Effects of the potential allelochemical α-asarone on growth, physiology and ultrastructure of two unicellular green algae

The effects of the natural phenylpropanoid α-asarone on growth pattern, photosynthesis, respiration and cell structure of two microalgae have been investigated. In cultures ofAnkistrodesmus braunii α-asarone decreases in the medium and induces a lag in growth. Both phenomena were dependent on the number of cells inoculated. By contrast, in cultures ofSelenastrum capricornutum a constant decrease of the growth rate at all inocula was observed and only a slight decrease of α-asarone in the medium occurred. In both algae α-asarone caused an initial inhibition of photosynthesis, followed by a resumption of control values. The respiratory rate ofA. braunii was not significantly affected by α-asarone, whereas inS. capricornutum respiration lowered to 60% of the control in the first 48 h and subsequently rose to values exceeding the controls by 20%. Ultrastructural observations carried out 24 and 72 h after the addition of α-asarone showed modifications of cell wall inA. braunii, an increase in the number of mithocondrial profiles per cell section inS. capricornutum, and an accumulation of electron-dense deposits in the vacuoles of both algae.