1. Topic : Organogenesis in Agriculture Biotechnology
Presented by ;
Akshat Raj
B.Sc. Agriculture
2nd Year
Presented to ;
Mr. T. Ahmad (HOD Agriculture)
DATE: 21/09/2021
3. Introduction…
Various new plants are being developed by the help of plant parts (explant) in the laboratory under
human care and in the presence of all the suitable environmental conditions.
The term that is given to such procedure is called as ‘plant tissue culture’(PTC). By this technique
new cells, tissues and organs are developed under controlled conditions in the presence of various
medium.
In this , small pieces of viable tissues called ‘explant’ are isolated from parent plant and grown in a
definite nutritional medium for very long period of time under aseptic conditions.
Depending upon the source of ‘explant’ it can be named as follows :
1. Anther - Anther Culture
2. Pollen - Pollen Culture
3. Cell - Cell Culture
4. Protoplast - Protoplast Culture
5. Callus - Callus Culture
4. General techniques of ‘plant tissue culture’ involve four major stages. They are :
1) Initiation of culture
2) Multiplication or sub-culture
3) Development and differentiation ( ORGANOGENESIS )
4) Hardening
ORGANOGENESIS
Organ Genesis ( means formation)
flowers
roots
stem
Definition : It can be defined as the development of organs like flowers , roots and shoots either
directly from an ‘explant’ or from the ‘callus culture’.
Development of plant organs is initiated from the meristematic cells. The organs like flowers,
and lateral organs are initiated by SAM ( Shoot Apical Meristem) and roots and its parts are developed from
RAM (Root Apical Meristem).
The cells, when induced in-vitro, give rise to whole plants.
5. Methods of Organogenesis
It include certain procedures or techniques that led to the formation of various adventitious organs ( organs
that don’t develop either from radicle or plumule).
It includes : (A). Callus Culture (B). From an explant
(A). CALLUS CULTURE (Indirect Organogenesis)
Plant regeneration from cultured explant involves the initiation of basal callus and then shoot bud
differentiation.
Establishment of callus growth with subsequent organogenesis has been obtained from many species of
plants and from numerous explants viz. cotyledons hypocotyl, stem, leaf, shoot apex, root, young
inflorescence, flower petals, petiole, embryos etc. cultured ‘in vitro’.
7. Factors that favor better organogenesis through callus culture
For any given species or variety, a particular explant may be necessary for successful plant regeneration.
Explant from both mature and immature organs can be induced to form callus and then plant regeneration.
However there are certain factors that favor better development. They are :-
1. Explants with mitotically active cells are generally good for callus initiation.
2. Presence of vascular tissue in explant is favorable to callus growth.
3. The increased cell number present in bigger explants increases the probability of obtaining a viable culture.
4. Meristematic tissues or organs like shoot tip, lateral bud, inflorescence, rachis, leaf, petiole, root should be
selected in preference to other tissues because of their clonal properties, culture survival growth rates and
totipotency in vitro.
8. (B). FROM AN EXPLANT ( Direct Organogenesis)
Somatic tissues of certain higher plants are capable of
regenerating adventitious plants.
Induction of adventitious shoots directly on roots, leaves, bulb
and other organs of intact plants is a common method of
propagation.
This is suitable for various species of herbaceous plants in
culture techniques.
In this method generally buds are taken for getting a new plant
and it is done by adding more cytokinin into the culture
medium that promotes the profuse development of shoot from
the bud.
This technique will give the idea of ‘totipotency’ that a cell
have the ability of developing into a new plant.
As it is understood that each cell of a plant is developed from
the zygotic cell. The only thing is the reactivation of that genes
that are concerned with embryonic phase of development.
9. Steps of Organogenesis
Process of organogenesis basically includes two steps:
Caulogenesis
Rhizogenesis
1. Caulogenesis:
Induction of adventitious shoot buds from the cultured tissues is known as ‘caulogenesis’.
This was usually made after the formation of callus in the culture condition or
directly from the explant which was placed on the medium.
It is promoted by the addition of ‘cytokinin’ in the medium.
2. Rhizogenesis
Induction of adventitious roots from the cultured tissue is known as ‘rhizogenesis’.
It is induced or formed only after the formation of shoot in plant tissue culture method.
It is promoted by the addition of ‘auxin’ in the medium.
10. Chemical regulation of organogenesis
In 1944, Skoog showed chemical supplements in media can regulate the process of organogenesis.
AUXIN:
It promotes the growth of root and inhibit the growth of shoot and it also facilitate the cell division.
It induce the cell elongation and formation of callus in culture.
Plant produce natural types of auxin like Indole butyric acid (IBA) and Indole-3-acetic acid. These
are produced by roots of plants.
Other factors that control the formation of roots are mineral, salt, sugar, temperature
and light.
Phlorogucinol + Indole butyric acid are more affective in promoting root formation.
11. CYTOKININ:
It induces the formation and elongation of shoot.
It also promotes RNA synthesis and stimulate protein and enzyme
activities of tissues.
For root initiation: concentrationAuxin > concentration cytokinin
For shoot initiation: concentration cytokinin > concentration auxin
12. Factors affecting Organogenesis
The climatic conditions, donor conditions of the plant, the age and physiological
state of the parent plant contribute to the success of organogenesis in cell culture.
Two modes of cell culture are generally used for organogenic path :-
1. The cultivation of cell clusters on a solid medium.
2. The cultivation of cell suspensions in liquid medium.
Growth regulator concentration in the culture medium is critical for morphogenesis.
Auxin at a moderate to high concentration is the primary hormone used to produce
callus. Often 2,4-D, a very potent auxin is used alone to initiate callus.
In some species a high concentration of auxin and a low concentration of cytokinin
in the medium promotes abundant cell proliferation with the formation of callus.
Callus may be serially sub-cultured and grown for extended periods, but its
composition and structure may change with time as certain cells are favored by the
medium and come to dominate the culture.
13. Cytokinin (adenine or kinetin) in the medium leads to the promotion of shoot bud
differentiation and development.
IAA or IBA auxins alone or in combination with a low concentration of cytokinin are
favorable for induction of root primordia.
Thus, root shoot differentiation is a function of quantitative interaction between auxin
and cytokinin.
Increased level of phosphate in the medium is reported to counteract the inhibitory
effect of auxin and promotes bud formation in the absence of cytokinin.
14. Light intensity plays an important role in organogenesis. High light intensity has been shown
to be inhibitory for shoot-bud formation.
The quality of light also influences organogenesis. Blue light promotes shoot-bud
differentiation in tobacco callus while red light stimulates rooting.
Temperature also affects the callus growth and differentiation. Increase in temperature up to
33° C may be associated with rise in the growth of callus but for shoot-bud differentiation, a
lower temperature (18° C) may be optimal.
The physical state of the medium also influences shoot-bud differentiation. A medium
solidified with agar favors bud formation although there are some reports about the
development of leafy shoot buds on cultures grown in a liquid medium.
