Cyanobacteria produce a variety of oligopeptides beyond microcystins and other metabolites. Their biological
activities are not fully recognized especially to aquatic plants. Acute toxicity tests on Spirodela polyrhiza and
Lemna minor exposed to a range of concentrations of cyanobacterial metabolites: anabaenopeptins (ANA-A, ANAB),
aeruginosins 98 (Aer-A, Aer-B), microginin-FR1 (MG-FR1), microcystin-LR (MC-LR) and cylindrospermopsin
(Cyl) were carried out to compare their influence on plant physiology. Effects of their binary mixtures were
determined by isobole approach and calculation of the combination index (CI) that indicates a type of metabolites’
interaction. Cyclic oligopeptides microcystin-LR and anabaenopeptin-A revealed the strongest inhibition
of S. polyrhiza growth while other metabolites appeared less toxic. Oxygen evolution was inhibited by Cyl, MCLR,
ANA-A, ANA-B, while both variants of aeruginosins and MG-FR1 did not affect this process. Photosynthetic
pigments’ contents decreased in S. polyrhiza exposed to ANA-A and Cyl, while MC-LR and Aer-A caused their
slight increase. 96 h-EC50 values showed that the growth of L. minor was more sensitive to MC-LR, ANA-A, MGFR1
and Cyl than the growth of S. polyrhiza. In S. polyrhiza synergistic effects of all the binary mixtures of
peptides with MC-LR on oxygen evolution were observed, while antagonistic one on the growth of S. polyrhiza
exposed to the mixtures with aeruginosins and ANA-A. The mixtures of MC-LR and MG-FR1 with cylindrospermopsin
revealed synergistic effects on the growth but antagonistic one to the O2 evolution. Quadruple
mixtures (ANA-A + MC-LR + MG-FR1+Cyl) did not reveal any inhibitive effect on the plant growth and very
slight on the oxygen evolution, irrespectively of their total concentrations. Various effects caused by ANA-A and
ANA-B suggest the importance of molecule structures of metabolites for toxicity. Composition of the mixtures of
cyanobacterial metabolites was essential for the observed effects.