Effect of copper and salicylic acid on phenolic metabolites and free amino acids in Scenedesmus quadricauda (Chlorophyceae)

Species of the genus Scenedesmus are frequently used in studies focused on heavy metal toxicity and phenols represent important tool for stress protection. However, deeper knowledge about accumulation of phenolic metabolites in algae still absents. We therefore studied selected metabolic responses of widely distributed green algal species Scenedesmus quadricauda to short-term (24 h) effect of copper (Cu), salicylic acid (SA) and their combined application (25 μM for both). Exposure to Cu led to decrease in chlorophylls while SA stimulated increase in chlorophylls. Soluble proteins and total soluble phenols were depressed by Cu treatment while SA had no effect and did not reverse influence of Cu in combined variant. Endogenous SA decreased in Cu + SA treatment and this depletion had no direct effect on the accumulation of the majority of detected phenolic acids, while individual amino acids seemed to be affected. Considerable accumulation of benzoic acids and their noticeable responses to SA may suggest involvement in protection against Cu toxicity since intracellular Cu remained unchanged by exposure to Cu + SA. These observations are discussed in the context of biosynthesis of phenols and possible signalling mechanisms are also suggested.