Identification of the chromosomes showing neocentric activity in rye

Abstract

Chromosomes showing neocentric activity were identified with the aid of the C-banding technique in an inbred line of rye, 1940-129 of cv. 'Stålråg'. The frequency of cells with neocentrics varied from 34 to 35.7% at first anaphase, and from 32 to 68% at second metaphase. In most cells only one chromosome showed the activity. It always belonged to the group 4-5-6R, and in cells where individual identification of chromosomes was possible the activity was invariably located at the telomere of the arm 4RS. When in rare cases two or three chromosomes were active, one chromosome again belonged to the group 4-5-6R, the other was identified in four cells as a member of the group 2-3-7R, but it is possible that all the telomeres with a prominent C-band can occasionally show the activity. It is assumed that certain telomeric regions remain in the active state at both meiotic divisions and offer secondary accumulation sites for kinetochoric proteins.

Independently Regulated Neocentromere Activity of Two Classes of Tandem Repeat Arrays

“…Knobs in interstitial positions appear to have evolved many times in nature (Rodionov, 1999), and in general they tend to be highly polymorphic (Döbel et al, 1973;Vosa, 1973;Árnason, 1974;Marks and Schweizer, 1974;Lelley et al, 1978;Belyayev et al, 1995). Neocentromeres have been observed in at least eight plant species, including the "enormous stretching of the chromatin" in Pennisetum orientale and the "fantastically elongated" chromosomes in Elymus wiegandii (Vilkomerson, 1950;Walters, 1952;Hayman, 1955;Zohary, 1955;Bosemark, 1956;Vardhan and Lakshmi, 1983;Viinikka, 1985). In maize, rye, Pennisetum (millet), and Festuca (meadow fescue), the sites of neocentromere activity appear to be knobs.…”

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“…In rye, several results were presented demonstrating neocentric activity of chromosomes (KATTER-MANN 1939;PRAKKEN and MONTZING 1942;OSTER-GREN and PRAKKEN 1946;REES 1955;HEYWARD 1962;VIINIKKA 1985). This phenomen had been described so far as diffused or terminalized action of the centromere in first and second meta -anaphase of meiosis in individuals with an abnormal genotype.…”

“…On the other hand, neocentric activity of telomeres is obviously based on a specific chromatin structure which is controlled by a polygenic complex (HEYWARD 1962). Neocentrics in rye were localized by VIINIKKA (1985) exclusively at the telomeres, most frequently at the chromosome arms 4Rp, 5Rp and 6Rp.…”

Movement ability of rye terminal neocentromeres

“…The repetitive subtelomeric sequences pSc34, pSc74 and pSc200 underlie the neocentromeres (Manzanero and Puertas, 2003). The number of chromosomes with neocentromeres, as well as the intensity of their activity, varies among individuals and cells within the same individual (Viinika, 1985;Viinika and Kavander, 1986). Hayward (1962) reported that the genetic control of these neocentromeres is polygenic.…”