Aluminium toxicity and phosphate deficiency activates antioxidant systems and up-regulates expression of phosphate transporters gene in ryegrass (Lolium perenne L.) plants.

Soil acidity, associated with aluminium (Al) toxicity and low phosphorus (P) availability, is considered the most important problem for agricultural production. Even though the Al-P interaction has been widely investigated, the impact of P-nutrition on Al-toxicity still remains controversial and poorly understood. To elucidate further insights into the underlying mechanisms of this interaction in ryegrass (Lolium perenne L.), P uptake, antioxidant responses and the gene expression of phosphate transporters were determined. Two ryegrass cultivars with different Al resistances, the Al-tolerant Nui cultivar and the Al-sensitive Expo cultivar were hydroponically grown under low (16 µM) and optimal (100 µM) P doses for 16 days. After P treatments, plants were exposed to Al doses (0 and 200 µM) under acidic conditions (pH 4.8) for 24 h. Al and P accumulation were higher in the roots of Nui than that of Expo. Moreover, lower Al accumulation was found in shoots of Nui independent of P supplies. Oxidative stress induced by Al-toxicity and P-deficiency was more severe in the Al-sensitive Expo. Expression levels of L. perenne phosphate transporters were higher in Nui than they were in Expo. While LpPHT1 expression was up-regulated by P deficiency and Al toxicity in both cultivars, LpPHT4 expression only increased in the Al-tolerant cultivar. This report shows that the higher Al-tolerance of Nui can be attributed to a greater antioxidant system under both P conditions. The observation of higher P and Al accumulation in roots of Nui might indicate that the Al-tolerance of Nui is a consequence of Al immobilization by P mediated by the high expression of phosphate transporters.