T. Macek et al. Biotechnology Advances 18 2000 23–34 27
conjugated, have been identified, together with some dechlorinated products. Wilken et al. [35] studied the metabolism of 10 different congeners of PCBs in 12 cell cultures of different
plant species one culture of each species. The authors observed that metabolism of defined PCBs congeners was dependent on plant species, detecting various monohydroxylated and
dihydroxylated compounds after acid hydrolysis of polar metabolites.
Macková et al. [16,36,37] studied the ability of cultures of various species cultivated in vitro to degrade Delor 103 a mixture of PCBs commercially produced in the former Czech-
oslovakia until the mid-1980s [38,39]. The PCB mixture contained about 59 congeners with differing degrees of chlorination, with an average number of three chlorines per biphenyl
molecule. The analytical procedure was optimized by Burkhard et al. [40]. About 40 axenic cell cultures of different plant species were screened for the ability to transform PCBs. When
the PCB degradative ability in relation to the origin and morphology of the cultures was eval- uated, the results showed a great variability in the capability to convert PCBs within different
cultures of the same plant species [41,42]. The best results were obtained with
Solanum ni- grum
black nightshade hairy root clone SNC-9O. Such cultures, obtained after transforma- tion of plant cells by
Agrobacterium rhizogenes , proved to be a very useful tool in basic re-
search for phytoremediation purposes [37,43,44]. Metabolism of individual congeners of all three monochlorobiphenyls were studied and various monohydroxylated and dihydroxylated
chlorobiphenyls were detected. 4-Hydroxy derivatives were identified as the major products in all three cases of monochlorobiphenyls transformation [16].
7. Enzymes involved
In his review Cole [45] showed that oxygenation is a common process in pesticide and herbicide metabolism and it is an important initial mode of attack when organisms encounter
what are often highly lipophylic compounds. This step serves to increase water solubility and provides an opportunity for conjugation via glycosidic bond formation. In several instances
mixed function oxidases have been implicated, similar to those in mammals and insects [45]. The xenobiotics can be oxidized by cytochrome P450 and peroxidases may also be important
[46,47]. Many early examples of plant metabolic sequences of transformation, conjugation, and compartmentation three phases of xenobiotic transformation in plants reactions have
been summarized and compared with animal metabolite patterns [48]. Recent studies have shown that plants appear to contain sets of specific metabolic isoenzymes and the corre-
sponding genes. Similarities between animal and plant metabolic pathways exist; however, plant metabolism may often be more complex and an important difference from animal me-
tabolism appears to exist especially in the formation of bound residues phase III. Enzymes involved in xenobiotic metabolism were reviewed by Sandermann [48,49]. He showed that
cytochrome P450, peroxygenases, and peroxidases are involved in plant oxidations of xeno- biotics. Other enzyme classes like gluthathione S-transferases, carboxylesterases, O-gluco-
syltransferases O-malonyltransferases, N-glucosyltransferases, and N-malonyltransferases are associated with xenobiotic metabolism in plant cells, transport of intermediates, and
compartmentation processes.
Recently the question of PCB transformation and oxidative enzymes taking part in their
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
