Plastid microtubule-like structures in wheat are insensitive to microtubule inhibitors

The effects of microtubule inhibitors on the spectral properties of leaves of wheat (Triticum aestivum L. cv. Walde) and on the presence of plastid microtubule-like structures (MTLS) during etioplast to chloroplast transformation were examined. Amiprophos-methyl (APM, 0.1 mM), fed to leaf sections of 7-day-old dark-grown wheat, reduced the ration of phototransformable to non-phototransformable proto-chlorophyllide (PChlide), decreased the rate of the Shibata shift, and inhibited chlorophyll accumulation and grana stacking. The spectral properties of isolated etioplasts were not affected by APM. Colchicine (10 mM), fed to leaf sections, inhibited greening but had no effect on the PChlide ratio or the Shibata shift. MTLS were still visible on electron micrographs after treatment with APM or colchicine at frequencies similar to controls. A third inhibitor, vinblastine, had no effect on the spectral properties of non-irradiated or irradiated etiolated leaves except at concentrations that produced visible tissue damage before the irradiation. The effects of APM and colchicine may reflect inhibitions of respiration and protein synthesis, respectively. It is concluded that MTLS are insensitive to microtubule inhibitors and thus are probably not composed of tubulin.