Jurnal Riset Biologi dan Aplikasinya, Volume XXXX Issue XXXX, XXXX Jurnal Riset Biologi dan Aplikasinya https://journal.unesa.ac.id/index.php/risetbiologi The Relationship Between Turgor Pressure and Growth in Plants Nurul Jannah*, Wan Syafi’i Universitas Riau Kampus Bina Widya Km 12,5 Simpang Baru, Pekanbaru, Indonesia * [email protected], [email protected] ABSTRACT Biomechanical studies also state that plant growth primarily focuses on primary cell wall expansion caused by turgor pressure. For this reason, it is necessary to analyze the relationship between turgor pressure and plant growth. The method in writing this article with descriptive analysis on various sources in the form of books and international journals. The relationship between turgor pressure and plant growth includes the role of structural integrity in each cell and tissue, cell wall formation, seed development and also the process of pollination in flowers. The existence of the influence of turgor pressure is attributed to the mechanical models of Lockhart's and Young-Laplace. It can be concluded that there is a relationship of turgor pressure on plant growth with various mechanical models and research on plant organs, especially in flowers. Keywords: turgor, growth, mechanical, development, cell wall. INTRODUCTION Plant cells often have intracellular osmolytes that cause them to stiffen but not break. If the cell lacks the osmolyte, the cell will shrink and lose rigidity. Researchers biophysicists often analogize the rigidity of cells such as The Shape of a balloon or bubble that has a boundary between the inside and outside of the balloon. In this case, the cell has a cell wall that is the delimiter and determinant of the rigidity of a cell. In addition, the cell wall is also an important part in cell growth. Biomechanical studies also state that plant growth mainly focuses on the expansion of the primary cell wall caused by mechanical stress and stress. Expansion walls are often thought of as passive or protein-mediated stress relaxation, whichoccurs through de novo synthesis of wall materials and / or wall renovation (Cosgrove, 2022). Research conducted by (Haas et al., 2020) suggested that some cells with walls such as Arabidopsis cells expand rapidly during the plasmolysis process due to swelling of pectin nanofilaments. Anisotorphic and isotropic arrangement of shoot tip shapes is also the result of 1 mechanical stress on epidermal tissue (Hunt et al., 1990). This pressure is often considered a biophysical parameter that is passive and constant at the beginning of growth and maintains the expansion of the wall. Research conducted by (Ali et al., 2023) that biologically active turgor regulates cell growth. For this reason, it is necessary to analyze the relationship between turgor pressure and growth in cells Especially in the early cell formation of plant organs such as the formation of leaves and flowers. MATERIAL AND METHODS The method used is literature study. The literature used is in the form of international journals, articles, and books on plant growth and development. Then an analysis of the material turgor pressure and summarized into a scientific journal. RESULTS AND DISCUSSION Turgor Pressure Turgor pressure is a variable adjustable through osmosis by increasing or decreasing the concentration of osmolytics such as ions, carbohydrates, and amino acids in the cytoplasm and vacuoles. The water content can also be regulated more directly by adjacent cells. Water transport proteins (aquaporins) regulate most of the water transport across the plasma membrane. Turgor pressure provides structural integrity to each cell and tissue as a whole (Figure 1). At the cellular level, turgor pressure pushes the plasma membrane towards the cell wall and causes mechanical stress in the cell wall (Figure 1a). The rigid cell wall, which consists of a complex mixture of Carbohydrate Polymers and structural proteins, stretches until it reaches a size and shape in which the cell wall can stably withstand internal stresses (Robinson et al., 2013). The rigidity of a cell comes from the properties of the cell wall material and the turgor pressure inside the cell. In highly turgid cells, surface stiffness is largely determined by pressure. Similarly, at the tissue level, the structural strength of the tissue depends on the stiffness of the cell walls and the turgor pressure within each cell. It is easy to observe that the network network it hardens when turgor pressure increases and becomes flabby and even withers when turgor pressure decreases. Turgor is therefore essential for the morphology, architecture and engineering robustness of plants. It is also believed that the outermost structures of the air organs are under tension and resist internal pressure the resulting pressure from the internal cells is borne by the epidermal cells, especially the outermost cell walls at the tissue surface (Robinson et al., 2013) ( 1B). 2 Figure 1. Turgor Pressure and its Molecular Determinants. (A) Turgor pressure results in the tension of the cell wall. (B) Turgor pressure can induce tension at the tissue level, as seen in the epidermis, for example. (C) Turgor pressure and water flow are contingent on plasmodesmata, aquaporins, transporters, and channels. Given the role of turgor pressure in the structural strength of plants, it is not surprising that dynamic variations in turgor pressure have been associated with plant movement for example in the circadian movement of leaves. The most studied example is the stomata, which only open when the turgor pressure is high enough on the guard cells.In addition to the structural contribution, turgor pressure also affects the physical condition in the cell and subsequently Cellular and biochemical functions. This causes the plasma membrane to compress the cell wall and reduce the thickness of the cell merman. Increased cellular hydraulic pressure is often associated with increased cytoplasmic concentrations such that cytoplasmic