Characterization of cell walls in bean (Phaseolus vulgaris L.) callus cultures tolerant to dichlobenil

The increase in dry weight during the culture of bean callus cultures was i nhibited by the herbicide dichlobenil (2,6-dicholorobenzonitrile) with an I -50 of 0.5 muM. However bean calli became tolerant to a concentration of 12 muM by a stepwise increase in the concentration of the inhibitor in each s ubculture. Tolerant calli growing in 2,6-dicholorobenzonitrile developed wi th hollow protuberances. Groups of cells in these protuberances had irregul ar cell walls surrounded by a thicker cell wall with a lamellate structure and without a differentiated middle lamella. FTIR spectra of tolerant cell walls revealed an increase in both esterified and non-esterified pectins. C ell wall fractionation showed that in tolerant cell walls the xyloglucan-ce llulose network of non-tolerant cell walls was partly replaced by a pectin- rich network mainly formed of cross-linked polyuronides with a large propor tion of homogalacturonan. These modifications are comparable to those descr ibed for bean calli tolerant to isoxaben, pointing to a related mechanism o f tolerance for both herbicides. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.