28 T. Macek et al. Biotechnology Advances 18 2000 23–34
metabolism were studied. The effect of PCBs on the changes of the level of peroxidase activ- ity and the pattern of peroxidase isoenzymes was also followed [36,50,51]. Lee and Fletcher
[52] suggested that cytochrome P450, rather than peroxidases, is involved in the PCB degra- dation pathway. Nevertheless, we found a significant positive correlation between peroxidase
content and PCB disappearance during incubation of cultures in the presence of PCB [51].
8. Plant cells cultivated in vitro as a tool for phytoremediation experiments
Most experiments used to establish phytoremediation techniques were done with normal soil-grown or hydroponically grown plants. Recently, as more and more effort is directed to-
ward research to understand and improve the performance of plants in remediation technolo- gies, the number of results obtained with the help of in vitro plant cell and tissue cultures is
rapidly increasing. The concept is not new—in vitro cultivated plant cells have been used in studies of herbicide resistance and metabolism for many years. Other organic xenobiotics
have also been studied, as in the case of pentachlorophenol, which was shown to be metabo- lized by wheat and soybean cell suspension cultures yielding glucosides and nonextractable
residues as described by Langebartels and Harms [28]. The ability of plant cells to metabo- lize PCBs was demonstrated 10 years ago by Groeger and Fletcher [53]. Transformation of
TNT by a hairy root culture of
Catharanthus roseus was investigated by Hughes et al. [54].
They did not detect mineralization of TNT; instead, products such as 4-amino-2,6-dinitrotol- uene and 2-amino-4,6-dinitrotoluene were identified.
Following transformation of 3,4-dichloraniline by leaves and suspension cultures of soy- bean, it was observed that both systems almost completely metabolize this compound during
48 h. Mostly N-glucosyl and N-malonyl conjugates were analyzed in leaves. These conju- gates were bound to cell wall structures. Cells of suspension cultures produced soluble
N-malonylconjugates, which were excreted into the medium. It was proven that axenic cell cultures are able to metabolize certain compounds by common metabolic pathways. Plant
cell tissue culture can be a useful system with some advantages in comparison with intact plants [55]. These advantages include: 1 the material can be grown under standard labora-
tory conditions, 2 the growth is independent of the weather or climate, and 3 in vitro cul- tures often grow more rapidly. The exploitation of transformed hairy root cultures is espe-
cially rewarding, as discussed by Macková et al. [15,37], Hughes et al. [54], Macek et al. [43,56], and Betts [20]. Plant roots transformed by
Agrobacterium rhizogenes exhibit all fea-
tures of normal plant roots and grow rapidly under defined aseptic conditions in vitro [57], thus allowing the distinction to be made between the plant metabolism itself and the effect of
the complex interaction between plants and microbial communities in the rhizosphere [58]. Metabolism of many other organic compounds has been addressed with the help of plant cell
and tissue cultures, because in addition to the above advantages this model facilitates obtain- ing results with much lower analytical expenses.
9. Practical approaches
