Phloem parenchyma cells are involved in local and distant defense responses to fungal inoculation or bark-beetle attack in Norway spruce (Pinaceae)

The anatomical response of Norway spruce bark polyphenolic parenchyma cells (PP cells) to inoculation with the phytopathogenic fungus Ceratocystis pol onica and attack by its bark-beetle vector lps typographus was examined. Fu ngal inoculation on the periderm surface had no effect, while inoculation j ust below the periderm or halfway into the phloem (mid-phloem) generated de tectable responses within 3 wk. The responses included increase in PP cell size and in periodic acid-Schiff's staining of PP cell phenolics, wound per iderm initiation from PP cells, and cambial zone traumatic resin duct forma tion. Fungi were not seen in samples 3 wk after subperiderm or mid-phloem i noculation, but were found in some samples 6 and 9 wk after mid-phloem inoc ulation. 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 inhib iting fungal growth. Samples taken near bark-beetle galleries had similar a natomical responses as inoculated samples, validating the inoculation appro ach to studying defense responses in spruce. These results show that PP cel ls represent not only a constitutive defense system, but are also involved in local and remote inducible defenses against fungal and beetle attack.