Immunological characterization of lamins in the nuclear matrix of onion cells

We have used polyclonal and monoclonal antibodies against different lamins from vertebrates, and the IFA antibody recognizing all kinds of intermediate filament proteins, to investigate the lamins of the nuclear matrix of Allium cepa meristematic root cells. All the antibodies react in the onion nuclear matrix with bands in the range of 60-65 kDa, which are enriched in the nuclear matrix after urea extraction, and do not crossreact with other antibodies recognizing intermediate filaments in plants (AFB, anti-vimentin and MAC 322), ruling out crossreaction with contaminating intermediate filaments of cytoplasmic bundles. In 2-D blots the chicken anti-lamin serum reacts with one spot at 65 kDa and pI 6.8 and the anti B-type lamin antibodies with another one at 64 kDa and pI 5.75. Both crossreact with IFA. The lamin is localized at the nuclear periphery and the lamina by indirect immunofluorescence. Immunogold labelling of nuclear matrix sections reveals that the protein is not only associated with the lamina, but also with the internal matrix. Taken together these results reveal that higher plants, which do not possess an organized network of cytoplasmic intermediate filaments, nevertheless present a well-organized lamina containing lamins in which at least one of them is immunologically related to vertebrate lamin B. Our data confirm that lamins are very old members of the intermediate filament proteins that have been better conserved in plants during evolution than their cytoplasmic counterparts.