Cell Wall Chemistry and Fine Structure in Leptoids of Dendroligotrichum (Bryophyta): The End Wall

Abstract

Leptoids (sieve elements) of Dendroligotrichum are characterized by a highly oblique end wall which is composed of cellulose (birefringent; IKI‐H2SO4‐positive), polyuronides (toluidine blue‐positive), pectins (hydroxylamine‐positive) and natural aldehydes (silver hexamine and silver proteinate‐positive). Cytochemically the end wall appears identical to the unevenly thickened lateral wall. Electron cytochemical localization of aldehydes with silver proteinate reveals two distinct wall layers in comparison to the 3‐layered lateral wall. Plasmodesmata are present in the end wall with a frequency of 15‐20 per μm2. A characteristic feature of end wall plasmodesmata is an expanded median cavity which is 0.12‐0.15 μm in diameter. Frequently an electron‐dense substance, whose chemical nature and origin are unknown, occludes the plasmodesmata.

Cytoplasmic polarity and endoplasmic microtubules associated with the nucleus and organelles are ubiquitous features of food‐conducting cells in bryoid mosses (Bryophyta)

“…It should be noted, however, that the cytoplasmic sleeve of plasmodesmata, not the desmotubule, is considered to be the more likely route for intercellular symplastic movement of solutes (Lucas, Ding & Van der Schoot, 1993). It may therefore be significant that enlargement of the cytoplasmic sleeve, producing median cavities of varying sizes, is a common feature of plasmodesmata not only in the leptoids of potytrichaceous mosses (Stevenson, 1974;Scheirer 1978Scheirer , 1990) and the food conducting cells of other bryoid mosses (Fig. 6H, G) but also associated with the leaf vasculature of tracheophytes (Lucas et al, 1993).…”

“…1979Scheirer, 1978Scheirer, , 1990Schofieid & 1987) or moss sieve elements (Stevenson, 1977;Hebant, 1984). Scheirer, 1990).…”

Conducting tissues and phyletic relationships of bryophytes

“…100^200 nm wide but usually still constricted at both ends (He¨bant 1976;Scheirer 1978Scheirer , 1990; cf. Lucas et al 1993).…”

Sieve Plate Pores in the Phloem and the Unknowns of Their Formation

“…As previously mentioned, gymnosperms have considerably smaller pores than angiosperms [25]. Intriguingly, just like the Arabidopsis cals7 mutant, not only conifers and cycads but also mosses and some ferns lack callose in their sieve cell end walls and only produce callose upon wounding [70,71,72]. It is, therefore, tempting to speculate that the successive deposition and degradation of callose, which occurs in angiosperms, may have been a key evolutionary invention to allow for larger sieve pores.…”