Higher Polyploids Research Articles

CYTOGENETICS OF RUBUS. III. MEIOTIC INSTABILITY IN SOME HIGHER POLYPLOIDS

Thompson, Maxine M. (U. California, Davis.) Cytogenetics of Rubus. III. Meiotic instability in some higher polyploids. Amer. Jour. Bot. 49(6): 575–582. Illus. 1962.—Meiotic instability occurred in low frequency in polyploid Rubus varieties, ‘Young,’ ‘Boysen,’ and ‘Mayes.’ Subdivision of the chromosome complement into 2 or more groups that function independently within the cell, nondisjunction of chromosomes, and unequal distribution of the chromosomes to the polar regions at anaphase were noted at either or both meiotic divisions in the pollen mother cells. The term complement fractionation is suggested for the phenomenon of independently operating groups of chromosomes of variable numbers within meiotic as well as mitotic cells. The presence of PMC's with unusual chromosome numbers indicates a pre‐meiotic instability similar to that observed in meiotic cells. With such a cytological mechanism a polyploid organism can produce gametes with extremely variable chromosome numbers. Some of these gametes will be functional due to a tendency for the formation of balanced genomes. The significance of complement fractionation is considered in relation to unusual breeding results, its value as a tool for plant breeders and its role as an evolutionary mechanism. Polyploids are considered as a storehouse of variability which occasionally, by means of the cytological mechanism described, can be released in the form of distinct, new segregants at different levels of ploidy.

Cytogenetics of Rubus. III. Meiotic Instability in Some Higher Polyploids

Cytogenetics of Rubus. III. Meiotic Instability in Some Higher Polyploids

Cytotaxonomy of Australian Danthonia

Cytological and cytogenetic studies of 29 Australian species of Danthonia revealed an extensive polyploid series ranging from 2n = 24 to 2n = 120. Meiosis was regular and fertility high in the species. Field hybrids were detected by aberrant chromosome number, meiotic behaviour, and reduced fertility. An extensive series of interspecific crosses resulted in some viable hybrids but many combinations failed or gave F1 plants which failed to flower. Most viable F1 plants were highly sterile. Diploid hybrids were completely sterile, but in higher polyploids crossing was more often successful and hybrids had increased fertility. Meiotic pairing and chiasma frequency were drastically reduced in all F1s. Multivalent associations indicated gross structural rearrangements. The restoration of fertility by chromosome doubling indicated cryptic structural changes. Neither cross compatibility nor meiotic behaviour showed any strong relationship with taxonomic grouping. These results together with the intermediate morphology of F1s and the increased morphological variation in polyploid forms of D. caespitosa and D. linkii strongly suggest alloploidy as the main mechanism of evolution of the polyploid species. Twenty-three of the species had Panicoid type of epidermis and Festucoid chloroplast arrangement. The exceptions were D. pallida, D. procera, D. frigicla, D. nivicola, D. nudiflora, and D. sp. indescr. These studies throw light on the relationship of the arid form, D. bipartita, the alpine forms D. frigida, D. nivicola, and D. nuclifiora, and the highly variable forms such as D. caespitosa and D. linkii with the rest of the genus. Plant improvement by conventional methods would be virtually impossible unless restricted to high polyploids and intraspecific crossing, but true-breeding, highly fertile amphidiploids could be produced.

The Chromosomes of Six Melaniid Snails (Gastropoda: Prosobranchia)

1. The chromosomes of six Melaniid snails have been studied. The chromosome numbers of the various forms are as follows.Melania crenulata _??_ 2n=34+X=35Paludomus tanschaurica _??_ 2n=36+XY=38Melanoides tuberculatus (diploid race) _??_ 2n=32Melanoides tuberculatus (polyploid race) _??_ and_??_ 90-94Melanoides lineatus _??_ and _??_ 71-73Melanoides scabra _??_ 76-782. The chromosomes of all the Melaniids studied are metacentric and in this respect their chromosome complements are similar.3. All the Melanoides except the diploid race of M. tuberculatus are high polyploids and these add to the only one instance of polyploidy so far known in Molluscs.4. The co-existence of parthenogenesis and polyploidy may account for the numerous forms of Melanoides, their variability, wide distribution and consequent taxonomic difficulty. In view of the prevailing confusion in identification and nomenclature of the Melaniids in general, a cytotaxonomical approach seems imperative. An indication of this is provided by the two races of M. tuberculatus.5. The two cytologically distinct races of M. tuberculatus though not markedly different with respect to size and external morphology do show ecological physiological and biochemical differences. Polyploidy seems to confer hardiness and selective advantage.

A chromosome survey of indian dioscoreas

The present paper deals with the chromosome numbers of nine species of wild and cultivated Yams. Five species, namely,D. pubera, D. deltoidea, D. hispida, D. belophylla andD. esculenta, have been worked out for the first time. InD. alata andD. bulbifera different chromosome races for the Indian forms have been recorded besides the ones reported by previous workers. It is interesting to observe that the Japanese races ofD. oppositifolia andD. pentaphylla are higher polyploids than the Indian forms reported here.

