APOPLASTIC PEROXIDASES AND LIGNIFICATION IN NEEDLES OF NORWAY SPRUCE (PICEA-ABIES L)

The objective of the present study was to investigate the correlation of soluble apoplastic peroxidase activity with lignification in needle s of field-grown Norway spruce (Picea abies L.) trees. Apoplastic pero xidases (EC 1.11.1.7)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 apo plastic peroxidase activities 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 peroxi dase activity. NADH oxidase activity, which is thought to sustain pero xidase activity by production of H2O2, peaked sharply after bud break and decreased during the lignification period. Histochemical localizat ion of peroxidase with guaiacol indicated that high activities were pr esent in lignifying cell walls. In mature needles, lignin was localize d in walls of most needle tissues including mesophyll cells, and corre sponded to 80 to 130 mu mol lignin monomers/g needle dry weight. Isoel ectric focusing of apoplastic washing fluids and activity staining wit h guaiacol showed the presence of strongly alkaline peroxidases (isoel ectric point greater than or equal to 9) in all developmental stages i nvestigated. New isozymes with isoelectric points of 7.1 and 8.1 appea red during the major phase of lignification. These isozymes disappeare d after lignification was terminated. A strong increase in peroxidase activity in autumn was associated with the appearance of acidic peroxi dases (isoelectric point less than or equal to 3). These results sugge st that soluble alkaline apoplastic peroxidases participate in lignin formation. Soluble acidic apoplastic peroxidases were apparently unrel ated to developmentally regulated lignification in spruce needles.