Storage medium, roots

It is found in many green plants as an energy storage medium, in tubers such as potatoes, in the roots of vegetables like carrots, and in the seeds of grains like rice, wheat and barley. 

Fig. 17.2. Effect of the extraction medium (A, Polyclar SB-100 B, L-cysteine+ Amberlite CG-400 and C, L-cysteine) on the storage time and/or stability of the crude extract of sweet potato root.

Storage capacity in a cell culture is available inside the cells (e.g., vacuoles) or in the extracellular compartment. The storage facilities of the latter can be remarkedly improved by the addition of liquid organic phases, resins, or other sorbents to the medium. Addition of XAD-7 to Catharanthus roseus cultures resulted in increased yields of indole alkaloids (SS). Addition of a dimethylsiloxane polymer to Eschscholtzia californica cultures improved yields of benzophenanthridine alkaloids ( 9), and increased yields of nicotine and anabasine were obtained by adding of XAD-2 and XAD-4 resins to Nicotiana transformed roots (90,91). 

In recent years a number of in vitro experiments have been reported on a variety of plant materials—segments of oat coleoptiles, segments of barley root, cut-up spinach leaves, discs of rhubarb leaves, slices of potato tubers —which demonstrate the utilization of di-and tricarboxylic acids by respiring cells and an increased rate of oxidation on addition of these substances they demonstrate further that malonate inhibits plant respiration. The stimulating effect of the substrates is often absent in fresh material, which is saturated with oxidizable substrates, but it is marked after storage, which depletes the tissue of substrates. The malonate inhibition is usually found only when the medium is acid (pH 5 or below) and when the concentration of malonate is relatively high (0.01 M and above). To obtain the same effects as in animal tissues ten- to a hundredfold concentrations of malonate are required. 

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