An Investigation into the Effects of Cadmium and Nitric Oxide on Induced Secondary Metabolism and Antioxidant System in Pimpinella anisum L. Through Transcriptional Upregulations in AIS1, PAL, SOD, R2R3-MYB, and bZIP Genes

This study was aimed to evaluate the cytoprotective role of nitric oxide (NO) against cadmium (Cd) through the potential transcriptional modifications in the expression of genes. Pimpinella anisum seedlings were treated with Cd (0 and 1 mM) and/or NO (0 and 25 μM). The Cd-associated decreases in shoot and root biomass were mitigated by the exogenously applied NO. Proline concentrations were increased in response to NO and/or Cd. Cd and NO treatments caused a considerable increase in peroxidase activities in comparison to the control. The individual Cd treatment led to the slight significant (p≤0.001) up-regulation in expression of R2R3-MYB transcription factor by 2.5 folds, while the simultaneous exposure to NO and Cd stimulated this gene by 7.2 folds (p≤0.0001). With a similar trend, NO significantly (p≤0.0001) upregulated bZIP transcription factor by 5.9 folds in Cd-treated seedlings. Likewise, upregulation (5.2 folds) in the significant (p≤0.0001) increase in expression of the phenylalanine ammonia-lyase (PAL) gene resulted from the NO+Cd application. Moreover, t-anol/isoeugenol synthase 1 (AIS1) gene was slightly stimulated (p≤0.05) in response to individual NO treatment. However, the Cd treatment resulted in a drastic significant (p≤0.0001) increase in AIS1 expression by 42 folds which was partly declined in the Cd+NO group and reached 22 folds (p≤0.0001). Moreover, the NO+Cd treatment caused significant (p≤0.0001) induction in the transcription of the superoxide dismutase (SOD) gene by 11.3 folds. The correlation observed among expression patterns of mentioned genes, therefore, highlights the close interplay between the transcription factors, secondary metabolism, and antioxidant system.