1752 Fig. 4 The P2 (a, c) and P3 (b, d) sub-cellular fractions of moss (a, b) and corn (c, d) were processed for transmission microscopy as described in ‘‘Materials and methods’’. The ER membrane vesicles and ribosomal dots are marked by arrows These vesicles were more prominent in the P2 fraction compared to the P3. These results suggest that the putative ABPs may be associated with membranes and/or vesicles. Immuno-precipitation using anti-KDEL monoclonal antibodies and detection using anti-ABP1 antiserum Since the classical corn ABP1 is known to possess a C- terminal KDEL sequence and to be retained in the ER, it was investigated if any of the moss polypeptides sharing the immunological epitopes of ABP1 also possesses a KDEL epitope. Monoclonal antibodies raised against the KDEL sequence were used to immuno-precipitate proteins from the P2 sub-cellular fractions as described previously. Equal amounts of protein from the immuno-precipitated samples of moss and corn were either silver stained or transferred to a polyvinylidene ﬂuoride (PVDF) membrane and probed with anti-ABP1 antiserum (Fig. 5). None of the 31–33 or 46 kDa polypeptides was detected by the monoclonal antibody, while the 22–24 kDa ABP1 of corn was clearly detected (Fig. 5). These results suggest that the identiﬁed putative moss ABPs do not include a KDEL signal peptide sequence. It indicates further that the putative ABPs of higher molecular mass identiﬁed in corn and Funaria by Western blotting do not possess the ER retention signal, thus not being a mere ﬁnding in lower plants. 123 Plant Cell Rep (2009) 28:1747–1758 Fig. 5 Protein samples from the membrane enriched fractions of moss, Funaria hygrometrica (M) and corn, Zea mays (C) were immuno-precipitated using anti-KDEL monoclonal antibodies. The polypeptides were separated on a SDS gel and either stained by silver (left side of the marker) or probed on a Western blot using anti-ABP1 antiserum as described in ‘‘Materials and methods’’