Abstract
In 10-d-old soybean seedlings, the growth of roots and shoots was significantly inhibited at 50 and 100 mu M and more Cd2+, respectively, and by 50 CIM or more Ni2+. Although total protein content of roots exposed to 200 mu M Cd2+ or Ni2+ was similarly decreased compared to the control, the activity of nitrate reductase was much more inhibited by Cd2+. Ni2+-treatment (200 mu M) induced an accumulation of all free amino acids in roots associated with a decrease in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities reflecting the accumulation of both alanine and aspartic acid, respectively. Cd2+-treatment (200 mu M) decreased the amount of all free amino acids. In addition, cysteine which is the main amino acid consisting the phytochelatin complexes constituted about 17.5% of total free amino acids. The activities of both ALT and AST in Cd2+-treated roots were higher than in Ni2+-treated roots suggesting higher conversion of alanine and aspartate to pyruvate and oxaloacetate. Primary leaves excised from either Cd2+ or Ni2+-treated seedlings showed similar pattern of enzyme activities as roots.