Chromosome elimination in different meristematic regions of hybrids between Hordeum vulgare L, and H, bulbosum L.

Abstract

Cytological observations were made on spike primordia as well as root and leaf meristems of hybrids between Hordeum vulgare and H, bulbosum (2x) to elucidate mechanism of chromosome elimination. High frequencies of cells with micronuclei were observed in spike primordia of the hybrids examined. The average percentages of cells with micronuclei in three different hybrids were 16.8% (R₂5788), 12.9% (S92-201) and 7.9% (S130-200). About 40% of spike primordium cells of R₂5788 had fewer chromosomes than the 14 expected in a diploid hybrid. On the other hand, in root and leaf meristems of R₂5788, percentages of cells with micronuclei were 2.3% and 2.4%, respectively. Also, 94.6% of root meristem cells of R₂5788 had the expected hybrid chromosome number. Thus, chromosome elimination in hybrids between H. vulgare and H. bulbosum appears to be a tissue-dependent phenomenon, perhaps related to the extent of differentiation required.
Disturbances in nuclear division were also examined. Percentages of cells with non-congressed chromosomes at metaphase and lagging chromosomes at anaphase were 15.2% and 20.7%, respectively in spike primordia of R₂5788. These percentages are similar to those of cells with micronuclei in spike primordia of R₂5788. It is suggested that failure of congression of some chromosomes during prometaphase is the main mitotic disturbance leading to chromosome elimination.