Abstract
The effects of auxins and cytokinins at the range of concentrations 0.0001–100 µM on Acutodesmus obliquus (Chlorophyceae) cultures were studied. Microalga exhibited sensitivity to cytokinins in the following order: 0.01 µM tZ > 0.1 µM Kin > 1 µM DPU, whereas the hierarchy of auxin activity was: 0.01 µM IAA > 0.1 µM IBA > 0.1 µM 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.
Highlights
Microalgae such as Acutodesmus obliquus (Chlorophyceae) are single cell photosynthetic organisms that are known for rapid growth and high energy content
The auxin hierarchy regarding their stimulatory effects on cell number and biovolume was: 0.01 μM indole-3-acetic acid (IAA) > 0.1 μM indole-3-butyric acid (IBA) > 0.1 μM phenylacetic acid (PAA), whereas A. obliquus exhibited sensitivity to cytokinins in the following order: 0.01 μM tZ > 0.1 μM Kin > 1 μM DPU indicating that natural phytohormones are characterized by higher activity in algal cultures at the lower concentrations used in the experiments
The range of concentrations of all phytohormones demonstrated a stimulatory effect on the cell number, the degree of influence and most effective concentrations varied with the hormone type indicating that IAA and tZ are the most active at concentration of 0.01 μM; IBA, PAA, and Kin at 0.1 μM; whereas DPU at 1 μM, IAA is the most biologically active auxin, whereas tZ possesses the highest activity among cytokinins in A. obliquus cells
Summary
Microalgae such as Acutodesmus (formerly Scenedesmus) obliquus (Chlorophyceae) are single cell photosynthetic organisms that are known for rapid growth and high energy content They have a close evolutional relationship with vascular plants. There is a class of structurally unrelated synthetic phenylurea-type cytokinins (for example, N,N′-diphenylurea; DPU) with high activity in algal cultures (Piotrowska and Czerpak 2009). Natural auxins such as indole-3-acetic acid (IAA), phenylacetic acid (PAA), and indole-3-butyric acid (IBA) were identified in green algae from the Chlorella and Scenedesmus genus (Mazur et al 2001; Stirk et al 2013, 2014; Žižková et al 2017). Cytokinin-overproducing Arabidopsis thaliana had lower IAA levels (Nordström et al 2004), whereas other studies indicated that cytokinins can both
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