Mung bean seedlings as bio-indicators for soil and water contamination by cadmium

The influence of Cd application on the growth and various biochemical processes in Mung bean (Phaseolus aureus Roxb.) seedlings was studied quantitatively. Applied cadmium reduced the growth of roots (endogenous toxic threshold value of 25 μg/g dry wt.), the growth of hypocotyls (endogenous toxic threshold value of 10 μg/g dry wt.), epicotyls (threshold value approx. 1.5 μg/g dry wt.) and leaves (endogenous toxic threshold value ± 5 μg/g dry wt.). The tissue permeability of hypocotyl segments was reduced when the endogenous Cd concentration exceeded about 25 μg/g dry wt. Cadmium reduced pigment synthesis above an endogenous concentration of 5 μg/g dry wt. and sterol synthesis in the roots above 25 μg/g dry wt. It also increased the stigmasterol-sitosterol ratio in the roots and induced a redistribution of sugars. In the roots an increase of polyunsaturated fatty acids was observed above an endogenous concentration of approximately 100 μg/g dry wt. Results on polyamine synthesis were most pronounced, the synthesis of putrescine in the roots being enhanced by about 600% at the highest Cd concentration applied (100 μM). Putrescine increased above an endogenous Cd concentration of 27 μg/g dry wt. of the roots. The most sensitive parameters to be measured in using Mung bean seedlings as bio-indicators are the growth reduction of the roots, the pigment reduction per leaf, and especially the accumulation of putrescine in the roots that occurs before any growth reduction can be seen.