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CONSERVATION
OF PLANT SPECIES IN GERMPLASM BANKS
C Kameswara Rao
Foundation
for Biotechnology Awareness and Education,
Tissue Culture and Micropropagation
Cells differentiated
through natural life processes in several different specific ways form the
tissues and organs in organisms. The
earlier undifferentiated cells can be made to develop along specific directed
lines to develop into tissues, organs and even whole organisms in synthetic
media in the laboratory, through process a called tissue culture. While natural cells, tissues and organs can
be made to respond in tissue culture, the technique can also be used to modify
natural or tissue culture originated cells, tissues and organs in almost any
manner. On the medical side the stem cells are
being explored and exploited to develop tissues and organs for transplantation
to replace defunct parts.
The undifferentiated cells in the growing points of
plants and animals are totipotent
in the sense they can be made to develop into any type of cell of the organism
and so the whole organism, through appropriate procedures in the
laboratory. Elegant tissue culture
protocols are widely used in a variety of experimental and production phases
both for plants and animals. Since all
this happens in the laboratory glassware, it is called in vitro
(in glass), in contrast to in vivo that happens in the living systems.
In plants the growing points that contain
undifferentiated are called meristems. The meristematic
cells can be tissue cultured to produce tissues, organs and whole plants. Tissue culture produced tissues, organs and
plantlets, that constitute germplasm,
can be cryopreserved regenerated at a
later date when needed using tissue culture protocols. Pollen can be cultured to produce haploid plants (containing only one set of
chromosomes instead of the usual two sets) and even fertilization and seed
development can be achieved in vitro. This facility provides for the conservation
of plant germplasm in germplasm
banks, variously called in vitro
banks or tissue banks or gene banks.
When a piece of meristematic
plant tissue (explant)
of any part of a plant is subjected to culture protocols, it develops into an
undifferentiated mass of cells (callus), from which numerous heart shaped
structures (embryoids)
arise. Each one of these embryoids can be cultured into a whole plant in the
laboratory. The embryoids
encapsulated in calcium alginate or other suitable material, called synthetic or artificial
‘seeds’, can be cryopreserved for long
periods till required for use.
As a very large number of embryoids
develop from cultured callus, it is possible to produce thousands of
plantlets. The plantlets are transferred
to soil to acclimatize (hardened) and taken to the field to raise a crop. This process is micropropagation,
a way of cloning, which is
used extensively to produce genetically uniform plants. These plants are disease free at least till
they are taken to the soil. There are
hundreds of success stories of mass cultivation of plants produced through micropropagation with such crops as banana, plantation tree
species as eucalyptus and poplars, and ornamental species as orchids.
Cell and tissue culture techniques are also largely
required in developing whole plants from transformed cells in genetic engineering.
In vitro Banks require expensive infrastructure and expertise
in collecting, processing and culturing plant material and to preserve and
regenerate the cultured material into plants.
The viability of the banked germplasm varies
with the experimental finesse and the species, and hence it has to be
periodically checked. Germplasm banking is more reassuring than seed banks, where
once the seed viability is lost, the collections become unusable. Like the seeds in seed banks, banked in vitro
germplasm can be a source of DNA, for use in genetic
engineering even when it is unviable.
Thousands of institutions have been engaged in plant
tissue culture for over three decades and several succeeded in culturing a very
large number of economically plant species, but only a few worked on crop
plants. While many institutions claim in vitro banks, only a few such as the Plant DNA Bank in Korea, are credible. Some like the National Bureau of Plant Genetic Resources,
Material in the in
vitro banks suffers from some disadvantages. Being much more sensitive to storage
conditions, particularly temperature and humidity, than seeds and extracted
DNA, the material requires very precisely controlled facilities to ensure
longer viability periods. Though
plantlets produced through micropropagation can be
transported rather easily, other kinds of in
vitro banked material require special facilities for transit. Tissue culturing requires high level of
technical expertise and production costs are very high.
Responsibilities
of Germplasm Banks
The in vitro banks
have serious responsibilities in order to fulfill their mandates. The more important of them are:
a) Ensuring the authenticity of the scientific identity,
source and geneology of
the explant source species;
b) Adopting state of the art procedures of collection,
recording, processing, culturing and
preserving the cultured material;
c) Maintaining viability of the banked material and
replenishing material of doubtful quality;
d) Ensuring responsible use of the material supplied to
others, assuring equitable benefit sharing by all parties;
e) Networking internationally, with other in vitro banks, facilitating exchange of
knowledge and material and to prevent duplication of efforts; and
f)
Updating websites
frequently and fulfilling the promises made.
September 21, 2008
RELATED ARTICLES:
CONSERVATION OF PLANT
GENETIC RESOURCES
CONSERVATION OF PLANT
SPECIES IN SEED BANKS
CONSERVATION OF PLANT
SPECIES IN DNA BANKS