Introduction of plant tissue culture

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2. Background-
 For thousands of years man has been dependent on plants
for food, shelter, medicine and many other purposes.
 The latest advances in plant biotechnology provide potential to
make improvements much more quickly than by conventional
plant breeding. Studies on all aspects of plant development and
multiplication in whole plants are often complicated by
interactions between the various processes that underlie growth
and development. It is, therefore, desirable to simplify matters
so that controlling influences can be easily identified and
studied.
 This can be done by isolating and culturing parts of the plants
in vitro. It is also being applied to study basic aspects of plant
growth and development.
 The discovery of the first cytokinin (kinetin) is based on plant
tissue culture research.

3. .
 Currently, the most popular commercial application of plant
tissue culture is clonal propagation of disease-free plants. In
vitro clonal propagation, popularly called micropropagation,
offers many advantages over the conventional methods of
vegetative propagation: (1) many species (e.g. palms, papaya)
which are not amenable to in vivo vegetative propagation
are being multiplied in tissue cultures, (2) the rate of
multiplication in vitro is extremely rapid and can continue
round the year, independent of the season.
 An important contribution made through tissue culture is the
revelation of the unique capacity of plant cells, called “cellular
totipotency”. it forms the backbone of the modern approach to
crop improvement by genetic engineering.
 Plant regeneration from cultured cells is proving to be a
rich source of genetic variability, called “somaclonal
variation”. Several somaclones have been processed into new
cultivars.

4. . Regeneration of plants from microspore/pollen provides the most
reliable and rapid method to produce haploids, which are extremely
valuable in plant breeding and genetics. With haploids, homozygosity
can be achieved in a single step, cutting down the breeding period
to almost half. This is particularly important for highly heterozygous,
long-generation tree species.
 Pollen plants also provide a unique opportunity to screen gametic
variation at sporophytic level. This approach has enabled selection of
several gametoclones, which could be developed into new cultivars.
 Triploid cells of endosperm are totipotent, which provides a direct and
easy approach to regenerate triploid plants difficult to raise in vivo.
 The earliest application of plant tissue culture was to rescue hybrid
embryos and the technique became a routine aid with plant breeders to
raise rare hybrids, which normally failed due to post-zygotic sexual
incompatibility.

5. Terms commonly used in plant tissue culture
 Plasticity: Plants due to their long-life cycle and lack of mobility have
developed greater capacity to survive extreme conditions. Many of the
processes involved in plant growth and development adapt to environmental
conditions. This plasticity allows plants to alter their metabolism, growth
and development to best suit their environment.
 When plant cells and tissues are cultured in vitro, they generally exhibit a
very high degree of plasticity, which allows one type of tissues or organs to
be initiated from another type under the influence of chemical stimuli.
 In this way, whole plants can be subsequently regenerated. For example,
embryos may be developed in vitro from somatic cells and haploid cells, as
well as from normal zygote and all these, in turn, could develop into whole
plants.
 Totipotency: Totipotency is the potentiality or property of a cell to produce
a whole organism or whole parent plant in the presence of correct physical
and chemical stimulus.

6. .
 Recalcitrant: The opposite of totipotency is recalcitrant. An explant is said
to be recalcitrant if it is difficult to give rise to organism or plant.
 Explant: A plant organ or piece of tissue used to initiate a culture.
 Culture: Growing cells, tissues, plant organs, or whole plants in nutrient
medium, under aseptic conditions e.g. cell culture, embryo culture, shoot-tip
culture, anther culture.
 Contaminants: In tissue culture it refers to the micro-organisms (Bacteria,
Fungi), which may inhibit the growth of cells or tissues in culture.
 Node: A region on the stem from which a leaf bearing an axillary bud
arises.
 Morphogenesis: The anatomical and physiological events involved in the
growth and development of an organism resulting in the formation of its
characteristic organ and structures, or in regeneration.
 Meristem: A localized group of actively dividing cells, from which
permanent tissue system i.e. root, shoot, leaf and flower are derived. Apical
meristem is located at the apices of main and lateral shoots.

