 hybrids, F_1's A, D and E plants did not show any positive evidence of chromosome pairing, producing exclusively 18 univalents, while the remaining F_1's H, I, J, G and K produced variable number of bivalents, maximum variation being respectively (0-5)Ⅱ, (0-4)Ⅱ, (0-6)Ⅱ, (0-3)Ⅱ, and (0-5)Ⅱ. (12) F_1 B and F_1 C plants, each with "Rac" constitution, also produced no bivalent chromosome, while F_1 F plants with "Rbc" produced variable number of bivalents, the number of which ranged between zero and four (Cf. Tables 7 and 8). (13) The amount of chromosome pairing also varied, within certain limit, with individuals as well as flowers. Thus it was ascertained that the chromosome pairing depended not only on the genotype but also on the environmental conditions, external and internal. Nature of those paired chromosomes, whether they are of autosyndetic or of allosyndetic, was discussed and suggested. (14) Each frequ ency distribution polygon of paired chromosomes represented by Fig. 30 did not follow the type of chance distribution, but took generally a more or less distorted form. Such a distortion of distribution was accounted for by the presumption that each pair of those associated chromosomes had more or less different pairing potentiality or it had different amount of partially homologous segment or segments in common (15) Considerable differences existing in the amount of pairing potentialities in "Rc"- F_1 hybrids, namely, from complete absence of pairing to (0-6)Ⅱ pairs at maximum, are attributable mainly to certain differences existing between the varieties or strains concerned in crossings. This situation was discussed in connection with the problems of intraspecific evolution. (16) The bivalent chromqsomes appeared in the present F_1 hybrids had usually one chiasma and bivalents with two chiasmata were encountered very rarely. Terminalization of chiasmata was nearly complete at the I-Metaphase. (17) The author found, in "Rc "-hybrids, five metaphasic figures, each containing one trivalent chromosome. Two figures were found in F_1 H, one figure in F_1 I and two figures in F_1 K. No higher multivalents were encountered at all. Such trivalent chromosomes would have been caused by the spontaneous chromosome alterations such as translocation or like. (18) Usual course of meiosis in PMCs was similar with all the F_1 hybrids examined. Bivalent chromosomes took a regular position on the equator at the I-Metaphase, and they disjoined later regularly into their halves. Univalent chromosomes behaved in two ways, a part of them splitting at the I-Anaphase and the rest at the II-Anaphase. Behaviour of chromosomes in homotypic division also followed the typical way, and the diad chromosomes divided equationally at the II-Anaphase, while the monad ones were lagging behind. Some of the lagging chromosomes showed splitting, but they did not divide again. The author, however, obtained an exceptional case of II-division in F_1 B, B- cernua x R_ sativus, where all II-Meta phasic chromosomes, both diad and monad ones, appeared arranged themselves on the equatorial plane and they divided equationally. Thus some of those monad chromosomes, no doubt, had undergone division twice. (19) The majority of F_1 sporads were higher polyads rather than tetrads, containing supernumerary small spores produced by the lagged chromosomes excluded from the ordinary major nuclei. Nearly all of the F_1 microspores thus produced ceased to grow sooner or later and degenerated finally, owing perhaps to the genetic unbalance of their nuclear contents. (20) Restitution at the I-Anaphase occurred not infrequentty, and its frequency occurrence varied with the kinds of crosses and so also with the genotypic differences of the hybrid individuals, though it seemed to be more or less affected by some environmental conditions (See Table 6). The amount of diads produced by such restitution must have an intimate relation to the fertility of the hybrid individuals. (21) Following several irregularities were noticed in the F_1 meiosis, though some of those irregularities may not be attributed directly to the hybridity itself: (i) The occurrence of giant (polyploid) PMCs among the normal diploid ones was noticed not infrequently, The mode of occurrence of this irregularity was quite similar to that already reported by the author in a certain strain of B. japonica. (ii) Syndiploid PMCs were observed in some rare occasions. Such irregular PMCs were also considered to have been derived, like (i), by the irregular premeiotic cell division. (iii) Plasmodium-like cells or tissues were noticed rarely in some anther-locules of F₁ A and F₁ D plants. (iv) PMC with two or three minor spindles instead of the ordinary one was observed not infrequently in F_1 E plants, R. sativus x B. alboglabra. Total number of chromosomes appeared on such minor spindles in a PMC was always exactly 18, i.e., the diploid number of that F_1 hybrid. The origin of these abnormal spindles was attributed to the nuclear budding, which was observed rather frequently in the hybrid nucleus at meiotic prophase, but not to cytomixis. (v) Cytokinesis after the second nuclear division did not complete in some occasions, or rather frequently in F₁ E hybrid, R. sativus x B. alboglabra. In some monad spores thus resulted, fusion of micronuclei was detected to occur. A giant nucleus caused by such fusion contained nearly di-diploid number of chromosomes. (vi) In some F₁ anthers, interruption of division processes occurred at various stages in meiosis, and such PMCs soon degenerated. In some exceptional cases, PMCs degenerated at their premeiotic stages without undergoing division processes. (vii) In some rare F, anthers, monad spores were produced directly from the archesporial cells without undergoing meiosis. The author could not tell the future destiny of such abnormal spores. (22) Megasporogenesis and female gametophyte