Nitrogen Uptake and Free Amino-acid Accumulation in Roots of Lotus corniculatus Cultivars under Al-stress

Nitrogen uptake and free amino acid accumulation was evaluated in two South American cultivars of Lotus corniculatus L. differing in their tolerance to Al stress. The uptake of nitrate was affected by 1 mM Al more in the sensitive cultivar INIA Draco than in a relatively tolerant UFRGS (the uptake rate was 39.1% and 52.9%, respectively, of the control value at pH=5.5), whereas the opposite was true for the uptake of ammonia (60.1% and 50.1%). Treatment with Al also decreased the free amino-acid level to similar extent in both cultivars, mostly due to the significantly decreased level of asparagine (p = 0.003 and 0.026, respectively), the dominant amino-acid in Lotus roots. On the other hand, accumulation of stress metabolite - proline was achieved that was up to 5 time higher than in control. No considerable differences in this accumulation in INIA Draco and in UFRGS were found, so it is rather unlikely that proline content could contribute to the differences in Al-tolerance between the cultivars.