Proceeding Paper Extracts of Non-Microcystin-Producing Cyanobacteria Affect the Plant Cytoskeleton and Cell Cycle † Dimitris Pappas 1, * , Ioannis-Dimosthenis S. Adamakis 2 , Spyros Gkelis 1 and Emmanuel Panteris 1, *   Citation: Pappas, D.; Adamakis, I.-D.S.; Gkelis, S.; Panteris, E. Extracts of Non-Microcystin-Producing Cyanobacteria Affect the Plant Cytoskeleton and Cell Cycle. Biol. Life Sci. Forum 2021, 4, 85. https:// doi.org/10.3390/IECPS2020-08722 Academic Editor: Yoselin Benitez-Alfonso Published: 1 December 2020 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Botany, School of Biology, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece; sgkelis@bio.auth.gr 2 Section of Botany, Department of Biology, National and Kapodistrian University of Athens, GR-15784 Athens, Greece; iadamaki@biol.uoa.gr * Correspondence: dtpappas@bio.auth.gr (D.P.); epanter@bio.auth.gr(E.P.);Tel.: +30-2310-998908 (E.P.) † Presented at the 1st International Electronic Conference on Plant Science, 1–15 December 2021; Available online: https://iecps2020.sciforum.net/. Abstract: Studies on the toxicity of cyanobacterial products on plant cytoskeleton have so far focused on the effects of microcystins (MCs), cyanobacterial toxins that inhibit protein phosphatases 1 and 2A, enzymes which are involved in plant cytoskeleton (microtubules and F-actin) organization and cell cycle progression. In this study, we investigated the effects of extracts from two non-microcystin- producing (NMP) cyanobacterial strains, Microcystis viridis TAU-MAC 1810 and Planktothrix agardhii TAU-MAC 0514, on the cytoskeleton and cell cycle of Oryza sativa (rice) root cells. Rice seedling roots were exposed for various time periods (1, 12 and 24 h) to aqueous extracts of the aforementioned strains. Treated root tips underwent either immunostaining for α-tubulin or staining of F-actin with fluorescent phalloidin, and DAPI staining of DNA. Fluorescent specimens were observed by confocal laser scanning microscopy (CLSM). Corrected total cell fluorescence (CTCF) was measured to quantify F-actin disorder. To assess cell cycle alterations, cell cycle stage frequencies were calculated. In addition, Evans Blue staining was applied to determine dead cells. Treatment with the extracts affected microtubules and F-actin, as well as the cell cycle. These findings suggest that bioactive cyanobacterial compounds, apart from MCs, can disrupt the cytoskeleton and cell cycle progression in plant cells. Keywords: cell cycle; cyanobacteria; cytoskeleton; F-actin; microtubules 1. Introduction Microcystins (MCs) are monocyclic heptapeptides, produced by several species of cyanobacteria [1]. They are potent hepatotoxins [2], but are also known to negatively affect plants [3,4]. In particular, the plant cytoskeleton (F-actin and microtubules) is an established target of MC variants [5,6], the toxicity of which lies in their ability to inhibit protein phosphatases 1 (PP1) and 2A (PP2A) [7], which participate in cytoskeleton organization [8] and cell cycle progression [9]. To date, extracts from cyanobacterial strains that produce MCs have been extensively used to study cytoskeletal and other physiological defects [3,5,10]. In this study, we investigated the effects of extracts from non-microcystin-producing (NMP) cyanobacterial strains on Oryza sativa (rice) meristematic root cells, focusing on the plant cytoskeleton and cell cycle. 2. Experiments 2.1. Culture of Cyanobacterial Strains and Biomass Extraction Two NMP cyanobacterial strains of the TAU-MAC culture collection, Microcystis viridis TAU-MAC 1810 and Planktothrix aghardii TAU-MAC 0514 [11,12], were cultured using BG- 11 medium in a 12:12 h light:dark cycle under white fluorescent lamps. Biomass was Biol. Life Sci. Forum 2021, 4, 85. https://doi.org/10.3390/IECPS2020-08722 https://www.mdpi.com/journal/blsf