Cellular and subcellular localization of the lignin biosynthetic enzymes caffeic acid-O-methyltransferase, cinnamyl alcohol dehydrogenase and cinnamoyl-coenzyme A reductase in two monocots, sugarcane and maize

Cinnamoyl-coenzyme A reductase (CCR, EC 1.2.1.44), cinnamyl alcohol dehydrogenase (CAD, EC 1.1.1.195) and caffeic O-methyl transferase (COMT, EC 2.1.1.68) are three enzymes of the biosynthetic pathway of lignin. This pathway has been mostly studied in dicots but is less well known in monocots. We report the histochemical localization of these enzymes in maize (Zea mays L.) and sugarcane (Saccharum officinarum L.). Antibodies directed against maize COMT and sugarcane CAD and CCR were generated. Western experiments were performed with the 3 antibodies, and immunolocalization experiments were performed with anti-CAD and anti-COMT antibodies. The three enzymes were present in actively lignifying tissues, such as maize roots and mesocotyls, and sugarcane roots and stems. At the cellular level, CAD and COMT were mainly found in xylem. No major differences could be seen in the distribution patterns of both enzymes, except that CAD was detected in the endodermis, while COMT was not. At a subcellular level, the three enzymes appeared to be mainly cytosolic.