Abstract
Aquatic organisms are exposed to many stressors, e.g., heavy metals. Brassinosteroids, a plant hormone group, can effectively stimulate plants to defend against the negative impact of a heavy metal. The present study was conducted with an aim to find out the influence of 24-epibrassinolide (EBL) on Acutodesmus obliquus treated with 0.01 and 500 μM of lead (Pb) ions during 7 days of cultivation. Pb has a toxic effect on algal cultures because it limits both the growth and development and induces oxidative stress. Simultaneously, 1 μM EBL was involved in protecting algal cells against the toxic effect of Pb. Despite the presence of Pb, EBL significantly increased the number of algal cells and their metabolite content (e.g., proteins, monosaccharides, chlorophylls, carotenes, and xanthophylls). Cultures treated concurrently with EBL and Pb were characterized by a reduction in their content of endogenous Pb, H2O2, and malondialdehyde. Also, EBL increased the activity of catalase, ascorbate peroxidase, superoxide dismutase, glutathione reductase, and the content of ascorbate and glutathione. EBL increased the phytochelatin synthase activity, thereby enhancing the production of phytochelatins accountable for both binding and detoxification of Pb. These results indicate the influence of EBL on the inhibitory effect of Pb in A. obliquus. These findings help to clarify the role of BRs in the algal adaptation to the prevailing stressful conditions.
Highlights
Various environmental factors influence the life in ecosystems, and many factors affect the modification of morphological and physiological processes in plant organisms
The inhibition of growth and a reduction in the content of all the above parameters was detected in A. obliquus cultures exposed to 500 μM Pb
The growth and level of studied A. obliquus metabolites increased together with the increase in the exposure time to EBL and/or Pb reaching the maximum on the 5th day of cultivation, except for 500 μM Pb and 500 μM Pb mixed with 1 μM EBL
Summary
Various environmental factors influence the life in ecosystems, and many factors affect the modification of morphological and physiological processes in plant organisms. Increased content of toxic metals in the aquatic environment affects all organisms; the most endangered are algae, which are the main producers of aquatic ecosystems and are a valuable part of the food chain (Zhou et al 2011; Rajamani et al 2014). The green alga Acutodesmus obliquus is a good model for studying the direct action of exogenous growth substances, as the reception of the hormonal, environmental stimulus and the biochemical response is not dispersed and occurs within a single cell (Bajguz and Asami 2004). Metal ions bond strongly with ligands to form the structure of the cell
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