Replicon size, rate of DNA replication, and the cell cycle in a primary hexaploid triticale and its parents

Abstract

It has been previously shown that, surprisingly, DNA synthesis in a hexaploid triticale resembled that in a hexaploid bread wheat much more than in a diploid rye cultivar with respect to (i) replicon size, (ii) rate of DNA replication fork movement, and (iii) the degree of synchrony of replicon activation. The wheat and rye cultivars were not the parents of the triticale, but it was suggested that perhaps in a triticale nucleus, DNA replication in chromosomes from rye may be governed to be similar to that of wheat chromosomes in the wheat parent. The present work aimed to test this hypothesis using DNA fibre autoradiography to study DNA replication in root meristem cells of a diploid rye, a tetraploid wheat, and the primary allohexaploid triticale derived from them. The results, which again showed striking differences between rye, wheat, and triticale, did not substantiate the above-mentioned hypothesis. Instead, factors in the hybrid triticale may interact to impose a new common replicon size, a new common rate of replication, and, a more synchronous pattern of activation of replication, all different from those found in either parent. These results provide evidence for the existence of an important genetic mechanism that can act to synchronize the developmental behaviour of different ancestral diploid genomes in allopolyploids. Variation in the expression of this mechanism may have important agronomic and evolutionary consequences. Perhaps improvement in nuclear stability and in kernal type achieved in triticale breeding involves selection for greater synchrony of replicon activation during DNA synthesis.Key words: cell cycle, DNA replication, replicon, S phase, triticale.