Microcystin-LR induces abnormal root development by altering microtubule organization in tissue-cultured common reed (Phragmites australis) plantlets

University of Debrecen, Department of Botany, Faculty of Science and Technology, PO Box 14, H-4010 Debrecen, Hungary.
Aquatic toxicology (Amsterdam, Netherlands) (Impact Factor: 3.45). 03/2009; 92(3):122-30. DOI: 10.1016/j.aquatox.2009.02.005
Source: PubMed


Microcystin-LR (MC-LR) is a heptapeptide cyanotoxin, known to be a potent inhibitor of type 1 and 2A protein phosphatases in eukaryotes. Our aim was to investigate the effect of MC-LR on the organization of microtubules and mitotic chromatin in relation to its possible effects on cell and whole organ morphology in roots of common reed (Phragmites australis). P. australis is a widespread freshwater and brackish water aquatic macrophyte, frequently exposed to phytotoxins in eutrophic waters. Reed plantlets regenerated from embryogenic calli were treated with 0.001–40 μg ml−1 (0.001–40.2 μM) MC-LR for 2–20 days. At 0.5 μg ml−1 MC-LR and at higher cyanotoxin concentrations, the inhibition of protein phosphatase activity by MC-LR induced alterations in reed root growth and morphology, including abnormal lateral root development and the radial swelling of cells in the elongation zone of primary and lateral roots. Both short-term (2–5 days) and long-term (10–20 days) of cyanotoxin treatment induced microtubule disruption in meristems and in the elongation and differentiation zones. Microtubule disruption was accompanied by root cell shape alteration. At concentrations of 0.5–5 μg ml−1, MC-LR increased mitotic index at long-term exposure and induced the increase of the percentage of meristematic cells in prophase as well as telophase and cytokinesis of late mitosis. High cyanotoxin concentrations (10–40 μg ml−1) inhibited mitosis at as short as 2 days of exposure. The alteration of microtubule organization was observed in mitotic cells at all exposure periods studied, at cyanotoxin concentrations of 0.5–40 μg ml−1. MC-LR induced spindle anomalies at the metaphase–anaphase transition, the formation of asymmetric anaphase spindles and abnormal sister chromatid separation.

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    • "MC-RR and another unknown variant were detected in the fresh mass indicating a possible degrading metabolism of the plant toxin (Saqrane et al., 2007). Studies on the effects of MC-LR in the organization of microtubules and chromatin in root cells of P. australis demonstrated that the induction of abnormal mitotic cells coincided with concentrations where inhibition of protein phosphatases was greater than 50% (> 500 mg L –1 ) (Máthé et al., 2009). "
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    • "–1 ) (Máthé et al., 2009 "

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    • "The tips of lateral roots were fixed with 3.7% (v/v) formaldehyde and cryosectioned with a Leica Jung Histoslide 2000 microtome (Leica, Nussloch, Germany). Labeling of MTs and of chromatin was performed with the aid of a Cy3-conjugated anti-b-tubulin antibody (Sigma– Aldrich, St. Louis, Mo., USA) and DAPI, by previously described methods (Beyer et al., 2009; Máthé et al., 2009). Excitation wavelength range was 540–580 nm for Cy3 and 320–360 nm for DAPI. "
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