Fig 12. Cell architecture of beech (Fagus grandifolia) leaves.

Photomicrographs of transverse sections of control and symptomatic beech leaf disease (BLD) leaves collected in early autumn. Sections were stained with a mixture of hematoxylin and eosin. (A) Representative control beech leaf. (B-C) Section of a mature control beech leaf showing differentiated cell layers as indicated in figure C. (D) Representative symptomatic BLD leaf. Dotted white, blue and orange squares represent sections of (G) asymptomatic, (H) green and (E-F) yellow banded areas of the same leaf used for histological analyses. (E-F) Sections of yellow symptomatic BLD areas showing extensive leaf thickness as a consequence of cell proliferation and cell hypertrophy. Nematode sections are stained (dark purple). (G) Section of a non-symptomatic area of a BLD leaf, which presents cell architecture similar to that of control leaves (B). (H) Section of a green interveinal area of a BLD leaf without nematodes. Note the additional cell layers in comparison to the control leaves (C). (I) Leaf thickness was measured from photomicrographs of control, asymptomatic (BLD_a) and symptomatic BLD areas without (BLD -n) and with (BLD +n) nematodes. For each condition a minimum of 50 measurements were made. (J-L) Cell surface (μm²) was measured for the upper epidermis (J), lower epidermis (K) and spongy mesophyll cells (L). Measures were made for control (n = 80 cells), asymptomatic (BLD_a, n = 100 cells) and symptomatic BLD areas without (BLD -n, n = 100 cells) and with (BLD +n, n = 100 cells) nematodes. Thick lines in the boxplot represent medians. Different letters denote statistical differences between cell sizes (P < 0.05, ANOVA with Tukey-Kramer test). Scale bars: 100 μm (A, B); 50 μm (C-H).