TY - CHAP
T1 - Immunolocalization of enzymes involved in lignification
AU - Takabe, Keiji
AU - Takeuchi, Miyuki
AU - Sato, Takahiko
AU - Ito, Masaki
AU - Fujita, Minoru
N1 - Funding Information:
In contrast to the enzymes involved in synthesis of monolignols, POX is synthesized in the rough endoplasmic reticulum and transported to the Golgi apparatus where glycosylation of POX might occur. Thereafter, the processed POX is transported to the plasma membrane by fusion of the Golgi-vesicles to the plasma membrane. POX immunolabeling is usually observed below the membrane of the rough endoplasmic reticulum, indicating that the synthesis and processing of POX might localize to the rough endoplasmic reticulum membranes and the Golgi apparatus. Therefore, POX is separated from the monolignols synthesized in the cytosol by the membrane of the rough endoplasmic reticulum and the Golgi apparatus in the cell. When POX is transported to the plasma membrane, it locates at the outer surface of the plasma membrane. This is supported by hydropathy plot analysis of POX. Monolignols might pass through the plasma membrane via mechanisms that are still unknown, and localize at the boundary between the plasma membrane and newly formed cell wall. Then, POX exposed to the newly formed cell wall might oxidize the monolignols in the presence of hydrogen peroxide to form monolignol radicals. The radicals are then transported to the outer portion of cell wall and polymerized. shows a schematic representation of lignin biosynthesis based on our results. Figure 3
PY - 2001
Y1 - 2001
N2 - Localization of the enzymes involved in lignification is essential to better understand the dynamic aspect of lignin biosynthesis in the cell, as well as to better understand the regulation of lignification in woody plants. Lignification has three steps: 1) biosynthesis of the monolignols, 2) transport and secretion of monolignols, and 3) dehydrogenative polymerization of the monolignols. Though most of the enzymes involved in lignification have been identified, their localization in the cell and cell wall remains equivocal. To obtain more detailed information, we investigated the localization of enzymes involved in lignification within the cell and the cell wall in poplar trees using immunocytochemistry. Immunolabeling of phenylalanine ammonia-lyase, caffeate O-methyltransferase, 4-coumalate:CoA ligase, and cinnnamyl alcohol dehydrogenase was localized in the differentiating xylem. These enzymes were particularly abundant during secondary wall formation. Immunolabeling was observed on the polysomes and in the cytosol of the cells during secondary wall formation, indicating that these enzymes are synthesized in the polysomes and released in the cytosol. The synthesis of monolignols might occur in the cytosol. Immunolabeling of peroxidase was also localized in the differentiating xylem, particularly during secondary wall formation. The labeling, however, was observed in the rough-endoplasmic reticulum, the Golgi apparatus, and the plasma membrane, indicating that peroxidase is synthesized in the r-ER, transported to the Golgi apparatus, and localized at the plasma membrane by fusion of the Golgi vesicles to the membrane. The most interesting feature of the present results is that the enzymes involved in monolignol synthesis are separated from the enzyme involved in polymerization of monolignols in the cell by the membrane. Monolignols passing through the plasma membrane are polymerized dehydrogenatively in the cell wall in the presence of peroxidase and hydrogen peroxide.
AB - Localization of the enzymes involved in lignification is essential to better understand the dynamic aspect of lignin biosynthesis in the cell, as well as to better understand the regulation of lignification in woody plants. Lignification has three steps: 1) biosynthesis of the monolignols, 2) transport and secretion of monolignols, and 3) dehydrogenative polymerization of the monolignols. Though most of the enzymes involved in lignification have been identified, their localization in the cell and cell wall remains equivocal. To obtain more detailed information, we investigated the localization of enzymes involved in lignification within the cell and the cell wall in poplar trees using immunocytochemistry. Immunolabeling of phenylalanine ammonia-lyase, caffeate O-methyltransferase, 4-coumalate:CoA ligase, and cinnnamyl alcohol dehydrogenase was localized in the differentiating xylem. These enzymes were particularly abundant during secondary wall formation. Immunolabeling was observed on the polysomes and in the cytosol of the cells during secondary wall formation, indicating that these enzymes are synthesized in the polysomes and released in the cytosol. The synthesis of monolignols might occur in the cytosol. Immunolabeling of peroxidase was also localized in the differentiating xylem, particularly during secondary wall formation. The labeling, however, was observed in the rough-endoplasmic reticulum, the Golgi apparatus, and the plasma membrane, indicating that peroxidase is synthesized in the r-ER, transported to the Golgi apparatus, and localized at the plasma membrane by fusion of the Golgi vesicles to the membrane. The most interesting feature of the present results is that the enzymes involved in monolignol synthesis are separated from the enzyme involved in polymerization of monolignols in the cell by the membrane. Monolignols passing through the plasma membrane are polymerized dehydrogenatively in the cell wall in the presence of peroxidase and hydrogen peroxide.
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U2 - 10.1016/S0921-0423(01)80071-X
DO - 10.1016/S0921-0423(01)80071-X
M3 - Chapter
AN - SCOPUS:77957816365
T3 - Progress in Biotechnology
SP - 177
EP - 186
BT - Progress in Biotechnology
PB - Elsevier
ER -