Fig. 2

Histochemical evaluation of the lignified nature of peach and walnut endocarps. Evaluation of endocarp used the anatomically characterized Arabidopsis stem section from the lower stem (before first leaf) that have primary and secondary cell walls developed. mx metaxylem, phl phloem, te tracheary elements, ep epidermis (note that the cortex is not well defined and grouped with the epidermis), mx-l metaxylem-like staining. A Toluidine blue staining of transverse cross sections of Arabidopsis stem tissue revealed clear demarcation of the metaxylem in blue, which was also reflected as being highly lignified in the phloroglucinol (B) stained stem cross section due to its cherry red color. The switchgrass and pine shavings stained with toluidine blue (C, E) display a metaxylem-like tissue at a very similar capacity when compared to peach and walnut (G, I). Phloroglucinol staining displays a marked increase in lignin abundance within the peach and walnut endocarps (H, J) when compared to the switchgrass and pine samples (D, F). Scale Bars (100 µM = C, G, I, J/200 µM = A, B, E, F, H/500 µM = D). Magnification (×2 = D/×4 = E, F/×5 = A, B, H/×6.3 = C, G, I, J)