Supplementary Fig. 1 Anatomy of phloem. (a) Scots pine seedling. (b) Mature Scots pine. (c) Mature Norway spruce. Squares indicate anatomical regions seen in Figure 1c−e. Double headed arrows in b and c indicate non-collapsed sieve cells (Non-CoSc) and axial parenchyma bands (P_band). Asterisks in c indicate convex cells. Ca, cambium; R, ray parenchyma cell. Scale bars = 100 µm.

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Supplementary Fig. 2 Detection of lignin in mature Norway spruce and Scots pine phloem. Staining with phloroglucinol-HCl (a, c, e) and non-stained controls (b, d, f). Note strong positive staining in stone cells of Norway spruce (d) like in xylem tracheids (X; a, c). Note also negative staining in other cell types including cambium (Ca)-, sieve- (Sc) and axial (P)/ray (R) parenchyma cells. Scale bars = 100 µm.

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Supplementary Fig. 3 Detection of highly methyl-esterified homogalacturonan (HG, LM20) epitopes in phloem cells. (a, c) Mature Norway spruce. (b, d) Mature Scots pine. Note differences in amounts of epitopes between tangential and radial sieve cell walls (Sc) and overall more abundant epitopes in axial/ray parenchyma cells (P/R) than sieve cells. Ca, cambium. Scale bars = 25 µm.

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Supplementary Fig. 4 Detection of heteromannan epitopes in phloem cells. (a, b) Serial sections of mature Norway spruce. Note significant differences in labeling between LM21 (a, considerable amounts)- and LM22 (b, absence) epitopes in sieve cell walls (Sc). Note also abundance of LM21 and LM22 epitopes in xylem tracheids. (c) Mature Scots pine. Note absence of LM22 epitopes in sieve cell walls. (d, e) Norway spruce and Scots pine seedlings. Note some weak LM22 epitopes in early sieve cell wall (asterisks). P, axial parenchyma cells; R, ray parenchyma cells. Scale bars = 50 µm.

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Supplementary Fig. 5 Detection of xyloglucan (LM15) and heteromannan (LM21) epitopes in phloem cells of Norway spruce seedling after pre-treatment with sodium carbonate (Na2CO3) and pectate lyase (PL). Note a slight increase in amounts of epitopes in sections pre-treated with sodium carbonate (b, e) and sodium carbonate + PL (c, f) compared to controls (a, d). Note also similar (LM21) or slightly lower (LM15) levels of labeling intensity in sections pre-treated with PL (c, f) compared to those pre-treated only with sodium carbonate (b, e). Ca, cambium; P, axial parenchyma cell; R, ray parenchyma cell; Sc, sieve cell. Scale bars = 25 µm.

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Supplementary Fig. 6 Detection of xyloglucan (LM15) and heteromannan (LM21) epitopes in phloem cells of Scots pine seedling after pre-treatments with sodium carbonate (Na2CO3) and pectate lyase (PL). Note a slight increase in amounts of epitopes in sections pre-treated with sodium carbonate (b, e) and sodium carbonate + PL (c, f) compared to controls (a, d). Note also similar (LM21) or slightly lower (LM15) levels of labeling intensity in sections pre-treated with PL (c, f) compared to those pre-treated only with sodium carbonate (b, e). Ca, cambium; P, axial parenchyma cell; R, ray parenchyma cell; Sc, sieve cell. Scale bars = 25 µm.