Polyploidy and vitamin C inEmblica officinalis gaertn

Emblica officinalis collected from various parts of India was found to have chromosome number 2n=98=14x and is therefore a much higher polyploid than the one reported on by Perry which is a tetraploid 2n=28. Cultivated forms ofEmblica officinalis have variable numbers ranging from 2n=98 to 2n=104 and these have larger fruits. A comparative analysis of Vitamin C content of wild and cultivated varieties is given. Ascorbic acid content is found to be directly proportional to the size of the fruit and fruit size is correlated with the presence of a few extra chromosomes in the already high polyploid.

HYBRIDIZATION STUDIES ON FOUR HEXAPLOID SOLANUM SPECIES IN SERIES DEMISSA BUK

The presence of a polyploid series of species in the tuber-bearing Solanums was first demonstrated by Smith (1927) and confirmed by Rybin (1930). The basic chromosome number was considered to be 12, and in addition to numerous diploid, triploid, tetraploid and pentaploid species these authors found one hexaploid, Solanum demissum Lindl. (2n=72). In point of fact the haploid number of 36 had already been noted by Salaman (I926), though the full significance of S. demissum as a higher polyploid was not at that time realized. Until quite recently S. demissum, which is a wild blight resistant species from the high mountains of Mexico, was the only hexaploid known in this group. In the last two or three years, however, four other hexaploid species have been discovered, namely S. brachycarpum Corr., S. guerreroense Corr., S. spectabile (Corr.) Hawkes and S. moscopanum Hawkes. The first three of these are, moreover, quite closely related to S. demissum in their morphological features. Yet, as we shall attempt to show in the present communication, they behave as good species, forming infertile hybrids with each other and with S. demissum. The taxonomic grouping, together with the geographical distribution and a reference to the first published chromosome counts, is given in Table i.

Study on the high polyploid chromosomes and their endoreduplication of Watanabe ascites hepatoma

Study on the high polyploid chromosomes and their endoreduplication of Watanabe ascites hepatoma

Structure and functional capacity of the ovaries of higher polyploids (4N, 5N) in the Mexican axolotl (Siredon or Ambystoma mexicanum)

Structure and functional capacity of the ovaries of higher polyploids (4N, 5N) in the Mexican axolotl (Siredon or Ambystoma mexicanum)

Nucleoli Numbers in <i>Danthonia</i> Polypliods

It has been indicated that the species in the genus Danthonia constitute a polyploid series. Species which are 2n, 4n, 6n, 8n, and 12n have been demonstrated. Nucleoli numbers were counted in these species at mitotic telophase. It was observed that the diploids produce either 2 or 4 nucleoli, the tetraploids 2 or 4, the hexaploids 2 (except for the 42-chromosome hexaploid with four nucleoli) and all the higher polyploids four nucleoli.The fact that D. disticha possesses both a chromosome pair having secondary constrictions and a satellited pair, whereas D. curva (both diploids) lack a satellited chromosome pair was assumed to indicate that the first mentioned species retained the original diploid condition. D. curva evidently therefore got rid of one nucleolus-organizer pair. Tetraploids with four nucleoli could have originated out of diploids with two nucleoli. Similarly the octaploids could have been derived from tetraploids with two nucleoli, and the 72-chromosome species out of hexaploids with only a single nucleolus pair.It was assumed that the extra nucleolus-organizers could have got lost through mutations. The fact that the genus is very old seems to support this assumption. Taking all the polyploids into consideration it would appear as if they tend to revert back to the diploid condition as far as nucleoli are concerned.

EFFECT OF ENVIRONMENT UPON CHROMOSOMAL PAIRING OF SOME SPECIES AND HYBRIDS OF POA

WHILE THE PAIRING of chromosomes reflects the affinities of the genes contained within them, the expression of this phenomenon, like every other genetical character, is subject to both genetic and environmental influences. In order to measure the degree of pairing within a given or hybrid, it is necessary that the effects of the more common environmental variations be evaluated. This is especially important for many of the genus Poa in which high polyploid-y and inter-specific hybridizations, coupled with apomixis, have resulted in the formation of species which normally show irregularit'es in chromosomal pairing. Pairing studies in this genus are not concerned with distinguishing normal as opposed to irregular pairing, but with comparing plants all of which show irregularities, though in differing degrees. Moreover, even within the same anther there is variability of chromosome pairing from cell to cell, and consequently the observations must be made on a statistical basis. In the present investigation the effects of several environmental influences were studied as a necessary first step in a program of investigation requiring the interpretation of chromosome pairing in many and hybrids of Poa. MATERIALS AND METHODS.-The plants used were individuals of two of Poa and a few interspecific hybrids. They are part of a study of the evolution and breeding potentialities of the bluegrasses begun in 1943 by Clausen, Keck, and Hiesey in cooperation with the United States Soil Conservation Service. All the forms used were high polyploids ranging from hexaploids with 2n 42 to 14-ploids having approximately 2n 98 chromosomes. The included Poa ampla Merr., P. nevadensis Vasey, and several different combinations of the hybrids P. ampla X pratensis, and P. ampla X compressa. These hybrids, being results of intersectional crosses, represent combinations of widely divergent genomes.

