The interactive effect of salinity and urea on growth, some related metabolites and antioxidant enzymes of <i>chlorella</i> sp. and <i>scenedesmus</i> sp.

Abstract

The interactive effects of Nacl and urea was investigated on growth, relative metabolites as well as antioxidant enzymes of Chlorella sp. and Scenedesmus sp. Lower salt concentration (100 mM NaCl) have no effect on dry weight and pigment content of chlorella sp. while, they decreased by increasing salt concentrations (200 and 400 mM NaCl). On the other hand carbohydrates, proteins, free amino acids and proline contents increased with elevated salt stress. Antioxidant enzymes (catalase, peroxidase, superoxide dismutase, ascorbate peroxidase and glutathione reductase) were progressively increased in chlorella sp. when exposed to various NaCl concentrations leading to an accumulation of Malondialdehyde (MDA), used as indicator of Lipid peroxidation. In case of scenedesmus (it was shown to be salt sensitive) reduction in all parameters was recorded even at lower salt concentration. Concerning the activity of antioxidant enzymes only an increase in the activity of peroxidase and Glutathione reducatase were observed, while other antioxidant enzymes decreased with salt concentration causing a remarkable increase in MDA [100% at 100 mM NaCl and 200% at higher salt concentrations (200 and 400 mM NaCl)]. With application of urea, a progressive increase in dry weight, pigment synthesis, protein, free amino acids and proline were recorded. Moreover, the addition of this nitrogen compound enhanced the activity of most antioxidant enzymes and consequently decreased the accumulation of malondialdehyde. The supplementation of urea as nitrogenous compound to the salt stressed Chlorella sp. and Scenedesmus sp. alleviate the adverse effects of salinity on both microalgae.New Egyptian Journal of Microbiology Vol. 17 (2) 2007: pp. 64-75