Segmentation patterns and mechanisms of genome multiplication in cultured microspores of barley

Abstract

Microspore segmentation in anthers of the barley line C4-13 cultured on a modified N6 medium was followed for 10 days to examine the routes to multicellular structure formation and origin of nonhaploid chromosome numbers. The first division of the uninucleate microspores gave rise to two similar nuclei or a large vegetative and a small generative cell. The two similar nuclei divided independently and both contributed to the formation of multicellular structures. Independent division of the vegetative and generative cell, and division of the vegetative cell alone resulted in two other pathways to multicellular structure formation. Nuclear fusion and endomitosis occurred in some pathways and appeared to be involved in ploidy variation. In addition, a very low frequency of fusion between the nuclei of two microspores was observed. This event may account for the occasional presence of heterozygosity in microspore-derived plants.Key words: barley (Hordeum vulgare), anther culture, androgenesis, ploidy level, nuclear fusion, endomitosis, gene expression.

Initial segmentation patterns of microspores and pollen viability in soybean cultured anthers: indication of chromosome doubling

“…On top of that the increase in the ploidy level occurs at an early stage of culture. Similar findings were also reported by Chen et al (1984) and Henry (1998). The data suggested spontaneous diploidization, which might be caused by nuclear fusion.…”

“…4e and 4f). Similar pictures were presented by Sunderland et al (1974) and Chen et al (1984). Spontaneous chromosome duplication in microspore or anther culture was reported for many species.…”

“…The data suggested spontaneous diploidization, which might be caused by nuclear fusion. According to Chen et al (1984), nuclear fusion in barley usually takes place between the products of the first mitosis in symmetric or asymmetric pollen grains. Therefore, the fusion can occur between identical nuclei or between vegetative and generative nuclei in interphase.…”

Pathways to doubled haploidy: chromosome doubling during androgenesis

“…In barley, the fusion between the nuclei of two microspores was described (Chen et al, 1984b). It was proposed that this phenomenon could be due to incomplete walling during postmeiotic cytokinesis, allowing for the microspores to stay physically connected.…”

“…There are many examples of naturally occurring (tapetum, nuclear endosperm, meiocytes) or experimentally-induced multinucleate cells (Risueño et al, 1968;Nishihama et al, 2001;Park and Twell, 2001) where such a fusion never takes place. Thus, there must be some unknown force that allows for two independent nuclear envelopes to become one (Chen et al, 1984b;González-Melendi et al, 2005;Seguí-Simarro and Nuez, 2007). It has been speculated with a role for actin filaments in driving a nuclear approach , but unfortunately, at this time very little is known about the cellular and molecular mechanisms that drive nuclear fusion in an induced process such as androgenic in vitro development.…”