ASSOCIATION OF CAFFEOYL COENZYME-A 3-O-METHYLTRANSFERASE EXPRESSION WITH LIGNIFYING TISSUES IN SEVERAL DICOT PLANTS

Caffeoyl coenzyme A 3-O-methyltransferase (CCoAOMT) was previously sho wn to be associated with lignification in both in vitro tracheary elem ents (ifs) and organs of zinnia (Zinnia elegans). However, it is not k nown whether this is a general pattern in dicot plants. To address thi s question, polyclonal antibodies against zinnia recombinant CCoAOMT f usion protein were raised and used for immunolocalization in several d icot plants. The antibodies predominantly recognized a protein band wi th a molecular mass of 28 kD on western analysis of tissue extracts fr om zinnia, forsythia (Forsythia suspensa), tobacco (Nicotiana tabacum) , alfalfa (Medicago sativa), and soybean (Glycine max). Western analys es showed that the accumulation of CCoAOMT protein was closely correla ted with lignification in in vitro TEs of zinnia. Immunolocalization r esults showed that CCoAOMT was localized in developing TEs of young zi nnia stems and in TEs, xylem fibers, and phloem fibers of old stems. C CoAOMT was also found to be specifically associated with all lignifyin g tissues, including TEs, xylem fibers, and phloem fibers in stems of forsythia, tobacco, alfalfa, soybean, and tomato (Lycopersicon esculen tum). The presence of CCoAOMT was evident in xylem ray parenchyma cell s of forsythia, tobacco, and tomato. In forsythia and alfalfa, pith pa renchyma cells next to the vascular cylinder were lignified. According ly, marked accumulation of CCoAOMT in these cells was observed. Taken together, these results showed a close association of CCoAOMT expressi on with lignification in dicot plants. This supports the hypothesis th at the CCoAOMT-mediated methylation branch is a general one in lignin biosynthesis during normal growth and development in dicot plants.