formation were studied in some details in the case of F₁ D hybrid, R. sativus x B. oleracea, though they occurred only in a slight percentage of F₁ ovules. Megasporogenesis seemed to proceed quite similarly as the microsporogenesis. After meiosis, one of the iour cells produced, the one lying at the chalazal end, usually underwent further divisions and produced an emhryo-sac in quite a usual manner. The mature embryo-sac had the typical appearance, containing in it two synergids, three antipodals, one egg-cell and two pole nuclei. The formation of such a matured embryo-sac occurred only in a very small percentage of the ovules produced. Degeneration occurred at various stages of both the megasporogenesis and the female gametophyte development. Some EMCs degenerated without undergoing meiosis. Various kinds of abnormal ovules examined were also described in some length. (23) In conclusion, the author discussed various problems pertaining to the species formation in Brassica and Raphanus, inferring the data obtained by the present investigation as well as the result of works hitherto carried out by other authors. In the genus Brassica there prevails a remarkable development of aneuploidy, as shown in Table I, therefore the studies on the genus are of very deep significance in connection with the general problem of the origin of aneuploidy. (24) Genome differentiation in minor order may be understood as a differentiation of genes. The differentiation of this category will result through an accumulation of simple gene mutations. The group of Brassica species with 10 chromosomes ("a") or 18 (" ab ") may have developed mainly through such genome aifferentiation. (25) Another category of genome differentiation occurs through chromosomal variations, which proceed in two ways, structural and numerical. Structural variations will produce a group of genomes which show various established interrelationships among them. The variable amounts of chromosome pairing noticed amongthe Fl hybrids raised between R. sativus and B. oleracea are ascribed as an expression of such genetic differentiation of the genomes concerned. Those minor intraspecific structural variations seem to the author to be so meagre in order that they cannot be detected by the ordinary varietal or racial crosses, as each pair of chromosomes relatively changed to that minor extent may possibly associate. With the progress of such differentiation, association quantity between two genomes decreases, showing a gradational series of variation, and at last there may no longer occur any paired chromosomes at all. The formation of a quite new genome will. result . in this manner. Thus the author suggested that the minor intra-specific differentiation of a certain species may also proceed in a way quite similar as in the inter-specific situation, though less in its extent, leaving no intrinsic distinctions between those two situations of genome differentiation. (26) In connection with the "secondary balance" of genomes, the hybridization, accompanying the doubling of chromosomes, has, no doubt, played a great rOle on the species formation in Brassica. As the decisive case of such "secondary balance" in nature, three amphidiploid species derived from each two of the three primary genomes, i.e., " a ", " b " and "c", are well known in the genus Brassica. Examples of artificial raising of some amphidiploid forms and of some new Raphano-Brassica amphidiploid forms are also reported by several workers. (27) There exist four different kinds of elementary genomes, namely, "a ", "b ", "c " and "R ", among Brassica and Raphanus, and these genomes are consisting of 10, 8, 9 and 9 chromosomes respectively. Cytology is considered to give a conclusive clue to explain the origin of those genomes, of which chromosome numbers are in such a marked aneuploidy relation, though there also exist various other ways of approach. As the most reliable and direct cytological mean, the author has taken up "genome analysis ", based on the actual primary pairing of chromosomes in interspecific or intergeneric hybrids. Doing thus the author discussed the interrelationships existing among the genomes above mentioned from the data obtained on the present intergeneric F₁ hybrids, referring also to the results of other workers on the similar hybrids and on various interspecific ones raised among Brassica species. The author also pointed out in that connection several factors which may affect the chromosome pairing. (28) Manner of chromosome pairing in meiosis of various intergeneric F₁ hybrids hitherto worked out between Raphanus and Bmssica and also those of various other Brassico-Raphanus hybrids as well as of various interspecific Bmssica hybrids, are summarized in Tables 11-14. (29) Genome interrelationships, which are suggested from the above chromosome analyses, are represented schematically in Diagram 1 (page 381). Though the diagram is yet neither perfect in certain points nor sufficient in minor details, it may suggest the fact that all those genomes, "a", "b", "c" and "R", are originated from a common basic genome or an "Urgenom ". (30) The author has also made a discussion on the proposals to make clear such a basic chromosome set or common basic genome of Brassica and Raphanus on the ground of "secondary association" hypothesis. But the hypothesis itself, according to the author's view, cannot be approved yet as a thoroughly proved one of experimental cytology. (31) As described above, it is clearly made known that the "secondary balance' has played a very important part in the evolution of genomes in Brassica and Raphanus. The author discussed, in that connection, on the general problems concerning the establishment of "secondary balance ", through which a series of genomes in aneuploid relation might have been produced.
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登録日 | 2012.07.14 |
更新日 | 2022.11.11 |