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

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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 1st division of the uninucleate microsphores gave rise to 2 similar nuclei or a large vegetative and a small generative cell. The 2 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 2 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 2 microspores was observed. This event may account for the occasional presence of heterozygosity in microspore-derived plants.