Effect of aluminium on nitrogen assimilation in roots of Lotus japonicus

Nitrogen assimilation and free amino acid levels were studied in Lotus japonicus L. roots exposed to low pH and aluminium stress. Both treatments reduced the activity of glutamine synthetase and glutamate synthase and their corresponding protein level in the root tissue determined by Western blotting. The decline in the rates of nitrogen assimilation was followed by a decrease in the levels of most amino acids including Asn, which is the most dominant amino acid in Lotus roots. On the other hand, strong increase has been observed in the level of proline that is probably not only the stress signal molecule but can also be involved in the stress defence. The results show that the impact of Al stress on nitrogen assimilation and amino acid metabolism is apparent, and also suggest a drop in N-transport via a decrease of Asn, the main transport form of nitrogen in L. japonicus.