Cytoskeletal and developmental alterations in Ceratophyllum demersum induced by microcystin-LR, a cyanobacterial toxin

The aim of the present work was the investigation of microtubule organization related to developmental processes of Ceratophyllum demersum, a submergent aquatic macrophyte, as affected by microcystin-LR (MCY-LR), a cyanobacterial toxin. We studied the time- and dose-dependent effects of the cyanotoxin in a concentration range of 0.01-20 mu g mL(-1) (0.01-20.1 mu M) at exposure times of 2-16 d. At short term (4 d) of MCY-LR exposure we observed the inhibition of C. demersum shoot tip elongation. This phenomenon was already observed at 0.01 mu g mL(-1) MCY-LR (reduction of shoot tip length to 56 +/- 3.6% of controls) and correlated with the induction of cortical microtubule (CMT) reorientation from transverse to longitudinal known to induce radial expansion of meristematic cells instead of normal elongation. Concomitantly we detected the increase of the percentage of cells in early mitosis in shoot tip meristems. from 1.17 +/- 0.2% for controls to 1.93 +/- 0.3 at 0.01 mu g mL(-1) MCY-LR and 6.19 +/- 0.5 at 10 mu g mL(-1) MCY-LR. Cyanotoxin exposure induced the inhibition of general shoot elongation that was more pronounced than inhibition of the increase of leaf whorl number or fresh weight in the treatment period and this was observable at as short as 2-4 d of 2.5 mu g mL(-1) MCY-LR exposure. This observation further proved that the MCY-LR-induced inhibition of cell elongation is responsible mainly for growth inhibition in C. demersum. Concomitantly with developmental and growth changes MCY-LR decreased protein and chlorophyll content at 16 d of exposure: at 20 mu g mL(-1) of cyanotoxin, protein content was reduced to 53.3 +/- 2.8%, while total chlorophyll content to 46.53 +/- 2.7% of controls. This is the first study showing that MCY-LR inhibits the growth of C. demersum through cytoskeletal reorganization. This plant proved to be a powerful model system for toxicological as well as plant cell biology studies. (C) 2009 Elsevier B.V. All rights reserved.