Growth, Metabolite Profile, Oxidative Status, and Phytohormone Levels in the Green Alga Acutodesmus obliquus Exposed to Exogenous Auxins and Cytokinins

The effects of auxins and cytokinins at the range of concentrations 0.0001-100 mu M on Acutodesmus obliquus (Chlorophyceae) cultures were studied. Microalga exhibited sensitivity to cytokinins in the following order: 0.01 mu M tZ>0.1 mu M Kin>1 mu M DPU, whereas the hierarchy of auxin activity was: 0.01 mu M IAA>0.1 mu M IBA>0.1 mu M PAA. Cytokinins possessed higher stimulating properties on the cell number, whereas auxins increased the size of cells. Differences in the metabolite profiles of the cultures treated with phytohormones were observed. Auxins and cytokinins had a positive effect on the photosynthetic apparatus enhancing the level of chlorophylls, carotenes, and xanthophylls. In comparison with auxins, cytokinins more effectively delayed oxidative damage by increasing the level of non-enzymatic antioxidants (ascorbate, glutathione) and the activity of enzymes scavenging reactive oxidative species (catalase, glutathione reductase, ascorbate peroxidase). On the other hand, auxins stimulated superoxide dismutase activity and provoked hydrogen peroxide generation, which may be involved in cell enlargement. All phytohormones reduced the content of abscisic acid and controlled the level of endogenous auxin and cytokinins suggesting complex interactions. Different dynamics of A. obliquus responses to auxins and cytokinins clearly demonstrated their diverse roles in algal growth and metabolism.