The herbicide sindone B disrupts spindle microtubule organizing centers

Sindone B is classified as a “mitotic disrupter herbicide”, but little information is published on the physiological effects of this structurally unique compound. Onion root tips treated with various concentrations of sindone B were examined by light microscopy following Feulgen staining, immunofluorescence of tubulin, and electron microscopy. Numerous multipolar mitotic figures are noted in Feulgen-stained specimens. Spindle microtubule arrays are focused toward many poles instead of the bipolar arrangement of the spindle in control roots. Cortical and preprophase microtubule arrays appear unaffected. Phragmoplast arrays are also multiple and are curved and branched around the multiple nuclei that result from the multipolar spindle arrays. The cell plates established by these abnormal phragmoplast microtubule arrays are branched and reticulate. These observations indicate that sindone B interacts with the spindle microtubule organizing center so that multipolar divisions result. Phragmoplast disruption may be a secondary consequence of the multipolar division. These symptoms are also characteristic of the structurally unrelated carbamate herbicides.