Nitsch and Nitsch (1969) developed an another culture. Knudson’s medium (Knudson
1946) was developed for orchid tissue culture and is also used for fern tissue culture.
With so many choices in media formulations, one might wonder about how to choose a
medium to culture the species of interest. The choice of medium is typically determined
empirically for optimal response of the plant species; explants used for culture and plant
taxonomy are good starting points. For example, nearly all tissue cultures of plants in the
Solanaceae (the nightshade family) use MS media. Recall that MS media was developed
using tobacco, a member of this plant family. Many times a mix-and-match scheme of
macro- and micronutrients from one medium and vitamins from another has also been
successful. The composition of nutrients varies from medium to medium. For example,
MS medium has higher macronutrients than does WPM, which is suitable for most plant
species, but woody plants respond better in WPM than MS medium. It is important to
select the right medium for culture according to how the plant empirically responds in
tissue culture.
5.3.2 Growth Regulators
The basal medium (e.g., MS) is designed to keep plant tissues alive and thriving. Plant
growth regulators or hormones are needed to manipulate the developmental program of
tissues—say, to make callus tissue proliferate, or produce roots from shoots. Growth regu-
lators are the items most often manipulated as experimental factors to enhance tissue culture
conditions. The most important growth regulators for tissue culture are auxins, cytokinins,
and gibberellins. Both natural and synthetic auxins and cytokinins are used in tissue culture.
Auxins promote cell growth and root growth. The most commonly used auxins are IAA
Figure 5.1.Tissue cultures in liquid (a) and solid (b) culture media. See filter paper bridge in liquid
medium.
116 TISSUE CULTURE: THE MANIPULATION OF PLANT DEVELOPMENT