Microtubule involvement in the deposition of radial fibrillar callose arrays in stomata of the fern Asplenium nidus L.

Abstract

Aniline blue staining and callose immunolabeling revealed the deposition of significant callose quantities, in the form of fibrils, in the periclinal walls of guard cells (GCs) of stomata of the fern Asplenium nidus. The stomata that were at an early stage of differentiation displayed short callose fibrils at the junctions of the periclinal walls with the dorsal ones, which converged on the site of the future stomatal pore. In stomata being at an advanced stage of differentiation, callose fibrils were radially arranged around the stomatal pore, while in mature closed ones they were focused on the margins of the wall thickenings lining the stomatal pore. The pattern of the callose fibril organization resembled that of cellulose microfibrils in the same walls. Like the cellulose microfibrils, callose fibrils appeared coaligned with the underlying radial arrays of cortical microtubules (MTs). Moreover, the stomata treated with cellulose synthesis inhibitors (coumarin or dichlobenil) and those recovering from treatments with callose synthesis inhibitors (2-deoxy-D-glucose or tunicamycin) exhibited distinct radial callose fibril arrays. Cytochalasin B did not affect the organization of the radial callose fibril arrays. In contrast, oryzalin completely disturbed the pattern of callose deposition in the affected GCs. Therefore, the fibrillar callose orientation in the periclinal GC walls is probably controlled by MTs but not by actin filaments. The MTs seem to orient callose synthases in the plasmalemma, thus determining the fibrillar nature of callose deposits and their radial mode of arrangement. The cellulose microfibrils are not involved in the callose fibril alignment.

Callose implication in stomatal opening and closure in the fern Asplenium nidus

“…In paradermal view, the callose deposits appeared as fine fibrillar structures, which, similarly to the cellulose microfibrils, were radially arranged around the stomatal pore region (Fig. 1d; see also Apostolakos et al. , 2009a).…”

“…Fern stomata display intense callose depositions in GC walls (Peterson et al. , 1975; Peterson & Hambleton, 1978; Waterkeyn & Bienfait, 1979; Apostolakos & Galatis, 1999; Apostolakos et al. , 2009a,b).…”

“…Moreover, in the periclinal walls of differentiating GCs of this fern, callose is polymerized in the form of fibrils radially arranged around the stomatal pore. Radial callose arrays were also found in closed functioning stomata (Apostolakos et al. , 2009a).…”

Biotechnological aspects of cytoskeletal regulation in plants

“…In general callose is composed of β(1 → 3) glucan polymer chains and it is produced in response to wounding but also as a cell wall precursor of the growing cell plate at the end of cell division. In tobacco pollen tube callose synthases are transported and incorporated to membrane areas by actin and microtubule arrays (Cai et al, 2011) while in ferns, callose deposition seems to coincide with radial cortical microtubule arrangements in differentiating stomatal guard cells (Apostolakos et al, 2009). 9.4.…”

How do microtubules affect deposition of cell wall polysaccharides in the pollen tube?

“…disrupted the pattern of callose deposition, it is likely that the orientation of callose in the periclinal walls is controlled by MTs. 21 Treatment with oryzalin also inhibits callose synthase activity in Arabidopsis and tobacco cells, showing that intact MTs are required for the appropriate quantitative synthesis of callose. 22 These few evidences indicate that the organization pattern of cortical MTs is critical for the correct activity of CalS and imply that MTs might either affect the precise positioning of CalS or regulate its enzyme activity (or both).…”