Irregular microspore formation in Datura innoxia and its relevance to anther culture

Meiotic irregularities in pollen mother cells of Datura innoxia lead to the formation of diploid (uninucleate) spores, and to multinucleate spores containing 2, 3 or 4 haploid nuclei. At the free microspore stage, irregular spores form three distinct size-classes having mean diameters of 46 (class II), 52 (III) and 64 (IV) ~tm, compared with 36 ~tm (I) for regular haploid spores. At the beginning of flowering, irregular spores account for about 0.8%(400-450) of the total pollen per anther, but the frequency increases with plant age, and towards the end of flowering, it may be as high as 8~ Irregular spores give rise either to non-haploid pollen grains (2 n, 3 n, 4 n) consisting of one generative and one vegetative nucleus, or to multinucleate pollen grains containing several generative and vegetative nuclei which may be of the same or of different ploidy. In cultured anthers, irregular spores or young pollen grains derived from them, participate in embryogenesis and give rise to non-haploid proembryoids. These are seen as contributing to the complement of non-haploid plants that ultimately emerge from the anthers. Such plants will be heterozygous in contrast to non-haploid plantlets generated from haploid pollen by nuclear fusion