Response of cadmium enrichment and free amino acids content in seedlings of two castor varieties to cadmium stress

As important primary nitrogen metabolites in plant tissue, free amino acids have been widely used to understand the nitrogen metabolism mechanism of plants under different environmental stress. To reveal the changes of cadmium (Cd) absorption and free amino acids in castor under the stress of Cd, a hydroponic experiment was performed to study the effect of Cd stress (0, 1, 2, and 5mg·L−1) on the biomass and free amino acids secretion of two castor varieties seedlings (Zibo-3 and Zibo-9). The results indicated that the biomasses of the two castor varieties under 1 and 2mg·L−1 Cd addition were not decreased significantly (p<0.05) compared with the control, while 5mg·L−1 of Cd treatment reduced the biomass of Zibo-3 and Zibo-9 by 23.3% and 11.8%, respectively. Additionally, when spiked with higher Cd dose addition, the bioaccumulation factors for Cd in Zibo-9 were higher than those in Zibo-3, thus Zibo-9 showed higher tolerance and absorption ability to Cd. The comparison between both studied castor varieties indicated that Cd stress resulted in a differential but coordinated response of amino acid levels, which are playing a significant role in plant adaptation to Cd stress.