Abstract
Hechtian strands are thread-like structures in plasmolyzed plant cells that connect the cell wall to the plasma membrane. Although these strands were first observed more than 100 years ago, their physiological roles are largely unknown. Here, we used intracellular laser microdissection to examine the effects of disrupting Hechtian strands on plasmolyzed tobacco BY-2 cells. When we focused femtosecond laser pulses on Hechtian strands, targeted disruptions were induced, but no visible changes in cell morphology were detected. However, the calcofluor white signals from β-glucans was detected in plasmolyzed cells with disrupted Hechtian strands, whereas no signals were detected in untreated plasmolyzed cells. These results suggest that Hechtian strands play roles in sensing cell wall integrity.
Highlights
Under high osmotic conditions, plant cells lose water and shrink, causing the plasma membrane to detach from the cell wall
Hechtian strands were first observed more than 100 years ago [1], our knowledge of their physical properties is limited to the following findings: 1) Hechtian strands are 30 to 250 nm in diameter [3,6]; 2) the length and density of these strands vary depending on the cell and experimental condition [1,2,3,4,5,6,7,8,9]; and 3) the density, length, and tension of Hechtian strands can be altered by cold hardening treatment [9,10]
Biochemical assays indicated that Hechtian strands contain cytoplasm and/or endoplasmic reticulum (ER) in their interior regions [3,11,12], and the constricted tubule of ER has been proposed to run through each Hechtian strand and possibly connect to the plasmodesmata [13]
Summary
Plant cells lose water and shrink, causing the plasma membrane to detach from the cell wall. Specific proteins linking the cell wall and plasma membrane, such as glycosylphosphatidylinositol (GPI)-anchored arabinogalactan proteins [15,16], cell wall associated kinases [17], and integrin-like RGD-binding proteins [18,19], can be involved in Hechtian strand formation. These observations suggest that Hechtian strands form physical connections between the plasma membrane and cell wall, and mechanically transduce cell wall stress signals to receptors located in the plasma membrane [8,20,21]. The results of this study, representing the first study of the in vivo effects of the physical destruction of Hechtian strands, suggest the possibility that Hechtian strands transduce cell wall integrity signals between the plasma membrane and cell wall
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