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Table 2.6: Example of a matrix to establish optimal auxin to cytokinin ratios and their
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concentrations, where the rows represent auxin levels and the columns represent the cytokinin
levels (Modified from Kyte and Kleyn (1996).
0
0.5
1
3
5
10
2.9.3.7 Vitamins
0 0.5 1 3 5 10
The vitamin considered most important for plant cells is thiamine (B1) (SMITH,
2000b). Other vitamins, such as nicotinic acid (B3) and pyridoxine (B6), are also
added to culture media, as they may enhance cellular response (SMITH, 2000b).
2.9.3.8 Carbohydrates
Green cells in culture are generally not photosynthetically active and require a carbon
source (SMITH, 2000b). Sucrose or glucose at 2-5% (w/v) is commonly used
(SMITH, 2000b). Higher levels of sucrose leads to low levels of photosynthesis in the
leaves (ROBERTS et al., 1990). Higher levels may however be used for embryo
culture (SMITH, 2000b). Sugars undergo caramelisation when autoclaved too long
(SMITH, 2000b). When sugars are heated they degrade and form melanoidins, which
are brown, high molecular weight compounds that can inhibit cell growth (SMITH,
2000b).
2.9.3.9 Gelling agent
The type of agar used to gel the medium can affect the response of experiments
(SMITH, 2000b). To minimise problems that arise from agar impurities, washed or
purified agar should be used (SMITH, 2000b).
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