CENTRIN HOMOLOGS IN HIGHER-PLANTS ARE PROMINENTLY ASSOCIATED WITH THEDEVELOPING CELL PLATE

Centrin and calmodulin are members of the EF-hand calcium-binding supe rfamily of proteins. In this study we compared localisation and immuno blotting of centrin with calmodulin in several monocot (onion and whea t) and dicot (mung bean and A. Arabidopsis) plants. We confirmed. that an anti-calmodulin antibody recognised a 17 kDa protein in all specie s tested and localises to the cytoplasm, mitotic matrix and with micro tubules of the preprophase band and phragmoplast. In contrast, immunob lotting using anti-centrin antibodies shows that plant centrins vary f rom 17 to 20 kDa. Immunofluorescence microscopy with anti-centrin anti bodies revealed only weak centrin immunoreactivity in the cytoplasm, n ucleus, nuclear envelope, phragmoplast and mitotic matrix in meristema tic cells. There was a slightly more intense perinuclear labelling in large differentiating onion cells and between separating anaphase chro mosomes. While centrin is known to localise to the mitotic spindle pol es in animal and algal cells, there was no appreciable immunoreactivit y at the spindle poles in higher plants. In contrast, there was an int ense immunofluorescence signal with anti-centrin antibodies in the dev eloping cell plate. Further characterisation of the cell plate labelli ng by immunogold electron microscopy shows centrin immunoreactivity wa s closely associated with vesicles in the cell plate. Our observations suggest that centrin may play a role in cell plate formation.