The objective of the present study was to investigate the correlation of soluble apoplastic peroxidase activity with lignification in needles of field-grown Norway spruce (Picea abies 1.) trees. Apoplastic peroxidases (EC 1.1 1.1.7) were obtained by vacuum infiltration of needles. The lignin content of isolated cell walls was determined by the acetyl bromide method. Accumulation of lignin and seasonal variations of apoplastic peroxidase adivities were studied in the first year of needle development. The major phase of lignification started after bud break and was terminated about 4 weeks later. This phase correlated with a transient increase in apoplastic guaiacol and coniferyl alcohol peroxidase activity. NADH oxidase activity, which is thought to sustain peroxidase activity by production of HzOz, peaked sharply after bud break and decreased during the lignification period. Histochemical localization of peroxidase with guaiacol indicated that high adivities were present in lignifying cell walls. In mature needles, lignin was localized in walls of most needle tissues including mesophyll cells, and corresponded to 80 to 130 Nmol lignin monomers/g needle dry weight. lsoelectric focusing of apoplastic washing fluids and activity staining with guaiacol showed the presence of strongly alkaline peroxidases (isoelectric point z 9) in all developmental stages investigated. New isozymes with isoelectric points of 7.1 and 8.1 appeared during the major phase of lignification. These isozymes disappeared after lignification was terminated. A strong increase in peroxidase activity in autumn was associated with the appearance of acidic peroxidases (isoelectric point 5 3). These results suggest that soluble alkaline apoplastic peroxidases participate in lignin formation. Soluble acidic apoplastic peroxidases were apparently unrelated to developmentally regulated lignification in spruce needles.

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Peroxidase (EC 1.11.1.7) and laccase (EC 1.10.3.1) activities were determined in mycorrhizal and non-mycorrhizal main and lateral roots of Picea abies (L.) Karst. (Norway spruce) and Larix decidua Mill, (larch) and in mycelia of the ectomycorrhizal fungus Laccaria amethystea (Bull.) Murr. grown under axenic conditions. Peroxidase isozyme patterns were identified after isoelectric focussing. In both tree species, mycorrhizae contained the lowest, and laterals of noninoculated plants the highest, peroxidase activities. Pure mycelia of Laccaria amethystea contained considerable laccase activity but no peroxidase activity. Laccase activity was barely detected in noninoculated laterals of spruce, but was present in noninoculated laterals of larch and in main roots of Norway spruce and larch. Highest laccase activities were found in mycorrhizae of both tree species, indicating that most of the activity was derived from the fungus. Laterals of Norway spruce contained eight, and those of larch five, acidic peroxidase isozymes. In mycorrhizae of Norway spruce and larch, specific peroxidase isozymes with pI values of 4.5 and 6.2 and 5.8 and 6.0, respectively, were almost completely suppressed. The specific suppression of peroxidase suggests that the fungal symbiont is able to modify the host defence response in mature mycorrhizae. Key words: defence mechanism, laccase, mycorrhiza, peroxidase (isozymes), plant–fungus interaction.

summary The effect of magnesium deficiency and variations of the ammonium to nitrate ratio on chlorophyll, soluble protein and antioxidative systems was investigated in current year's needles of clonal spruce trees [Picea abies (L.) Karst.]. The trees were grown for 1 yr in sand culture with circulating nutrient solutions containing sufficient (0.2 mM) or limiting (0.041 mM) concentrations of Mg. The nitrogen concentration of the nutrient solutions was not varied (5 mM) but the NO3−/NH4+‐ratio was adjusted TO 0.76 in Mg‐sufficient and to 1.86, 0.76 and 0.035 in Mg‐limited plants, Under Mg‐limitation, the chlorophyll, soluble protein and Mg‐contem were lowest in needles of trees supplied with NH4+ and highest in trees supplied with NO4− as major N‐source. Apoplastic peroxidase activities were not affected by changes in nutrition. In total needle extracts, NADH oxidase, ascorbate peroxidase, mimodehydroascorbate reductase, glutatkione reductase and asoorbate content were not, or only little, affected by changes in nutrition, except for trees grown with the highest N4+‐concentrations. Glutathtone content and guaiacol peroxidase were increased in Mg‐deficient needles. Superoxide dismutase activity was decreased in Mg‐limited needles of trees grown with N4+ and increased in needles of trees grown with NO3− as a major N‐source, Except for superoxide dismutase, the activities of antioxidant enzymes and substrates were not correlated with the decree of needle chlorosis. Superoxide dismurase activity was low compared to enzymatic activities involved in H2O2 detoxification. Supposing that the needles suffered from enhanced oxidative stress, these results suggest that scavenging of O2− was a limiting factor in stress compensation rather than the detoxification of H2O2.

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