Calcium carbonate deposition in a cell wall sac formed in mulberry idioblasts

Abstract

Although calcium carbonate is known to be a common biomineral in plants, very little attention has been given to the biological control of calcium carbonate deposition. In mulberry leaves, a subcellular structure is involved in mineral deposition and is described here by a variety of cytological techniques. Calcium carbonate was deposited in large, rounded idioblast cells located in the upper epidermal layer of mulberry leaves. Next to the outmost region ("cap") of young idioblasts, we found that the inner cell wall layer expanded to form a peculiar outgrowth, named cell wall sac in this report. This sac grew and eventually occupied the entire apoplastic space of the idioblast. Inside the mature cell wall sac, various cellulosic membranes developed and became the major site of Ca carbonate deposition. Concentrated Ca2+ was pooled in the peripheral zone, where small Ca carbonate globules were present in large numbers. Large globules were tightly packed among multiple membranes in the central zone, especially in compartments formed by cellulosic membranes and in their neighboring membranes. The maximum Ca sink capacity of a single cell wall sac was quantified using enzymatically isolated idioblasts as approximately 48 ng. The newly formed outgrowth in idioblasts is not a pure calcareous body but a complex cell wall structure filled with substantial amounts of Ca carbonate crystals.

Ultrastructural and immunochemical features of the cell wall sac formed in mulberry (Morus alba) idioblasts

“…The epidermal idioblasts develop a cell wall sac that is a deposition site of CaCO 3 crystals (Sugimura et al 1999). The role of CaCO 3 production is thought to be regulation of bulk Ca 2+ levels in leaf tissues because of the high Ca sink capacity accommodated in the single sac (Nitta et al 2006). Although ultrastructural changes during the sac formation have been observed previously (Nitta et al 2006;Sugimura and Nitta 2007), no information is available on the disassembly of cell wall polysaccharides in relation to cell wall sac formation.…”

“…For light microscopic observation, semithin sections were stained with 0.01% (w/v) toluidine blue. For electron microscopic observation, ultra-thin sections were sequentially stained with uranyl acetate and lead citrate (Nitta et al 2006). After drying, the sections were examined with an electron microscope (JEM-1220; Jeol, Japan) operating at 80 kV.…”

“…In mulberry leaves, idioblasts situated in epidermal layer develop a bulbous structure filled with substantial amounts of amorphous CaCO 3 crystals (Sugimura et al 1998(Sugimura et al , 1999. The structure is not a pure calcareous body but a subcellular structure named a ''cell wall sac'' (Nitta et al 2006). This sac formation is likely to be induced by the site-specific activation of cell wall-degrading enzymes (Sugimura and Nitta 2007) and to play important physiological roles in bulk Ca 2+ regulation (Nitta et al 2006).…”

“…The structure is not a pure calcareous body but a subcellular structure named a ''cell wall sac'' (Nitta et al 2006). This sac formation is likely to be induced by the site-specific activation of cell wall-degrading enzymes (Sugimura and Nitta 2007) and to play important physiological roles in bulk Ca 2+ regulation (Nitta et al 2006).…”

Calcium promotes cadmium elimination as vaterite grains by tobacco trichomes

“…In Plantae, it is biosynthesized in few families, such as Moraceae, Urticaceae, and Acanthaceae, generally occurring as intercellular concretions (cystolith) (Arnott and Pautard, 1970;Setoguchi et al, 1989;Nitta et al, 2006). In contrast to calcium carbonate in animals, calcium oxalate is probably the most commonly formed mineral in higher plants (Franceschi and Homer, 1980).…”