We investigated the organization of the cortical endoplasmic reticulum (ER) in prophase cells of the angiosperms Zea mays, Triticum turgidum, and Vigna sinensis. In both symmetrically and asymmetrically dividing protodermal leaf cells, cortical ER was enriched in the preprophase band and colocalized there with microtubules, forming a ring-like structure (ER ring). In contrast, ER ring was absent from prophase root-tip cells of the same plants, suggesting that ER ring formation in the preprophase band is organ specific. Immunolabeling of the protodermal leaf cells revealed the presence of acetylated microtubules, which are more stable than the nonacetylated ones. In contrast, neither this post-translational modification of tubulin nor an accumulation of ER in the preprophase band was detected in root-tip cells. Experimentally delaying the maturation/disassembly of the microtubule ring of the preprophase band by taxol or cyclopiazonic acid treatment led to the appearance of ER ring and acetylated microtubules in the preprophase band. Together, our data show that in dividing cells of angiosperms, an ER ring associated with acetylated microtubules forms in the preprophase band.