Interaction of triacontanol and arsenic on the ascorbate-glutathione cycle and their effects on the ultrastructure in Coriandrum sativum L.

Exogenous application of triacontanol (TRIA) has the ability to mitigate the adverse effects of abiotic stresses by modulating a number of physio-biochemical processes in different plants. However, information about how its effects may be mediated under heavy metal stress is scanty. In this study, we evaluated how TRIA exerted its role against the toxicity of sodium arsenate in coriander (Coriandrwn sattnan L.). The activities of enzymes, including ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione-S-transferase (GST), were measured. In addition, the contents of ascorbate (ASC), dehydroascorbate (DHA), reduced glutathione (GSH) and some elements including both As and the nutrients Ca, Mg, Zn, K, P were determined. Results suggested that As decreased GSH, ASA and DHA contents, a clear indication of oxidative stress, but their amounts were raised by TRIA treatment. Also, As stress decreased plant Ca, Zn, K, Mg and P contents, while TRIA improved their uptake and inhibited As accumulation. As 200 mu M treatment inhibited the activities of APX, MDHAR, DHAR, and GR, enzymes of the ascorbate-glutathione cycle (AGC). TRIA supplementation restored and even enhanced the activity of all the AGC enzymes. 10 mu M TRIA treatment increased GST gene expression and activity to a greater extent than under only As treatment. TRIA-alone treatments did not change the mentioned parameters. Transmission electron microscopy (TEM) observations showed that TRIA was able to protect cells, and most of all chloroplasts, from As-induced damage. These results clearly indicate the protective role of TRIA in modulating the redox status of the plant system through the antioxidant AGC and GSH enzymes, which could counteract arsenic-induced oxidative stress.