Apomixis in ferns. Alternation of generations without syngamy and meiosis

Authors:

• Elżbieta Zenkteler

Abstract

The term apomixis has been used as a general term for asexual form of reproduction including vegetative propagation. In ferns apomixis was first reported 120 years ago, but its widespread has not been established. At the present there occur more than 150 taxa which reproduce apogamously (diploid gametophyte gives rise to a sporophyte without syngamy) or aposporously (unreduced gametophyte is formed from vegetative cells of the sporophyte). The major type of recurrent apomixis in ferns is apogamy accompanied by diplospory which based on modified sporogenesis such one that the chromosome number remains the same in both generations. As in other agamic taxons, apomixis is restricted to highly heterozygous polyploidal ferns and it is assumed that their forms developed as a result of environmental adaptations. This way of reproduction ensures long-term evolutionary success and provides short-term ecological prosperity because it provides genetic stability retaining all the adaptations for survival. Some ferns have fortuitously combined the best of the two models by alternating apomictic with sexual reproduction. The existence of apomictic species provides ideal experimental material for studies to gain understanding of how reproductive events are controlled. By suitable manipulating the cultural conditions in vitro, it has been possible to induce apogamous sporophytes and aposporous gametophytes. Sucrose or byproducts of its metabolism plays a key role in controlling the differentiation pattern of different phases in fern system in vitro. Fundamentally the sporophytic and gametophytic generations are homologous, possessing all information needed to produce gametophytes or sporophytes depending upon the precise nutritive conditions. In this article, we briefly review the current state of knowledge of how apomixis is regulated in ferns and the techniques available for morphogenetic studies on modification in alternation of generation in ferns.