In 1953 Tulecke discovered that haploid tissue (i.e. tissue composed of cells having half the chromosome number that is characteristic of a species), could be produced by the culture of Ginkgo pollen. Little notice was taken of his work until Guha and Maheshwari (1964, 1967) managed to regenerate haploid plants from pollen of Datura innoxia by culturing intact anthers. Since then a great deal of research has been devoted to the subject.
The basis of pollen and anther culture is that on an appropriate medium the pollen microspores of some plant species can be induced to give rise to vegetative cells, instead of pollen grains. This change from a normal sexual gametophytic pattern of development into a vegetative (sporophytic) pattern, appears to be initiated in an early phase of the cell cycle when transcription of genes concerned with gametophytic development is blocked and genes concerned with sporophytic development are activated (Sunderland and Dunwell, 1977). The result is that in place of pollen with the capacity to produce gametes and a pollen tube, microspores are produced capable of forming haploid pro-embryos (somatic embryos formed directly from the microspores), or callus tissue. The formation of plants from pollen microspores in this way is sometimes called androgenesis. Haploid plants are more readily regenerated by culturing microspores within anthers than by culturing isolated pollen. The presence of the anther wall provides a stimulus to sporophytic development. The nature of the stimulus is not known but it may be nutritional and/or hormonal. Embryogenesis has only been induced from isolated pollen of a very small number of plants.
The number of plants species from which anther culture has resulted in haploid plants is relatively few. It comprised about 70 species in 29 genera up to 1975 (Sunderland and Dunwell, 1977) and 121 species or hybrids in 20 families by 1981-1982 (Maheshwari et al., 1982) and by now, very many more. The early stages of embryogenesis or callus formation without plant regeneration have been obtained in several other kinds of plants. Fifty- eight per cent of the reports of embryogenesis or plant regeneration in Maheshwari et al. (1982) was attributable to species within the family Solanaceae. Species in which haploid plants can be regenerated reliably and at high frequency remain a comparatively small part of the total. They again mainly comprise Solanaceous species such as Datura, Nicotiana, Hyoscyamus, Solanum and some brassicas.
For further information on pollen and anther culture, which is outside the scope of the present book, the reader should consult the following books or review articles: Dunwell (1985); Foroughi-Wehr and Wenzel (1989); Giles and Prakash (1987); Heberle-Bors (1985); Hu and Yang (1986); Jain et al. (1996); Keller and Stringham (1978); Maheshwari et al. (1980, 1982); Morrison and Evans (1988); Nitsch (1977, 1981; 1983); Palmer et al. (2005);
Raghavan (1990); Reinert and Bajaj (1977); Sangwan and Sangwan-Norreel (1990); Vasil (1980c).
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