Organogenesis

What is organogenesis? Describe the protocol for organogenesis. How is it important in plant science and plant biotechnology?

Organogenesis:-

 

       Organogenesis is the process by which cells and tissues are forced to undergo some changes which lead to the production of a unipolar structure namely a shoot primordial or root primordial, whose vascular system is often connected to the parent tissue. Besides adventative, organogenesis may be also “denovo”, i.e. arising as  a new.

       Organogenesis is includes caulogenesis and rhizogenesis. The former refers to the formation of adventitious shoot bud and later is the adventitious root formation, and both led to the formation of new plant let. During organogenesis if roots are first formed, then it is very difficult to induce shoot bud formation in the same callus tissue. On the contrary if the shoots are first formed, it may forms root or may remain rootless condition unless and until the shoot buds are transferred to another medium or hormone less medium or conditions that induce root formation.

       organogenesis can be achieved by two modes-

(i) Emergence of adventitious organs directly from explants. And

(ii) Organogenesis by a callus formation.

       The earliest reports on controlled organogenesis in vitro were by white 1939 who obtained shoot on callus of a tobacco hybrid and by Nobecourt 1939 who observed root formation in carrot callus.

Protocol for organogenesis:-

       Organogenesis includes the sequential steps for the development of plant organs. Here the plant material like tobacco is taken. The steps involved are-

(i) The upper part of the stem of 3-4ft.tall tobacco plants are harvested and cut into 2cm.long internodes segment.

(ii) The above stem pieces are surface sterilized with 70% ethanol for 20 sec. followed by a 15 mins incubation in sodium hypochlorite. Then the stem pieces are washed in sterilized distilled w2ater for 3-4 times.

Flow chart

(iii) The stem pieces are then taken on a petriplate and cut longitudinally. The cut pieces are then incubated in Murashige and Skoog’s solid medium (MS) containing 2mg/lt. IAA and 0.2mg/lt kinetin. The cultures are incubated at 25°c and 16 hours illumination of about 2000lux.

(iv) Within 2-3 weeks callus tissue will appears in the medium and after 6 weeks, it should be subcultured in fresh medium.

(v) The callus structure can be stimulated by transferring tobacco callus to new MS medium with different auxin (IAA) cytokinin ratios. Low auxin concentration and high cytotokinin includes shoot primordial and then transferred into high auxin and low cytokinin containing MS medium to form advent6itious roots.

(vi) Within 6-7 weeks plant lets formed. Such plant lets are removed from the culture vessels and care should be taken not to damage root or shoot system. The plant lets are carefully washed with tapwater to remove the residual agar medium and then they are transplanted into a pot, containing seedling compost. This results in the handeling the plant lets and finally they are transferred to green house condition to develop a mature plant.

Importance of organogenesis:-

       Organogenesis is a wide field of plant science. Hence these importances are vast and varied, which are described below-

(i) With the develo9pment of cellular totipotency and development of methods for regeneration of plant from in vitro cell culture, a large number of plant species, such as medicinal plants, timber yielding plants, horticulturally important plants etc, have been successfully regenerated from callus culture by organogenesis and the reports of regeneration of other plants are still increasing day by day.

(ii) Regeneration of haploid plants from pollen grains and triploid from endosperm cell culture by organogenesis have the potential use in genetics and plant breeding.

(iii) In Orchids, the seeds are minute and cannot germinate. Thus the orchids of commercial interest (eg. Cymbidium) have been successfully propagated through organogenesis.

(iv) Improvement of crop plant through manipulation at the cellular level, such as the vegetative hybridization by the fusion of isolated protoplasts of distantly related plants, the transfer of foreign genetic material in protoplast etc. is possible only when somatic cells are able to give rise to whole plant.

(v) Regeneration of whole plant by organogenesis of special interest in mutagenic studies. The new strength of mutant plants may be obtained through organogenesis.

(vi) Organogenesis is important in freeze preservation of cell culture of many plants and their regeneration when necessary it use for conservation of endangered plant.