Endoplasmic reticulum preprophase band in dividing root-tip cells of Pinus brutia

In dividing root-tip cells of Pinus brutia Ten., immunolocalization of the luminal endoplasmic reticulum (ER) proteins, which have the C-terminal HDEL sequence, reveals that the ER is reorganized during the preprophase/prophase stage. Portions of ER were arrayed into a ring-like structure at the site of the microtubule preprophase band (Mt-PPB). This preprophase ER band (ER-PPB) resembles that of the Mt-PPB. The former undergoes a maturation process closely similar to that of the latter. Our data show that the PPB region has a more complex organization than is currently believed. The probable function(s) of the ER-PPB is discussed.