Pre-soaking in indole-3-acetic acid or spermidine enhances copper tolerance in wheat seedlings

• Indole-3-acetic acid (IAA) or spermidine (Spd) can mitigate the adverse effects of copper toxicity on wheat growth.
• Indole-3-acetic acid (IAA) or spermidine (Spd) supported the antioxidant system to attenuate copper stress.
• Indole-3-acetic acid (IAA) or spermidine (Spd) improves anatomical structure of stem in wheat plants under copper toxicity.

The effects of soaking wheat grains in 50 μM indole-3-acetic acid (IAA) or in 1000 μM spermidine (Spd) on seedling growth, drought tolerance, osmoprotectant molecule concentrations, anti-oxidant systems and stem anatomy when grown under 250 or 500 μM copper stress were investigated. The plants exposed to Cu exhibited a substantial decline in growth, relative water content (RWC), soluble proteins and total soluble sugars, activities of superoxide dismutase (SOD), guaiacol peroxidase (GPOX) and ascorbate peroxidase (APOX) and stem tissues structure. IAA or Spd alleviated the adverse effects of Cu-stress to varying degrees. Despite the preference for Spd, soaking grains in either compound increased the seedling growth, the relative water content, osmoprotectant concentrations, the activity of the anti-oxidant system and improved stem tissues structure while it reduced electrolyte leakage compared to control grains soaked in distilled water. These findings are important as the potential of IAA or Spd to alleviate the harmful effects of Cu toxicity offers an opportunity to increase the resistance of wheat plants to growth under copper stress conditions. Furthermore, the protective action of Spd was more efficient than IAA.