A pot experiment was performed to assess the useful effects of seed soaking or seedling foliar spray using 0.25 mM spermine (Spm), 0.50 mM spermidine (Spd), or 1 mM putrescine (Put) on heavy metal tolerance in wheat plants irrigated with water contaminated by cadmium (2 mM Cd2+ in CdCl2) or lead (2 mM Pb2+ in PbCl2). Cd2+ or Pb2+ presence in the growth medium resulted in significant reductions in growth and yield characteristics and activities of leaf peroxidase (POD), glutathione reductase (GR), ascorbic acid oxidase (AAO), and polyphenol oxidase (PPO) of wheat plants. In contrast, significant increases were observed for Cd2+ content in roots, leaves and grains, superoxide dismutase (SOD) and catalase (CAT) activities, radical scavenging activity (DPPH), reducing power capacity, and fragmentation in DNA in comparison to controls (without Cd2+ or Pb2+ addition). However, treating the Cd2+- or Pb2+-stressed wheat plants with Spm, Spd, or Put, either by seed soaking or foliar spray, significantly improved growth and yield characteristics and activities of POD, GR, AAO, PPO, SOD, and CAT, DPPH, and reducing power capacity in wheat plants. In contrast, Cd2+ levels in roots, leaves, and yielded grains, and fragmentation in DNA were significantly reduced compared with the stressed (with Cd2+ or Pb2+) controls. Generally, seed soaking treatments were more effective than foliar spray treatments. More specifically, seed priming in Put was the best treatment under heavy metal stress. Results of this study recommend using polyamines, especially Put, as seed soaking to relieve the adverse effects of heavy metals in wheat plants.
Keywords: Antioxidant activity; Antioxidant enzymes; Cadmium; Genomic DNA; Growth and productivity; Lead; Polyamines; Wheat.