Ammonium toxicity on germination and early seedling growth of Lolium multiflorum L. (Italian ryegrass) : oxidative stress biomarkers and potential mitigation strategy based on antioxidative defence.
Thesis DisciplinePlant Biotechnology
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Ammonium (NH₄⁺) toxicity is a major issue to plant growth as well as of economic importance. Various ammonium nitrate (NH₄NO₃) concentrations were applied to Lolium multiflorum L. (Italian ryegrass) seeds to determine the threshold ammonium toxicity to this plant. It was also revealed that the toxicity of NH₄NO₃ to ryegrass seedlings, particularly root growth, was largely attributed to NH₄+ and not the nitrate ion. Histochemical detection of superoxide and hydrogen peroxide, and biochemical assays (peroxidase activity and lipid peroxidation) were also carried out to investigate the possibility that NH₄⁺ toxicity, like many other abiotic stress conditions, is linked to oxidative stress. Seeds treated with NH₄NO₃ were found to exhibit higher levels of oxidative stress (superoxide, hydrogen peroxide, peroxidase activity and lipid peroxidation). It was of interest to apply seed priming technique and antioxidant treatments to assist plants in overcoming ammonium toxicity. Casein hydrolysate as the primary seed priming agent did not assist seedlings against NH₄⁺ toxicity. It was thought that 10 and 20 mM of antioxidant treatments (L-ascorbic acid) were too probably high and inhibited germination of L. multiflorum L. seeds. Exogenous application of potassium iodide (KI) at 10 mM to Italian ryegrass seeds incubated in 1 mM ammonium sulphate [(NH₄)₂SO₄] seemed to have longer roots compared to those incubated in 1 mM (NH₄)₂SO₄ alone.