Exogenous auxin regulates H2O2 metabolism in roots of tomato (Lycopersicon esculentum Mill.) seedlings affecting the expression and activity of CuZn-superoxide dismutase, catalase, and peroxidase

The aim of this study was to test the effect of auxin treatment on selected parameters of the redox metabolism in roots. We found that auxin application results in a reduction in the H2O2 level in roots. The hormone stimulated CuZn-superoxide dismutase, but simultaneously increased the activities of catalase, cell wall bound ferulic acid peroxidase, and soluble peroxidase izoenzymes. The analysis of the expression of genes coding for the cytosolic izoform of CuZn-superoxide dismutase, catalase, and cell wall associated peroxidase (TPX 1) involved in cell wall stiffening and lignification revealed the stimulatory effect of exogenous auxin on the expression of the aforementioned genes. The enzyme activity and gene expression in the roots of control and auxin-treated plants were studied in daily intervals, during a 3-day-long growth cycle. The stimulatory effect of auxin on the enzymatic activity was transient with the highest stimulation observed on the second day of treatment. On the third day, the activities of the enzymes decreased. The maximal enzyme activities were preceded by a rise in gene expression. The increase in the level of CuZn-superoxide dismutase and catalase transcripts were detected after 1 day of auxin treatment. Then the expression of the aforementioned genes decreased. The period of auxin-dependent stimulation of the TPX 1 gene expression encompassed the first and the second day of treatment. Auxin stimulated CuZn-superoxide dismutase and catalase activities only in the distal zone of the root while peroxidase activity was increased by auxin in the distal as well as in the proximal parts of the organ.