Secondarily thickened cell walls of water-conducting vessels and tracheids and support-giving sclerenchyma cells contain lignin that makes the cell walls water impermeable and strong. To what extent laccases and perox...Secondarily thickened cell walls of water-conducting vessels and tracheids and support-giving sclerenchyma cells contain lignin that makes the cell walls water impermeable and strong. To what extent laccases and peroxidases contribute to lignin biosynthesis in muro is under active evaluation. We performed an in silico study of Norway spruce （Picea abies （L.） Karst.） laccases utilizing available genomic data. As many as 292 laccase encoding sequences （genes, gene fragments, and pseudogenes） were detected in the spruce genome. Out of the 112 genes annotated as laccases, 79 are expressed at some level. We isolated five fun-length laccase cDNAs from developing xylem and an extracellular lignin-forming cell culture of spruce. In addition, we purified and biochemically characterized one culture medium laccase from the lignin-forming cell culture. This laccase has an acidic pH optimum （pH 3.8-4.2） for coniferyl alcohol oxidation. It has a high affinity to coniferyl alcohol with an apparent Km value of 3.5μM; however, the laccase has a lower catalytic efficiency （Vmax/Km） for coniferyl alcohol oxidation compared with some purified culture medium peroxidases. The properties are discussed in the context of the information already known about laccases/coniferyl alcohol oxidases of coniferous plants.展开更多
Lignin, a phenolic polymer abundant in cell walls of certain cell types, has given challenges to scientists studying its structure or biosynthesis. In plants lignified tissues are distributed between other, non-lignif...Lignin, a phenolic polymer abundant in cell walls of certain cell types, has given challenges to scientists studying its structure or biosynthesis. In plants lignified tissues are distributed between other, non-lignified tissues, Characterization of native lignin in the cell wall has been difficult due to the highly cross-linked nature of the wall components. Model systems, like plant tissue cultures with tracheary element differentiation or extracellular lignin formation, have provided useful information related to lignin structure and several aspects of lignin formation. For example, many enzyme activities in the phenylpropanoid pathway have been first identified in tissue cultures. This review focuses on studies where the use of plant tissue cultures has been advantageous in structural and biosynthesis studies of lignin, and discusses the validity of tissue cultures as models for lignin biosynthesis.展开更多
基金supported by University of Helsinki Research Funds (to A.K.)Academy of Finland (grant 251390 to A.K.)Societas pro Fauna et Flora Fennica (to H.A.M.)
文摘Secondarily thickened cell walls of water-conducting vessels and tracheids and support-giving sclerenchyma cells contain lignin that makes the cell walls water impermeable and strong. To what extent laccases and peroxidases contribute to lignin biosynthesis in muro is under active evaluation. We performed an in silico study of Norway spruce （Picea abies （L.） Karst.） laccases utilizing available genomic data. As many as 292 laccase encoding sequences （genes, gene fragments, and pseudogenes） were detected in the spruce genome. Out of the 112 genes annotated as laccases, 79 are expressed at some level. We isolated five fun-length laccase cDNAs from developing xylem and an extracellular lignin-forming cell culture of spruce. In addition, we purified and biochemically characterized one culture medium laccase from the lignin-forming cell culture. This laccase has an acidic pH optimum （pH 3.8-4.2） for coniferyl alcohol oxidation. It has a high affinity to coniferyl alcohol with an apparent Km value of 3.5μM; however, the laccase has a lower catalytic efficiency （Vmax/Km） for coniferyl alcohol oxidation compared with some purified culture medium peroxidases. The properties are discussed in the context of the information already known about laccases/coniferyl alcohol oxidases of coniferous plants.
文摘Lignin, a phenolic polymer abundant in cell walls of certain cell types, has given challenges to scientists studying its structure or biosynthesis. In plants lignified tissues are distributed between other, non-lignified tissues, Characterization of native lignin in the cell wall has been difficult due to the highly cross-linked nature of the wall components. Model systems, like plant tissue cultures with tracheary element differentiation or extracellular lignin formation, have provided useful information related to lignin structure and several aspects of lignin formation. For example, many enzyme activities in the phenylpropanoid pathway have been first identified in tissue cultures. This review focuses on studies where the use of plant tissue cultures has been advantageous in structural and biosynthesis studies of lignin, and discusses the validity of tissue cultures as models for lignin biosynthesis.
