Liquid Culture Systems for in vitro Plant Propagation

Nutrition of plants in greenhouses and in vitro 481
the high salt concentration increases both the multiplication rate and the total
amount of material produced (Selliah, unpublished results from Ulvik
Plantelab AS, Norway). In Begonia and Saintpaulia, the high salt
concentration increased both the multiplication rate and the total amount of
material produced.
3.2 Nutrient concentrations
The response to different concentrations of each nutrient has been studied
with many crops in soil, and later in organic substrates. Once hydroponics
was introduced for commercial production, establishing suitable
concentrations of nutrient for the crops became vital. In contrast to crops
grown in soil and organic substrates, all the nutrients must be supplied in
solution. Thus, provided that the pH is suitable, nutrient availability is no
longer a problem. However, the very availability of the nutrients means that
rapid depletion of the solution could limit growth and yield: 1) if the root
volume is too small, 2) if the rate of solution supply in an open system is
insufficient, 3) if nutrient replacement in a closed system is insufficient
(Adams, 2002). In greenhouse production one tries to obtain optimal
conditions both climatically and for nutrient uptake by the plants. Because of
environmental regulations in many countries, more and more of crop
production is in closed systems. This has forced growers to be more aware of
the proportion of the different nutrient elements in solutions. If the grower is
not fully aware, it could easily happen that one or more elements will
accumulate and become toxic, or perhaps depleted, causing deficiency.
The same situation is the case for microhydroponics systems. If one
changes the medium frequently, it is not necessary to be so accurate with the
proportion of the macro- and microelements. This is probably why MS
medium has been useful for such a range of species for so long. But if one
wants to extend the period between plantlet transfers, and leave the culture
for a longer time in the same medium, the nutrient composition has to be
fairly accurate and optimised to what the plant tissue in the culture vessels
really need.
3.3 Components of the nutrient media
Media for in vitro cultures are composed of macronutrients,
micronutrients, vitamins, amino acids and amides, sugar and sugar alcohols,
organic acids, and plant growth regulators. Buffers can also be included
(MES for pH 5.5 to 6.7 and TRIS for pH 10.0 to 11.5). These media can be
made from the basic salts, or a “ready to use pack” of most tissue culture
media can be purchased with or without added pH buffers. The most