title: Microcystin-LR, a protein phosphatase inhibitor, induces alterations in mitotic chromatin and microtubule organization leading to the formation of micronuclei in Vicia faba.
abstract: OBJECTIVE
  Microcystin-LR (MCY-LR) is a cyanobacterial toxin, a specific inhibitor of type 1 and 2A protein phosphatases (PP1 and PP2A) with significant impact on aquatic ecosystems. It has the potential to alter regulation of the plant cell cycle. The aim of this study was improved understanding of the mitotic alterations induced by cyanotoxin in Vicia faba, a model organism for plant cell biology studies.
  
  
  METHODS
  Vicia faba seedlings were treated over the long and short term with MCY-LR purified in our laboratory. Short-term treatments were performed on root meristems synchronized with hydroxylurea. Sections of lateral root tips were labelled for chromatin, phosphorylated histone H3 and β-tubulin via histochemical and immunohistochemical methods. Mitotic activity and the occurrence of mitotic alterations were detected and analysed by fluorescence microscopy. The phosphorylation state of histone H3 was studied by Western blotting.
  
  
  RESULTS
  Long-term MCY-LR exposure of lateral root tip meristems increased the percentage of either early or late mitosis in a concentration-dependent manner. We observed hypercondensed chromosomes and altered sister chromatid segregation (lagging chromosomes) leading to the formation of micronuclei, accompanied by the formation of disrupted, multipolar and monopolar spindles, disrupted phragmoplasts and the hyperphosphorylation of histone H3 at Ser10. Short-term MCY-LR treatment of synchronized cells showed that PP1 and PP2A inhibition delayed the onset of anaphase at 1 µg mL(-1) MCY-LR, accelerated cell cycle at 10 µg mL(-1) MCY-LR and induced the formation of lagging chromosomes. In this case mitotic microtubule alterations were not detected, but histone H3 was hyperphosphorylated.
  
  
  CONCLUSIONS
  MCY-LR delayed metaphase-anaphase transition. Consequently, it induced aberrant chromatid segregation and micronucleus formation that could be associated with both H3 hyperphosphorylation and altered microtubule organization. However, these two phenomena seemed to be independent. The toxin may be a useful tool in the study of plant cell cycle regulation.
authors: University of Debrecen, Department of Botany, Debrecen, Hungary.
authors: Dániel
authors: D
authors: Beyer
authors: Ildikó
authors: I
authors: Tándor
authors: Zoltán
authors: Z
authors: Kónya
authors: Róbert
authors: R
authors: Bátori
authors: Janos
authors: J
authors: Roszik
authors: György
authors: G
authors: Vereb
authors: Ferenc
authors: F
authors: Erdodi
authors: Gábor
authors: G
authors: Vasas
authors: Márta
authors: M
authors: M-Hamvas
authors: Károly
authors: K
authors: Jambrovics
authors: Csaba
authors: C
authors: Máthé
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D002843:Chromatin / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000302:isolation & purification / Q000494:pharmacology; D006657:Histones / Q000378:metabolism; D008387:Marine Toxins; D018519:Meristem / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D052998:Microcystins / Q000302:isolation & purification / Q000494:pharmacology*; D046931:Microcystis / Q000737:chemistry*; D048629:Micronuclei, Chromosome-Defective / Q000187:drug effects*; D008870:Microtubules / Q000187:drug effects* / Q000378:metabolism; D008938:Mitosis / Q000187:drug effects; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D010940:Plant Proteins / Q000037:antagonists & inhibitors; D031307:Vicia faba / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D002843:Chromatin; D004791:Enzyme Inhibitors; D006657:Histones; D008387:Marine Toxins; D052998:Microcystins; D010940:Plant Proteins; D010749:Phosphoprotein Phosphatases; C057862:cyanoginosin LR