The following points highlight the top eight types of tissue culture. The types are: 1. Seed Culture 2. Embryo Culture 3. Meristem Culture 4. Bud Culture 5. Callus Culture 6. Cell Suspension Culture 7. Anther Culture 8. Protoplast Culture.
Type # 1. Seed Culture:
Seeds may be cultured in vitro to generate seedlings or plants. It is the best method for raising the sterile seedling. The seed culture is done to get the different kinds of explants from aseptically grown plants which help in better maintenance of aseptic tissue.
Type # 2. Embryo Culture:
Embryo culture is the sterile isolation and growth of an immature or mature embryo in vitro with the goal of obtaining a viable plant. In some plants seed dormancy may be due to chemical inhibitors or mechanical resistance, structures covering the embryo. Excision of embryos and culturing them in nutrient media help in developing viable seedlings.
Embryo developed from wide hybridisation between two different species may not mature fully due to embryo-endosperm incompatibility. So, the isolation and culture of hybrid embryos prior to abortion help in overcoming the post-zygotic barrier and production of interspecific or inter-generic hybrids.
Type # 3. Meristem Culture:
The apical meristem of shoots of angiosperms and gymnosperms can be cultured to get the disease free plants. Meristem tips, between 0.2-0.5 mm, most frequently produce virus-free plants and this method is referred to as meristem-tip culture.
This method is more successful in case of herbaceous plants than woody plants. In case of woody plants, the success is obtained when the explant is taken after the dormancy period is over. After the shoot tip proliferation, the rooting is done and then the rooted plantlet is potted.
Type # 4. Bud Culture:
Buds contain quiescent or active meristems in the leaf axils, which are capable of growing into a shoot. Single node culture, where each node of the stem is cut and allowed to grow on a nutrient media to develop the shoot tip from the axil which ultimately develops into new plantlet. In axillary bud method, where the axillary buds are isolated from the leaf axils and develop into shoot tip under little high cytokinin concentration.
Type # 5. Callus Culture:
Callus is basically more or less un-organised dedifferentiated mass of cells arising from any kind of explant under in vitro cultural conditions. The cells in callus are parenchymatous in nature, but may or may not be homogenous mass of cells. They are meristematic tissue, under special circumstances they may be again organised into shoot primordia or may develop into somatic embryos.
The callus tissue from different plant species may be different in structure and growth habit. The callus growth is also dependent on factors like the type of explant and the growth conditions. After callus induction it can be sub-cultured regularly with appropriate new medium for growth and maintenance.
Type # 6. Cell Suspension Culture:
The growing of individual cells that have been obtained from any kind of explant tissue or callus referred to as cell suspension culture. These are initiated by transferring pieces of tissue explant/callus into liquid medium (without agar) and then placed them on a gyratory shaker to provide both aeration and dispersion of cells. Like callus culture, the cells are also sub-cultured into new medium.
Cell suspension cultures may be done in batch culture or continuous culture system. In the later system, the culture is continuously supplied with nutrients by the inflow of fresh medium with subsequent draining out of used medium but the culture volume is constant. This culture method is mainly used for the synthesis of specific metabolite or for biomass production.
Type # 7. Anther Culture:
An important aspect of plant tissue culture is the haploid production by another culture or pollen culture which was first established by Guha and Maheswari (1964, 1966) in Datura.
During the last few decades, much progress has been made in different crops like rice, wheat, maize, mustard, pepper and others. The anthers bearing the uni-nucleate microspores are selected and allowed to grow in medium to produce callus from the pollen mass.
Then the triggering of these androgenic calli is directed to produce the embryos and haploid plants are developed from these androgenic embryos. The anther culture can be done with the isolated anthers on solid medium where anther wall will break open and the androgenic calli will be formed from the pollen.
In pollen culture, microspores of uni-nucleate stage are collected in liquid media and can be grown in suspension culture. In suspension, the uni-nucleate pollens may give rise to calli mass or the globular mass from which the plants can be raised either through embryogenic or organogenic pathway.
Type # 8. Protoplast Culture:
It is the culture of plant protoplasts i.e., culture of cells devoid of cell wall. Isolated protoplasts are usually cultured in either liquid or semisolid agar media plates. Protoplasts are isolated from soft parenchymatous tissue by enzymatic method and then viable protoplasts are purified and cultured.
The protoplast culture is aimed mainly to develop genetically transformed plant where the transgenic is put successfully within the plant protoplast and the transgenic plant is regenerated from that transformed protoplast. Another aspect of protoplast culture is somatic hybridization of two plant species through protoplast fusion.