Reaction of spruce cells toward heavy metals and the influence of culture conditions

Background. Plant cell cultures may serve as biosensors for the detection of heavy metals and other toxic substances. Standard culture media and protocols are frequently utilised, but in these media no care is usually taken to control the influence of hormones and nutrients on the reaction of the enzymes or metabolites under consideration as parts of the sensor. The present paper investigates the influence of media composition on the reaction of spruce cells towards heavy metals. Methods. Spruce cell cultures were grown in a standard medium, either i) alone, ii) containing 0.3% sucrose or iii) containing 3% sucrose and the hormones BAP and NAA. The cell cultures were then incubated in medium with fungal elicitor, H₂O₂, CdSO₄ (50 to 500 μM), or, alternatively, with a standard heavy metal mixture containing 80 μM Na₂HAsO₄, 150 μM CdSO₄ and 200 μM PbCl₂. Results. Depending on the nutrient status and hormone availability, large differences in glutathione contents and the GSH/ GSSG ratio were observed. However, the cellular redox state seemed to remain more or less constant. Glutathione S-transferase activity was determined with four substrates, and high induction rates for the conjugation of three substrates were observed when hormones were omitted from the media. 1,2-epoxy-nitrophenoxy- propane conjugation was highest in starving cells in the presence of hormones, showing a transient GST induction, with highest rates occurring after 16 hrs following incubation; the induction effect was lost after 24 hrs. Conclusion. A medium containing 3% sucrose and both hormones (BAP and NAA) appears to be most favourable for cellular growth as well as the expression of a basis level of detoxification enzymes and antioxidants. With this combination, early responses towards heavy metals at low concentration can be monitored. Recommendations and Perspective: Plant cell cultures are valuable tools for the bioindication of heavy metals and toxic xenobiotics. If standard media and protocols are utilised, the influence of hormones and nutrients on the reaction of the biosensor have to be evaluated thoroughly.