Figure 2.

Stem cross-sections of 2-year-old Norway spruce plants collected 9 weeks after the start of the experiment. (A) Untreated control plant with phloem (Phl), containing a large cortical resin duct (CD), and three annual rings of xylem growth (Yr, Yr-1, Yr-2). Scattered resin ducts (white arrowheads) are visible in the Yr-1 annual ring (Yr-1). (B) Plant treated with 100 mM methyl jasmonate (MeJA) 9 weeks earlier. An almost continuous ring of traumatic resin ducts (triple black arrowheads) is visible in the current annual xylem growth, which is much narrower than in the control. (C) Higher magnification of A showing sieve cells interspersed with rounded parenchyma cells with vacuolar polyphenolic inclusions in the phloem (small yellow circles). (D) Higher magnification of B showing traumatic resin ducts with very wide lumens and coalescence of adjoining ducts. (E) Untreated control plant that was inoculated with the fungus Endoconidiophora polonica 4 weeks after the start of the experiment. (F) Plant treated with 50 mM MeJA 9 weeks earlier has numerous traumatic resin ducts and normal annual xylem growth. (G) Plant treated with 200 mM oxalic acid 9 weeks earlier. (H) Plant treated with 5 mM MeJA 9 weeks earlier has extensive traumatic resin duct formation and normal annual xylem growth.