Hyperosmotic Stress Induces Formation of Tubulin Macrotubules in Root-Tip Cells of Triticum turgidum: Their Probable Involvement in Protoplast Volume Control

Abstract

Treatment of root-tip cells of Triticum turgidum with 1 M mannitol solution for 30 min induces microtubule (Mt) disintegration in the plasmolyzed protoplasts. Interphase plasmolyzed cells possess many cortical, perinuclear and endoplasmic macrotubules, 35 nm in mean diameter, forming prominent arrays. In dividing cells macrotubules assemble into aberrant mitotic and cytokinetic apparatuses resulting in the disturbance of cell division. Putative tubulin paracrystals were occasionally observed in plasmolyzed cells. The quantity of polymeric tubulin in plasmolyzed cells exceeds that in control cells. Root-tip cells exposed for 2-8 h to plasmolyticum recover partially, although the volume of the plasmolyzed protoplast does not change detectably. Among other events, the macrotubules are replaced by Mts, chromatin assumes its typical appearance and the cells undergo typical cell divisions. Additionally, polysaccharidic material is found in the periplasmic space. Oryzalin and colchicine treatment induced macrotubule disintegration and a significant reduction of protoplast volume in every plasmolyzed cell type examined, whereas cytochalasin B had only minor effects restricted to differentiated cells. These results suggest that Mt destruction by hyperosmotic stress, and their replacement by tubulin macrotubules and putative tubulin paracrystals is a common feature among angiosperms and that macrotubules are involved in the mechanism of protoplast volume regulation.

Hyperosmotically induced accumulation of a phosphorylated p38‐like MAPK involved in protoplast volume regulation of plasmolyzed wheat root cells

“…Transmission electron microscopy and tubulin polymer morphometric analysis Root tips were fixed, dehydrated, infiltrated and embedded in Spurr's resin as previously described [13]. Thin sections were sequentially stained with uranyl acetate and lead citrate and observed through a Philips 300 EM.…”

“…Thin sections were sequentially stained with uranyl acetate and lead citrate and observed through a Philips 300 EM. For Mts and macrotubule diameter measurements, the microscope was calibrated with a grated microscale and measurements were conducted accordingly [13].…”

“…The time course of plasmolysis of wheat root cells in hyperosmotic sucrose was essential as described for mannitol solutions [13]. In untreated roots, plasmolysis was concluded within 5-10 min after the exposure of root cells to the hyperosmotic medium.…”

“…Additionally, its involvement in the tubulin cytoskeleton-dependent-mechanism of the protoplast volume regulation previously described in wheat roots [13] was investigated.…”

The Arabidopsis Synaptotagmin1 Is Enriched in Endoplasmic Reticulum-Plasma Membrane Contact Sites and Confers Cellular Resistance to Mechanical Stresses

“…In such a structure, the mechanical disturbance of any individual element allows stress signals to propagate and be transduced at relatively distant locations (Ingber, 2008). Thus, the mechanically stable cell walls provide structural support, and the constant remodeling of the underlying cytoskeleton in response to mechanical disturbances acts as a tensegrity sensor (Komis et al, 2002;Berghöfer et al, 2009;Nick, 2013).…”