Tungsten affects the cortical microtubules of Pisum sativum root cells: experiments on tungsten–molybdenum antagonism

Tungsten (W) is increasingly shown to be toxic to various organisms, including plants. Apart from inactivation of molybdo‐enzymes, other potential targets of W toxicity in plants, especially at the cellular level, have not yet been revealed. In the present study, the effect of W on the cortical microtubule array of interphase root tip cells was investigated, in combination with the possible antagonism of W for the pathway of molybdenum (Mo). Pisum sativum seedlings were treated with W, Mo or a combination of the two, and cortical microtubules were examined using tubulin immunofluorescnce and TEM. Treatments with anti‐microtubule (oryzalin, colchicine and taxol) or anti‐actomyosin (cytochalasin D, BDM or ML‐7) drugs and W were also performed. W‐affected cortical microtubules were low in number, short, not uniformly arranged and were resistant to anti‐microtubule drugs. Cells pre‐treated with oryzalin or colchicine and then treated with W displayed W‐affected microtubules, while cortical microtubules pre‐stabilized with taxol were resistant to W. Treatment with Mo and anti‐actomyosin drugs prevented W from affecting cortical microtubules. Cortical microtubule recovery after W treatment was faster in Mo solution than in water. The results indicate that cortical microtubules of plant cells are indirectly affected by W, most probably through a mechanism depending on the in vivo antagonism of W for the Mo‐binding site of Cnx1 protein.