Two anti-microtubular drugs for two differential responses : a rice cell line resistant to EPC remains susceptible to oryzalin

Sensitivity to the two anti-microtubular drugs oryzalin and EPC (ethyl-N-phenylcarbamate) is shown to be uncoupled in the rice EPC-resistant ER31d cell line, derived from the corresponding ER31 mutant. The ER31d cell line grows in the presence of EPC but it remains susceptible to oryzalin. In the presence of concentrations of EPC up to 0.4 mM, ER31d cells remain viable maintaining cell anisotropy and detectable cortical microtubule array. The amount of alpha- and beta-tubulin is also maintained high through a regulatory mechanism that operates at post-transcriptional level. In contrast, all these cellular and molecular parameters are heavily affected by the addition of 1 mM oryzalin. Also, the pattern of posttranslationally modified alpha-tubulins changes in the ER31d cells compared to that of their Nihon-Masari wild type line of reference. The different response elicited by the two herbicides is discussed in relation to a possible differential sensitivity of the cortical MT array, that may in turn relate to their different tubulin-binding specificities and chemical structure.