Heterochromatin, aberrant endosperm nuclei and grain shrivelling in wheat-rye genotypes

Abstract

SUMMARYEvidence is presented leading to the conclusion that there is, in wheat-rye genotypes, a causal link first, between the presence of late replicating segments of heterochromatin on rye chromosomes and the occurrence of chromosome bridges at anaphase and of other aberrant nuclei in coenocytie endosperm, and second, between the frequency of occurrence of aberrant nuclei in young endosperms and the degree of grain shrivelling at maturity. Bridges in coenocytic endosperm of wheat-rye genotypes are caused at anaphase by the failure of rye chromosomes to separate at the telomeres where late replicating DNA is known to be located. The frequency of occurrence of aberrant nuclei in endosperms of the seven disomic chromosome addition lines of King H rye to Holdfast wheat fixed at the end of the coenocytic stage is significantly lower in three addition lines lacking a large telomeric block of terminal heteroehromatin on one arm (due to its deletion) than in the remaining four addition lines without deletions of terminal heteroebromatin. Evidence is presented showing a significant positive correlation between the proportion of aberrant nuclei in endosperms of six hexaploid triticales during the first 4 days after pollination, and the degree of grain shrivelling scored at maturity. It is concluded that the reduction or elimination of segments of late replicating DNA from rye chromosomes should be a major object in the breeding of economically useful triticales, and the means of achieving this goal are discussed.

The quantitative relationship between telomeric heterochromatin and secalin synthesis in Secale cereale L.

“…The detrimental influence of rye telomeric heterochromatin on the development of triticale led Bennett (1977) to suggest that the selection of lines containing `modified' rye chromosomes could be beneficial in the breeding of superior lines of this species . An increase in aberrant endosperm nuclei resulting in a corresponding increase in grain shrivelling has been correlated to the amount of telomeric heterochromatin present in the rye genome (Bennett, 1977) ; . It has been recently demonstrated that a loss of approximately 90% of the telomeric heterochromatin from chromosome 6RS of triticale cv .…”

“…In genlines of rye (Secale cereale L.) (Lelley et al ., 1978 ; eral, increasing the amount of rye telomeric heter- Giraldez et al ., 1979) . The nature of this variation is ochromatin has a detrimental influence on develstill not understood and continues to attract considopment of the kernel (Merker, 1976 ;Bennett, erable interest . It has recently been demonstrated 1977 ; Bennett & Gus-that the telomeric heterochromatin of rye consists tafson, 1982) .…”

Backcrossing to increase meiotic stability in triticale

“…In triticale cells, the rapid cell cycle of rye may result in insufficient time for chiasmata formation in the chromosomes of wheat (Bennett, 1977). This hypothesis was first suggested with regard to triticale hexaploids by Tsuchiya (1970) and to octoploids by Pieritz (1970).…”

Chromosomal Replicons of Higher Plants

“…A change in these properties, however, nay be deleterious particularly at certain developmental stages. In triticaie, for example, deleterious effects are seen as shrivelled grains and aberrant endosperm nuclei (Bennett, 1977;. Bennett (1977; and Francis et al (1985) postulate that these effects result from the compliance of the rye chromosomes (S phase of 6.6 hours) to a S phase of 4.7 hours in triticale leaving insufficient time for the replication of late replicating heterochromatin in the rye chromosomes.…”

“…In triticaie, for example, deleterious effects are seen as shrivelled grains and aberrant endosperm nuclei (Bennett, 1977;. Bennett (1977; and Francis et al (1985) postulate that these effects result from the compliance of the rye chromosomes (S phase of 6.6 hours) to a S phase of 4.7 hours in triticale leaving insufficient time for the replication of late replicating heterochromatin in the rye chromosomes. , 1985), is currently viewed by the authors as a by-product of genomic rearrangements that precede the differentiation of vascular parenchyma cells.…”