Anther, Pollen and Ovule Culture (Haploid Production)
An important aspect of plant breeding is the induction of maximum genetic variability of germplasm sources to secure a wider scope for selection and introduction of better trait qualities in existing crop species. Plant breeders have worked extensively to obtain haploids either in vitro or in vitro. In nature, haploids arise as a result of parthenogenesis and these plants rarely produce characters of the male parent.
In angiosperms the haploid or Gametophytic phase is extremely brief and is extremely brief and is represented by pollen grains in anther and one cells in the embryo sac of the ovule. A typical anther in cross section shows two anther lobes and each lobe possesses two pollen two pollen sacs. During microsporogenesis, pollen mother cell (PMC) inside the pollen sac form pollen tetrad by meiosis. In each pollen tetrad, four pollens are held together temporarily by their callose wall. Pollens separate as descrete unit by dissolution of callose wall. Each pollen possesses an unique genome where every gene is present as a single copy.
Exploitation of this unique genetic unit and the totipotency of the plant cell is the basis of anther or pollen culture for the production of haploid plants. On the other hand, egg cell produced within the ovule is very difficult to separate from complex tissue integration. In culture, the anther swells and dehisces along its upper margin, lengthwise. This phenomenon helps to expose the pollen grain. Alternatively, huge amount of pollen grains can be isolated manually and can be cultured aseptically very easily. Therefore, pollen is more suitable material than egg cell for the production of haploid.
The development and production of haploid plant in vitro is very important for the study of fundamental and applied aspects of genetics in the higher plants. Production of homozygous diploid by doubling the chromosome number of haploid in vitro makes a pure line in single step and such homozygous pure line is of great importance in plant breeding.
Anther culture is technique by which the developing anthers at a precise and critical stage are excised aseptically from unopened flower bud and are cultured on a nutrient medium where the microspore within the cultured anther develop into callus tissue or embryoids that give rise to haploid plantlets either through organogenesis or embryogenesis.
Pollen or microspore culture is an in vitro technique by which the pollen grains, preferably at the uninucleated stage, are squeezed out aseptically from the intact anther and then cultured on nutrient medium where the microscope, without producing male gametes, develop into haploid embryoids or callus tissues that give rise to haploid plantlets by embryogenesis or organogenesis.
Ovule culture is an elegant experimental system by which ovules are aseptically isolated from the ovary and are grown aseptically on chemically defined nutrient medium under controlled conditions.