Cytology and Breeding Behavior of Twin Plants of Bromus inermis

1. Twenty-eight sets of twin plants of Bromus inermis were successfully grown to maturity. Much of the original variation in vigor evident as seedlings had disappeared before the plants were established in the field, suggesting that the seedling differences in vigor were perhaps largely due to the relative positions of the embryos to the endosperm. All sets of twins differed in at least minor characters as adult plants. 2. Large differences occurred in seed-set following both self- and open-pollination. This was evident both between and within twin sets. The percentages of pollen stainable with IKI varied from 0 to 99.4, the differences being approximately as large within as between sets. Pollen of a given plant generally varied somewhat in size. Three major classes were found in the population examined, these having diameters approximating 50, 61-78, and 84-88 μ. 3. Variations were noted in the frequency of irregular meiotic divisions between and within sets. Generally there was a tendency for the amount of this irregularity to be inversely related to the extent of seed-set following both self- and cross-pollination. 4. The plants of the I1 progeny from some plants were materially reduced in vigor when compared with those of the I0 progeny. Those from other plants were not materially reduced in vigor following inbreeding, This relationship was evident both within and between sets. The data indicate also that low self-fertility may not be closely related to the occurrence of plants of superior vigor in the I1 generation. 5. Comparisons within 28-, 56-, and 70-chromosome plants and their progenies indicate close similarity of behavior throughout gametogenesis irrespective of the degree of polyploidy. Seed-set was greater, however, in the higher polyploids, other behaviors being approximately equal. 6. It would appear evident that the twins were not monozygotic when considered with respect to the morphology and cytology of members of a given set. The behavior of the progenies following inbreeding and open-pollination was also in accord with this interpretation.

Cytological Studies of Forage Plants, I. Grasses.

The writers studied the chromosome numbers in 26 species or varieties of Gramineae which flower mainly from spring to summer in the northern part of Kanto district.1). The basic number of chromosomes is 7 with the exceptions of 4 species that have 9 or 10 in haploid.2). 30 percent of grass materials was revealed to be diploid, 50 percent tetraploid, 10 percent hexaploid and 10 percent octoploid. Thus the polyploids, especially the tetraploid are predominant in this district from spring to summer.3). It was found that, in the genus Agropyron, the high polyploid species are to be more adaptable in high elevation than the related lower polyploid ones.4). Some grasses naturalized from the cultivation showed high polyploidy.5). In the genera Agropyton, Agrostis, Bromus and Poa, the higher polyploid species are more useful for the forage plant than the lower polyploid ones.

The Origin of Multiple Macrogametophytes in Poa pratensis

The origin of multiple macrogametophytes in Poa pratensis was studied and the results presented in relation to known breeding behavior of plants from both plural and single embryos. Eggs developed following meiosis may result in haploid-diploid and diploid-diploid relationships in the plural embryos and in the mature plants. The origin of these plural embryos is (1) from two members of the egg apparatus and (2) from two macrospore mother cells. Embryo sacs developed from somatic or nucellar cells may form diploid-diploid, diploid-triploid, and diploid-tetraploid combinations of plural embryos and mature plants. The diploid-diploid combinations are considered to arise from two somatic egg cells or from an egg and a synergid of a single embryo sac that develop parthenogenetically. The diploid-triploid combination probably arises in a similar manner; the egg of one embryo sac develops parthenogenetically, whereas that of the second develops as a result of fertilization by a male gamete carrying approximately the reduced chromosome number. Triploid-triploid combinations could form by the fertilizing of two cells (two eggs or an egg and a synergid). The diploid member of diploid-tetraploid plural embryos might originate in the manner indicated previously for other combinations, the tetraploid by the parthenogenetic development of the egg with a somatic doubling of the chromosomes of the nuclear complement at the time of the zygotic division, or fertilization with an unreduced or restitution male nucleus, or with a high polyploid gamete. The chromosome complement of the male gamete would have to equal that of the egg nucleus. It is considered quite improbable that origin of tetraploids involving gametes would be of common occurrence. Plural embryos were found to arise from reduced macrospores and nucellar cells in the same ovule. The embryos resulting from these would be diploid-diploid or diploid-triploid, depending upon whether fertilization of only the egg of the reduced macrogametophyte or fertilization of all of the several members, reduced and unreduced, occurred. "Supernumerary embryo sacs" might develop from nucellar "bud" cells of the wall of the gametophytic cavity. These embryo sacs may be imperfect and nonfunctional, or they may be complete and account for some of the instances wherein proembryos or well-developed embryos are located at various positions other than at or near the micropylar portion of the seed. The observations are incomplete for such a manner of origin of plural embryos. Macrosporogenesis in the haploid plant was quite similar to that reported for the higher polyploids of the species. The sterility of this plant is undoubtedly due to genetic rather than to evident cytologic disturbances.

A KARYOSYSTEMATIC STUDY OF THE GENUS AGAVE

A KARYOSYSTEMATIC STUDY OF THE GENUS AGAVE