The role of nuclear fusion in pollen embryogenesis of Datura innoxia Mill.

Abstract

If anthers of Datura innoxia containing microspores are cultured at 28° C for 24 h, two forms of haploid pollen grains are produced; one with typical unequal generative and vegetative nuclei (A), and the other with equal vegetativetype nuclei (B). The A form predominates. After 24 to 72 h in culture, three embryogenic events ensue; 1) division of the vegetative cell in A grains accompanied by rapid degeneration of the generative cell, 2) simultaneous or independent mitosis of the nuclei in B grains, and 3) simultaneous mitosis of both the generative and vegetative nuclei in A grains following two successive cycles of DNA synthesis in the generative nucleus, but only one in the vegetative nucleus (C). The endoreduplicated generative nucleus gives rise to diplochromosomes which it is postulated divide on a common spindle together with the vegetative chromosomes to yield a 3n proembryoid. In other C grains, simultaneous mitosis of an endoreduplicated generative nucleus and two vegetative daughter nuclei can occur. Nuclear fusion in these grains is envisaged as leading to a 4n proembryoid. Diploid proembryoids probably arise by nuclear fusion in A or B grains. At plantlet emergence, mainly n and 2n plantlets are obtained. Higher ploidy proembryoids fail to develop probably as a result of competitive influences.Similar embryogenic events occur in cultures initiated at the stages of the first pollen mitosis and young pollen grains, but C embryogenesis predominates. Competition from lower ploidy embryoids is minimised and 3n, 4n and even 6n plantlets are obtained.

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

“…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.…”

Study of androgenesis and spontaneous chromosome doubling in barley ( Hordeum vulgare L.) genotypes using isolated microspore culture

“…C-mitosis, such as occurs during colchicine treatment, may result in a simple restitution nucleus with a doubled chromosome number. In Datura, it was proposed that both endoreduplication and nuclear fusion were involved in chromosome doubling and that the combination of both methods could explain the ploidy levels obtained, which were higher than diploid (Sunderland, 1974;Sunderland et al, 1974;Seguí-Simarro and Nuez, 2008). Nuclear fusion was described as occurring when two nuclei synchronously entered into division, formed a common metaphase plate and spindle and resulted in two nuclei, each with more than one set of chromosomes (Sunderland, 1974).…”

Ploidy levels in Citrus clementine affects leaf morphology, stomatal density and water content

“…Anther culture has been already engaged for the production of androgenic haploids (Germanà et al 2005). Sunderland et al (1974) demonstrated the origin of triploids and tetraploids from anther culture. Single nucleus of an embryogenic grain divides asymmetrically into a generative and a vegetative nucleus.…”