7. .
 Meristematic: having the characteristics of a meristem, especially high
mitotic activity.
 Meristemoid: A localized group of meristematic cells that arise in the
callus and may give rise to roots and or shoots.
 Regeneration: In tissue culture, a morphogenetic response that results in
the formation of new organs, embryos or whole plants from cultured
explants.
 Dedifferentiation: The phenomenon of mature cells reverting to
meristematic state to produce callus is dedifferentiation. Dedifferentition is
possible because the non-dividing quiescent cells of the explant, when
grown in a suitable culture medium revert to meristematic state.
 Redifferentiation: The ability of the callus cells to differentiate into a plant
organ or a whole plant is regarded as redifferentiation.
 Adventitious: Developing from unusual points of origin, such as shoots or
roots arising from a leaf or stem tissues other than the axils or apex; and
embryos from any cell other than the zygote.
 Determined: Cells that are committed to a particular pathway of
development or differentiation but which have yet to overtly express this
pathway.

8. .
 Heterotrophic: Dependent on an external energy source; not self-
reliant compare to autotrophic.
 Ploidy: Term used to describe the number of genomes present in the
nucleus of a cell or plant.
 Polarity: In plants, like in animals, the axes appear very early in
development and mostly they are polar in nature. The gradation or
change in character occurs along the axis from one end to the other
and the condition is referred as ‘polarity'. It is visible as
morphological differentiation during the development of shoots and
roots or is invisible, physiological effect which is expressed during
reactivity of cells, tissues and organs in determining cell division and
cell growth, and to geotropic or phototropic stimuli. The entire plant
is bipolar in nature consisting of two ends, ‘plumular' end (where the
shoots develop) and ‘radicular' (where the roots develop). Besides,
there are two other terms, ‘distal' and ‘proximal'. Distal refers to the
part of the plant which is furthest from the original point of
attachment i.e. the tip of the leaf or shoot or root, while proximal
means nearest to the point of attachment.

9. Applications of Plant Tissue Culture-
 Fundamental biological studies: These can provide a simple, easily
manipulated system for investigating a range of phenomena, e.g. the use of cell
suspension cultures for studies of cell division.
 High value biochemicals: Many of the natural plant metabolites are required
by the pharmaceutical and cosmetic industries. Since environmental conditions
can be tightly controlled in vitro, a constant output might be maintained without
seasonal variation. Moreover, simplicity of cell culture may allow high yields to
be produced at low cost.
 Plant multiplication by micropropagation: Micropropagation offers a rapid
means of vegetative (asexual) multiplication. It is important in those plants
which are otherwise difficult to propagate, have a high value or where speed of
propagation is important. It can also help to raise disease-free stock of a crop by
apical meristem culture where the entire plant is infected with pathogenic
bacteria or viruses.
 Embryo rescue: Hybrid embryos, formed by the fusion of gametes from distant
relatives, frequently abort naturally because the endosperm is not compatible
with embryo. Under in vitro conditions, in the presence of correct nutritional
medium, these embryos can be developed and form a plant.

10. Applications of Plant Tissue Culture
 Pollen Culture: The pollen of many species can be induced to develop into entire plant
without participating into fertilization process. These plants contain single set of
chromosome, as that of gametes, and are haploid in nature. The chromosome set of these
haploids can be diploidized by mutagenic treatment like, colchicine, to develop
homozygous diploid lines or pure breeding lines. This technique is very useful in case of
highly heterozygous tree species with long generation cycle.
 Production of plants with novel characteristics: The somaclonal or gametoclonal
variations induced in in vitro cultures can be utilized to raise new improved varieties
which may have of commercial value such as, new flower color, big canopy plants, large
sized grains etc.
 Production of transgenic plants: Characteristics like, insect resistance, that could not
be achieved by conventional plant breeding methods, can be transferred from one plant
species to another by Agrobacterium- mediated gene transfer or by gene transfer methods
like, particle gun method (biolistics), electroporation, microinjection and polyethylene
glycol-mediated gene transfer.
 Protoplast fusion: The protoplasts can be fused to form somatic hybrids. Such fusion
products are the result of the union of two or more protoplasts from similar or dissimilar
parents.

11. THANKS