Microcystin-LR and cyanobacterial extracts alter the distribution of cell wall matrix components in rice root cells

Cyanobacterial toxins (known as cyanotoxins) disrupt the plant cytoskeleton (i.e. microtubules and F-actin), which is implicated in the regulation of cell wall architecture. Therefore, cyanotoxins are also expected to affect cell wall structure and composition. However, the effects of cyanobacterial toxicity on plant cell wall have not been yet thoroughly studied. Accordingly, the alterations of cell wall matrix after treatments with pure microcystin-LR (MC-LR), or cell extracts of one MC-producing and one non-MC-producing Microcystis strain were studied in differentiated Oryza sativa (rice) root cells. Semi-thin transverse sections of variously treated LR-White-embedded roots underwent immunostaining for various cell wall epitopes, including homogalacturonans (HGs), arabinogalactan-proteins (AGPs), and hemicelluloses. Homogalacturonan and arabinan distribution patterns were altered in the affected roots, while a pectin methylesterase (PME) activity assay revealed that PMEs were also affected. Elevated intracellular Ca2+ levels, along with increased callose and mixed linkage glucans (MLGs) deposition, were also observed after treatment. Xyloglucans appeared unaffected and lignification was not observed. The exact mechanism of cyanobacterial toxicity against the cell wall is to be further investigated.