Cytoskeleton as a generator of characteristic physical properties of plant cells: 'cell wall,' 'large vacuole,' and 'cytoplasmic streaming'

Abstract

As sessile organisms, plants must constantly adapt to ever-changing environmental conditions. To survive in their habitats, plants have evolved characteristic cellular features that make the cells rigid yet dynamic. These include the cell wall, large vacuole, and cytoplasmic streaming. The cell wall is an elaborate extracellular matrix that surrounds plant cells and provides both physical strength and protection against external forces. The large vacuole is a membrane-bound organelle absent in animal cells. They can absorb water and expand, thereby exerting a force on the cell wall from within and generating turgor pressure that promotes cell expansion. In the narrow cytoplasmic space between the vacuole and the cell wall, intracellular components circulate via rapid flows, a phenomenon known as cytoplasmic streaming. In this review, we summarize how these three characteristic features of plant cells are organized with the help of cytoskeletal elements. This review article is an extended version of the Japanese article, "Cell Wall," "Large Vacuole," & "Cytoplasmic Streaming": How Do Cytoskeletons Build Plant Cells with Unique Physical Properties?" by Takatsuka et al., published in SEIBUTSU BUTSURI Vol. 64, p. 132-136 (2024).

Keywords: cell wall; cytoplasmic streaming; cytoskeleton; plant cell; vacuole.

Figure 1

Structure of the plant cell with its characteristic physical properties. Plant cells are enclosed by rigid cell walls and harbor the large vacuole that generates large turgor pressure. Despite these structural constraints, cytoplasmic streaming is believed to play a crucial role in facilitating the circulation and distribution of cellular substances.

Figure 2

Organization of the cell walls and cytoskeletons in elongating root cells. (A) An undifferentiated cell just after division (left) and a fully differentiated cell (right) from the root epidermis of Arabidopsis thaliana. Cell outlines were visualized using propidium iodide. Scale bars represent 5 μm (left) and 100 μm (right). (B) In root cells elongating longitudinally, cellulose microfibrils align transversely at the cell cortex, restricting lateral expansion and supporting directional growth. (C) Immunofluorescence images of a growing root cell of Arabidopsis thaliana simultaneously stained with anti-tubulin and anti-actin antibodies. MTs are oriented transversely (left), while AFs are oriented longitudinally (middle). The merged image is shown on the right. Scale bar: 10 μm.

Figure 3

Large vacuoles in plant cells and their dynamics during stomal opening and closing. (A) A ransmission electron micrograph (TEM) of a root epidermal cell of Arabidopsis thaliana. The cell outline was traced with dotted yellow lines. The scale bar represents 10 μm. n: nucleus (shown in blue), v: vacuole (shown in white). (B) Dynamics of AFs and vacuoles during stomatal opening and closing.

Figure 4

Hypothetical models of actomyosin-driven cytoplasmic streaming. Red arrows indicate the direction of myosin movement along AFs, while grey arrows represent the resulting cytoplasmic flow.