Search

The anatomical response of Norway spruce bark polyphenolic parenchyma cells (PP cells) to inoculation with the phytopathogenic fungus Ceratocystis polonica and attack by its bark-beetle vector Ips typographus was examined. Fungal inoculation on the periderm surface had no effect, while inoculation just below the periderm or halfway into the phloem (mid-phloem) generated detectable responses within 3 wk. The responses included increase in PP cell size and in periodic acid-Schiff's staining of PP cell phenolics, wound periderm initiation from PP cells, and cambial zone traumatic resin duct formation. Fungi were not seen in samples 3 wk after subperiderm or mid-phloem inoculation, but were found in some samples 6 and 9 wk after mid-phloem inoculation. In contrast, inoculations into the cambium resulted in partial (3 wk) or complete (6 and 9 wk) fungal colonization and death of tissue in the infected area. This indicates that PP cells have defenses capable of inhibiting fungal growth. Samples taken near bark-beetle galleries had similar anatomical responses as inoculated samples, validating the inoculation approach to studying defense responses in spruce. These results show that PP cells represent not only a constitutive defense system, but are also involved in local and remote inducible defenses against fungal and beetle attack.