[Meiotic restitution in amphihaploids in the tribe Triticeae]

In haploid and diploid organisms of the plant kingdom, meiotic division of diploid cells proceeds in two consecutive stages, with DNA replicating only once. In amphihaploids (interspecific or iontergeneric hybrids), where homologs are absent, the reduction of the chromosome number does not occur, meiosis is abnormal, and the plants are sterile. Gamete viability in F1 hybrids is ensured by a single division when chromosomes are separated into sister chromatids in either the first or the second division. Such gametes ensure partial fertility of amphihaploids, thereby facilitating their survival and stabilization of the polygenome. The frequency of the formation of viable gametes varies from a few cases to 98.8% in different anthers of the hybrids. Here, studies on the cytological mechanisms and genetic control of chromosome unreduction or restitution in different amphihaploids of the tribe Triticeae are reviewed. The current notions on the control of formation of restitution nuclei based on the principles of a prolonged metaphase I and different types of meiocytes. The main terms used for systematization of restitution mechanisms are first-division restitution (FDR), single-division meiosis (SDM), and unreductional meiotic cell division (UMCD). It has been assumed that archesporial cells of remote hybrids may have two cell division programs, the meiotic and the mitoyic ones. The possible approaches to the analysis of the genetic control of chromosome restitution in amphihaploids are discussed.