Activity during lignin

A different approach to investigate active lignification during resistance reactions is provided by the determination of enzyme activities involved in lignin biosynthesis. Resistant plants are expected to be more strongly activated during or immediately preceding the resistance reaction compared to susceptible plants. Thus, phenylalanine ammonia-lyase (PAL) (43-45), cinnamic acid 4-hydroxylase (46), O-methyltransferases (44), and... 

Woody plants can synthesize anywhere from 15-30% of all biomass as lignin. Hence, equivalent amounts of phenylalanine are required at some point, i.e., during lignin formation, large amounts of ammonia are recycled as a consequence of PAL activity. While plants have no serious problems in obtaining glucose as a carbon source, supplied abundantly through photosynthesis,... 

Davies JL, Nakatsubo F, Murakami K, Umezawa T (1987) Organic acid pulping of wood IV Reactions of arylglycerol fi guaiacyl ethers Mokuzai Gakkaishi 33 478-486 Deobald LA, Crawford DL (1987) Activities of cellulase and other extracellular enzymes during lignin solubilization by Streptomyces vindosporus Appl Microbiol Biotechnol 26 158-163... 

Figure 11. Effect of decreasing concentrations of veratryl alcohol on veratryl alcohol oxidase activity of lignin peroxidase H8 during inhibition by hydroxylaminodinitrotoluenes (32). The reaction mixture contained in a final volume of 600 pi 0.05 pM lignin peroxidase H8, 40 mM sodium tartrate buffer pH 3.5, 260 pM H2O2, 10 pM hydroxylaminodinitrotoluenes (both isomers) and various concentrations of veratryl alcohol [mM] 11.4, A 2.8, 1.7, O 1.1, A 0.9, 0.6, control (without hydroxylaminodinitrotoluene) 1.1 mM,. ...

Curing The wood is thermally treated at a temperature ranging from 150 °C to 190°C under dry conditions, for 12-16 hours. During this stage, reactions occur between the hemicellulose breakdown products and the activated lignin to form cross-links. The wood leaves this part of the process at less than 1 % moisture content. 

The induction of PAL activity at the onset of vascular differentiation can be shown by the use of plant tissue cultures (37-39). Xylem cells with secondary and lignified walls are differentiated over a time course of 3-14 days by the application of the plant growth factors naphthylene acetic acid (NAA) and kinetin in the ratio 5 1 (1.0 mg/liter NAA, 0.2 mg/liter kinetin) to tissue cultures of bean cells (Phaseolus vulgaris) (37,40). The time for differentiation varies with the type of culture, solid or suspension, and with the frequency and duration of subculture, but for any one culture it is relatively constant (37,41,42). At the time of differentiation when the xylem vessels form, the activity of PAL rises to a maximum. The rising phase of the enzyme activity was inhibited by actinomycin D and by D-2,4-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide (MDMP) applied under carefully controlled conditions (42). This indicated that both transcription and translation were necessary for the response to the hormones. Experiments using an antibody for PAL and a cDNA probe for the PAL-mRNA have also shown that there is an increase in the amount of transcript for PAL during the formation of lignin when Zinnia mesophyll cells are induced to form xylem elements in culture (Lin and Northcote, unpublished work). 

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