Changes in growth, ammonium assimilation and amino acid levels in leaves of Arabidopsis thaliana under cadmium treatment

Abstract

Cadmium is the most harmful soil pollutant due to its long biological half-life. In the present study, the effect of Cd on ammonium assimilation in Arabidopsis thaliana wild-type Col0 was investigated. Thirty-day-old Arabidopsis seedlings were exposed to 20 µM CdCl2 during different exposure times (0, 1, 2, 3, and 7 days). Seedling growth decreased under Cd stress mainly after 7 days of Cd exposure. Cd stress caused a gradual decrease in soluble leaf protein and induced an increase in leaf ammonium and the content of free amino acids such as glutamine (Gln), glutamate (Glu), asparagine (Asn), and proline (Pro), which may be related to the increase in protease activity. The results showed that the activities of Glutamine Synthetase (GS) and glutamate dehydrogenase (GDH) were inversely related. Cd stress led to an increase in GDH activity, whereas GS activity decreased. GDH activity on polyacrylamide gels showed that Cd induced both β- and α-enriched isoforms. Therefore, this study confirms that the ammonium assimilation process plays an important role for plants in adapting to Cd stress.