Spontaneous Meiotic Chromosome Breakage in Natural Populations of Paeonia Californica

Abstract

THE AMERICAN SPECIES of Paeonia, P. calilornica and P. brownii, show in natural populations a high degree of meiotic irregularity. They have evolved a cytogenetic system of which the most prominent feature is permanent translocation heterozygosity, comparable to that of Oenothera (Stebbins and Ellerton, 1939; J. Walters, 1942). They show in addition a great deal of inversion hybridity, revealed by the familiar bridge-and-fragment configurations of heterozygous paracentric inversions, and by the presence of heteromorphic chromosome pairs which have been interpreted as the result of heterozygosity for pericentric inversions (J . Walters, 1952). In the course of the previous studies of structural hybridity, occasional cells were noted which showed fragmentation in meiosis occurring in various degrees. A range of breakage has been observed from cells with a single fragment to cells in which not a single intact chromosome is present. As spontaneous fragmentation in meiosis is not common, and has not previously been reported to occur in a structural hybrid, a study was undertaken to determine the extent to which fragmentation occurs in P. calijornica, and whether any relationship can be shown with the other kinds of meiotic irregularity. The results of this study form the subject of the present paper.MATERIALS AND METHODS.-Flower buds of P. calilornica were collected in the field, fixed in Bradley's (1948) fixative, and stored in the fixative under refrigeration. The studies and photomicrographs were made from temporary and permanent iron-acetocarmine smears. In order to investigate the relationship between the extent of translocation heterozygosity and that of breakage, the plants selected for study included four pairing types: the translocation homozygote, with 5[]; an intermediate translocation heterozygote, with 06+2[]2; and two types of extreme heterozygote, with 010 and 06 +04 respectively. In addition to the material collected in the wild, fixations were made from two plants that had been transplanted several years earlier into the Santa Barbara Botanic Garden, to observe possible effects on breakage of growing a plant in other than its native habitat. In five plants, four stages of meiosis (metaphase and anaphase of the first and second divisions) were studied, to 1 Received for publication October 25, 1955. This work has been supported by grants from the Committee on Research of the University of California, Santa Barbara College. Much of the research was done in the laboratory of the Santa Barbara Botanic Garden. The author acknowledges with thanks the support of these institutions, and wishes also to thank Dr. Marta S. Walters for helpful suggestions and for critical reading of the manuscript.2 The symbol 0 means "ring of." determine the frequency and behavior of fragments and related phenomena throughout the course of meiosis. In an additional 11 plants, only anaphase I was studied. One hundred cells of each stage studied in each plant were selected at random. TYPES AND FREQUENCIES OF FRAGMENTs.-Meiotic fr...

Rapid Evolution in Clarkia

“…A number of reports of spontaneous chromosome breakage are now on record for various plant genera including Tradescantia (Giles, 1940;Darlington and Upcott, 1941), Hyacinthus, Tulipa (Darlington and Upcott, 1941), Paris (Haga, 1953), Paeonia (]. L. Walters, 1956), and in hybrids between Allium cepa and A. fistulosum (Emsweller and Jones, 1938). In all instances, save Paeonia, a high level of chromosome breakage was found to be correlated with a visible repatterning of the chromosomes, as observed in pollen mitoses, and in the case of the Allium hybrid, more or less fertile lines with altered chromosome arrangements were obtained by selection from among the progeny of the Fl.…”

The role of U-type exchanges in the differentiation of karyotypes in Najas marina

“…In normal lines, all the fragments formed were small, but those of the deviating lines were of variable size. Such bridge and fragment formation, not compatible with the inversion hypothesis but in agreement with the U-type exchange hypothesis has been observed in various other plant species (MAT- SUURA 1950;HAGA 1953;WALTERS 1956;NEWMAN 1966;STAR 1970;COUZIN and Fox 1973;STUTZ 1976), in certain grasshopper species and in Trirurus vulgaris (LEWIS and JOHN 1966;JOHN 1976).…”

Extensive Chromosome Breakage Occurring Spontaneously in a Certain Individual of Elymus Farctus. (=agropyron Junceum)

“…That this plant is sterile is expected following such a high frequency of aberrations. In Paeonia (MARQUARDT, 1952;WALTERS, 1956) and Scilla (REES, 1952 a ) , the frequency of cells with aberrations did not exceed 20 %. In the interspecific hybrids of Bromus (WALTERS, 1950(WALTERS, , 1952(WALTERS, , 1955(WALTERS, and 1957 and Elymus (HENEEN, 1963 b), and the intergeneric hybrid Elymus arena-riusX Secale cereale (HENEEN, 1963 a ) , however, higher frequencies of spontaneous breakage were found.…”

“…Gene mutations and chromosome breakage are induced in maize following the presence of the recessive gene "sticky chromo-somes" (BEADLE, 1932) or the action of "controlling elements" as in the case of the "Dissociation-Activator" system (MCCLINTOCK, 1956). The rate of spontaneous chromosome breakage was found to vary in the different genotypes of Allium varieties (NICHOLS, 1941), in the F, segregants of a Tradescantia hybrid (GILES, 1940) and in population plants of Paeonia (WALTERS, 1956). ISINC (1962) observed a high frequency of structural changes in aneuploids of Cyrtanthus.…”