Abstract
The effect of cadmium (Cd) on roots of Arabidopsis (Arabidopsis thaliana) was investigated to get further insight into the mechanisms of plant adaptation to Cd. Thirty-day-old Arabidopsis seedlings were exposed to 20 mu M CdCl2 for 0, 1, 2, 3, and 7 days. Root growth decreased by about 75% under Cd stress after 7 days of Cd exposure. Cd treatment reduced root soluble protein by 40% from the first day of exposure, and induced a 55% increase in root ammonium and a 17% increase in the contents of free amino acids, such as glutamine (Gln) and asparagine (Asn). The higher free amino acid level could be due to an increase in protease activity. Furthermore, Cd stress increased glutamate dehydrogenase (GDH) activity by 49%, whereas glutamine synthetase (GS) activity decreased. GDH activity on polyacrylamide gels showed that Cd induced both alpha- and beta-enriched isoforms. Therefore, this study showed that the ammonium assimilation process plays an important role in the response of plants to Cd stress.