Differential superoxide dismutase expression in ryegrass cultivars in response to short term aluminium stress

Background and aims Aluminium (Al) toxicity limits pasture production in acidic soils, and there is evidence that antioxidant enzymes such as superoxide dismutase (SOD) play a key role against Al-induced oxidative stress. We have investigated (i) the relationship between Al-toxicity and oxidative damage as well as the time-course of SOD activity and (ii) the expression profiles of two SOD isoforms in the roots of two ryegrass cultivars. Methods Jumbo (Al-sensitive) and Nui (Al-semi-tolerant) ryegrass cultivars were cultured hydroponically with 0 or 0.2 mM Al. Roots were colleted during 48 h to determine Al uptake, lipid peroxidation, SOD activity and the expression of LpCu/Zn-SOD and LpFe-SOD isolated genes. Results LpCu/Zn-SOD and LpFe-SOD were classified phylogenetically as putative mitochondrial and plastidial SODs, respectively. Although Al accumulation did not differ between the two cultivars, lipid peroxidation increased 2.2-fold in Jumbo but only scarcely in Nui by the end of the time-course. An early response in terms of total SOD activity and differential expression of LpCu/Zn-SOD and LpFe-SOD genes occurred in both cultivars after Al treatment. Conclusions SOD isoforms were up-regulated over a longer period in Nui compared with Jumbo, leading finally to a greater protection in roots against the short term Al-toxicity.