As traditional breeding techniques failed to keep pace with demand and
to provide sufficiently fast and efficient systems for crop improvement,
another technology called tissue culture got developed. What does tissue
culture mean? It was learnt by scientists, during 1950s, that whole
plants could be regenerated from explants, i.e., any part of a plant taken
out and grown in a test tube, under sterile conditions in special nutrient
media. This capacity to generate a whole plant from any cell/explant is
called totipotency. You will learn how to accomplish this in higher
classes. It is important to stress here that the nutrient medium must
provide a carbon source such as sucrose and also inorganic salts,
vitamins, amino acids and growth regulators like auxins, cytokinins
etc. By application of these methods it is possible to achieve propagation
of a large number of plants in very short durations. This method of
producing thousands of plants through tissue culture is called micropropagation.
Each of these plants will be genetically identical to the
original plant from which they were grown, i.e., they are somaclones.
Many important food plants like tomato, banana, apple, etc.,
have been
produced on commercial scale using this method. Try to visit a tissue
culture laboratory with your teacher to better understand and appreciate
the process.
Another important application of the method is the recovery of
healthy plants from diseased plants. Even if the plant is infected with a
virus, the meristem (apical and axillary) is free of virus. Hence, one
can remove the meristem and grow it in vitro to obtain virus-free plants.
Scientists have succeeded in culturing meristems of banana, sugarcane,
potato, etc.
Scientists have even isolated single cells from plants and after
digesting their cell walls have been able to isolate naked protoplasts
(surrounded by plasma membranes). Isolated protoplasts from two
different varieties of plants – each having a desirable character – can be
fused to get hybrid protoplasts, which can be further grown to form a
new plant. These hybrids are called somatic hybrids while the process
is called somatic hybridisation. Imagine a situation when a protoplast
of tomato is fused with that of potato, and then they are grown – to form
new hybrid plants combining tomato and potato characteristics. Well,
this has been achieved – resulting in formation of pomato; unfortunately
this plant did not have all the desired combination of characteristics for
its commercial utilisation.
