Figure 9.

MYB46 Overexpression Causes Ectopic Deposition of Secondary Walls in the Parenchyma Cells of Inflorescence Stems and Results in an Increased Secondary Wall Thickening in Vessels.

Stems of 8-week-old plants were used for examination of secondary wall thickening by toluidine blue or phloroglucinol-HCl staining. co, cortex; ep, epidermis; if, interfascicular fiber; ph, phloem; ve, vessel; xf, xylary fiber. Bars = 66 μm in (A), (B), (E), (F), (I), and (J), 39 μm in (C) and (D), and 8 μm in (G), (H), (K), and (L).

(A) and (B) Cross sections of stems showing ectopic deposition of thick secondary walls in cortical cells (arrows and asterisk) and epidermis (arrowheads) in the MYB46 overexpressors (B) compared with the wild type (A). Note that some cortical cells showed reticulated secondary wall thickening (arrows), and the walls of some cortical cells (asterisk) are thicker than those of interfascicular fibers.

(C) and (D) Phloroglucinol-HCl staining of the epidermal peels of stems showing the ectopic deposition of lignified secondary walls (inset) in the MYB46 overexpressors (D) compared with the wild type (C).

(E) and (F) Longitudinal sections of cortical regions showing that the thick-walled cortical cells (arrows) in the MYB46 overexpressors (F) had similar length as those of the wild type (E).

(G) and (H) Transmission electron micrographs of cortical cells showing their thick walls (asterisk) in the MYB46 overexpressors (H) compared with the wild type (G).

(I) and (J) Cross sections of vascular bundles of the wild type (I) and MYB46 overexpressors (J).

(K) and (L) Transmission electron micrographs of xylem showing an increase in secondary wall thickening in the vessels of MYB46 overexpressors (L) compared with the wild type (K).