Effect of zirconium on roots of wheat (Triticum aestivum) seedlings

Microelement zirconium (Zr) is considered as an element with hardly known physiological effects. Our objective was to clarify the effect of Zr on wheat seedlings. Zr ascorbate (Zr-ASC) complex was applied as the microelement source. Two types of experiments were performed: short term effect of Zr (8-day-old seedlings were exposed to 24-hour-long Zr treatment), and long term effect of Zr when seedlings were grown in Knopp solution supplemented with different concentrations of Zr-ASC for nine days. Growth, Zr accumulation as well as the activities of the enzymes guaiacol peroxidase (POD), ascorbic acid peroxidase (APX) and glutathione reductase (GR) in roots were determined. Root growth of Zr-treated wheat seedlings was not altered by 24 h treatment. On the other hand, the 9-day-long exposure to lower Zr concentrations stimulated root growth while higher concentrations (10-50 ug/mL) caused significant inhibition of root growth. Zr accumulation was proportional with Zr concentration in the medium, with maximum value of 1.32 mg/g dry weight in roots treated with 50 ug/mL of Zr for 9 days. A slight increase of POD activity was revealed in roots exposed to lower Zr concentration (10 ug/mL) while 50 ug/mL Zr doubled the activity of peroxidase. Activities of APX and GR were influenced by Zr in similar manner as POD. Our results revealed that restricted growth, immense intracellular accumulation of Zr as well as the induced enzymatic responses occur only at extremely high Zr concentration, which is much higher than in extremely polluted areas.