In this article we will discuss about the Root Culture:- 1. Medium and Methods of Root Culture 2. Legumes of Root Culture 3. Nature 4. Significance.
Medium and Methods of Root Culture:
Kotte and Robbins (’22) first successfully cultured wheat root tips for a short period. In 1934 White first successfully cultured tomato roots for an unlimited period in a medium containing mineral salts, sugar and yeast extract. After this several scientists attempted to culture roots of various plants.
With roots of woody plants the success is comparatively less. But roots of some woody plants, such as, Acacia sp. and Acer rubrum L. were successfully cultured. Roots of some gymnosperms were also cultured with success.
Medium—Roots are usually grown in liquid medium. Murashige and Said (’79) observed in tomato root culture continuous and slow agitation, which helps gaseous exchange, resulted in doubling of root elongation and improved development of lateral roots. Medium supplemented with hormones helps root culture in certain cases. Inositol stimulates growth in isolated roots.
For root culture some modifications of the White’s medium is found to be beneficial. Instead of Fe (SO4)3 as the source of iron use of chelated iron, in the form of NaFeEDTA (sodium-ferric-ethyl-diamine tetracetate) is preferable, because in prolonged culture use of ferric sulphate in the medium leads to iron deficiency.
Sugar concentration of 1.5—2% is sufficient. Vitamin requirement varies according to the plant. Thiamine is needed by all species. Cereal roots require more auxin than dicot roots. A medium supplemented with sugar, IAA, sometimes cytokinin and meso-inositol helps cambial development in excised roots.
Method—Roots are grown from young seedlings produced by the germination of aseptic seeds (Fig. 7). Tomato seeds are first surface sterilized with 80% alcohol for 1 minute in 100 ml conical flask. Then the seeds are treated with chlorine water for 10 minutes. The seeds are rinsed thoroughly in double distilled water.
About 5 seeds are placed in a petridish lined with No. 1 filter paper and moistened with 8-10 c.c. of double distilled water. The petridish is wrapped with an aluminium foil and placed in an incubator at 25°C for about 5 days in dark.
Sterile root tips obtained by germination of seeds are cultured on White’s medium. About 10 mm long root tips are taken and transferred to flasks containing culture medium. The culture is incubated at 25°C for 10 days.
The root has developed and produced many lateral roots. The main root is subdivided into sectors each of which contains a portion of the main root and several lateral roots. Each such sector is placed on a fresh medium.
The lateral roots on their turn produce lateral roots. From such a culture a constant supply of root tips is available for experiments. At regular intervals subculture is done. In this way the culture can be maintained for several weeks.
Legumes of Root Culture:
A technique has been developed for culturing legume roots with Rhizobium. The basal ends of the excised roots are inserted in a small vial containing organic nutrients Apical parts of the roots are dipped in a petridish containing an inorganic medium inoculated with Rhizobium. Roots of Glycine max and Phaseolus vulgaris were grown in this way.
Nature of Root Culture:
Biochemical composition of the cultured roots may be somewhat different from the normal roots, although they may be alike in several anatomical features and metabolic pathways.
According to the response of the roots in culture the plants are of three types:
(a) Roots continue to grow indefinitely in culture producing many lateral roots, e.g., Datura, Lycopersicum.
(b) Roots after a period show decrease in growth rate and produce weak lateral roots, e.g., Pisum, Triticum, Linum etc.
(c) Lateral roots do not develop at all. This may be because the nutrient medium does not contain the substance required for the growth of the lateral roots.
Significance of Root Culture:
(1) From root culture many genetically uniform roots are produced within few days. These are called ‘clones of isolated roots’. Such uniform root tips are available for further study.
(2) From continuous culture of isolated roots the nutritional requirements of the roots can be studied. Roots of some plants require a supply of vitamin thiamine for unlimited growth. Nutritional requirements of isolated tomato roots have been noted.
(3) Root culture is also suitable for investigation on lateral root and bud formation, initiation of cambial activity and nodulation.
(4) The influence of shoot on root growth can be studied from root culture.
(5) The factors controlling the development of secondary vascular tissues can be studied from root culture. In many plants the excised roots in culture failed to develop the secondary vascular tissues. This indicates that some substances are trans located from the shoot and influence the formation and development of vascular- cambium of roots.
(6) Root culture may be used for the commercial production of useful substances.