Proline alleviates heavy metal stress in Scenedesmus armatus.

Growth and some metabolic activities of Scenedesmus armatus grown in the presence of different heavy metals (Cd, Mn and Ni) with and without exogenously added proline (Pro) were monitored. The growth of S. armatus cells (cell concentration, pigment and dry mass) was inhibited by all these heavy metals. Addition of Pro to the culture medium minimized the toxic effect of the metals. The growth rate was somewhat higher in Pro-containing cultures and started to decline 1 d later than in cultures containing heavy metals alone. S. armatus cells accumulated the added Pro in response to heavy metals. The accumulation correlated with protein content. Cd was the strongest inducer of Pro accumulation, Mn being the weakest. Cells accumulated nickel more than cadmium and manganese. Heavy metal-treated cells had increased peroxidase and catalase activities.