crowding alters conformation and macromolecular interactions. Dynamics of intracellular membranes, as well as the size and shape of organelles, too,appear to be sensitive to turgor pressure; for example, th higher the turgor pressure, the higher the energy barrier for endocytosis to occur. (Beauzamy et al., 2014). In addition, changes in turgor pressure may be involved in signal transduction pathways. Environmental conditions affect turgor pressure; high salinity or water stress reduces turgor, while hypo-osmotic conditions (such as in floods) and pressure from being stepped on by animals or bending by the wind, for example, will increase pressure. Biotic stress, for example a wound caused by a microbial infection, can release turgor pressure. Therefore, some of these signal 3 transduction and molecular pathways are activated in response to environmental stress from cues associated with changes in turgor pressure or other mechanical changes (Walley et al., 2007). Basically the osmotic condition of the cell is so closely related to turgor pressure that it is often thought that the cell measures intracellular pressure through osmosensing. Cells are thought to be able to detect turgor pressure from their expansion or shrinkage after a change in internal pressure. A mechanosensitive Protein that is embedded in the plasma membrane and is active when the cell is deformed. For example in a strain-activated channel it can indirectly trigger a response to a change in turgor. There are many ways in which cells detect physical parameters such as turgor pressure; virtually every diverse way in which turgor pressure can affect a cell, as described above, can be an input to induce a cellular response. In this case turgor would be at once the Integrating of environmental and developmental cues and the entry point for various signaling pathways (Beauzamy et al., 2014). Here is a picture of the difference in osmotic pressure in a cell bounded bycell wall. Figure 2. Hydraulics and mechanics of plant cells. (A) Panel atas: Diferensial osmolaritasbetween the cell (left side) and the extracellular medium (right side), separated by a semi-permeable plasma membrane (thin ivory-colored line) and a cell wall (thick pink line), causes a flow of water (J osm ) to the compartment withthe highest osmolarity. Middle Panel: this water Influx increases the pressure hydrostatic cells (P) which in turn produce a flow of water to the right side (J hydro). Bottom Panel: deformation of the cell wall leads to accumulation of tensile stress ( ) within the wall, which balances the hydrostatic pressure exerted on the wall. (B) the hydrostatic pressure (P) in an ideal spherical plant cell immersed in a spherical wall with Radius and thickness produces a tensile pressure ( wall according to the Young-Laplace equation. 4 ) in the Cell Wall Interaction with Turgor Pressure Plant cells are surrounded by a rigid cell wall that must be able to withstand significant turgor pressure inside. Plant cell walls are also dynamically expandable, as cells can grow rapidly to much larger sizes. Growth in plants is simplastic; cells are bound to each other and cannot move relative to each other. This explains that the shape and structure of plantsarise from the regulated growth of cell walls. Understanding how genes perform this regulation, and their interactions with cell wall mechanics, requires methods for measuring mechanical properties at the cellular level (Hunt et al., 1990). Growth is triggered by cellular turgor pressure, which induces tensile stress on the surrounding cell walls. The cell wall is a complex polysaccharide structure made of strong cellulose microfibrils embedded in a highly hydrating matrix made of polysaccharides such as hemicellulose (especially xyloglucans), pectin, and other structural. During plant cell growth, the elastic strain on the cell wall caused by turgor pressure becomes irreversible, as the interactions between the various polysaccharides in the wall undergo modification in a process called remodelling. Simultaneously with the biosynthesis of new wall components, these processes determine the rigidity of the cell wall and its ability to grow. Turgor pressure Model in plantsLockhart's Model explains that in plant cells, growth depends on osmotic water absorption and cell wall expansion. This process is often described as an irreversible viscoplastic yielding mechanism. The relationship between cell growth rate and turgor pressure relies on a balance between osmotic pressure and cell wall yield threshold, as described in the Lockhart equation in the case of elongated cylindrical cells. Here's the Lockhart model : One of the main results of Lockhart's model is that turgor pressure is not a variable that controls growth. Turgor pressure is controlled by osmotic potential, cell wall yield threshold, and balance between elasticity and conductance. This equation shows that turgor and growth are the result of a complex interaction between flow and wall expansion, and the two are not always definitively correlated. The mechanisms underlying growth rate and turgor pressure are proportional at spatial resolution. Therefore, turgor is not a major determinant of growth rate, but rather an emergent property of this system that is closely related to growth (Ali et al., 2023). In many cases, plant cells not only undergo elongation as described in Lockhart's model, but also tend to adopt a more rounded shape. Although it is often compared to a soap bubble due to its depressed state, the analogy is inappropriate because the cell wall is not like a liquid 5 membrane. The mechanics of plant cells can be more accurately understood through the pressurized shell model (Ali et al., 2014). Although different, the pressurized shell and the bubble have something in common: the relationship between their shape, the internal pressure (P) and the tensile stress (σ) at mechanical equilibrium. In the simple case of isotropic and homogeneous spherical shells, this relationship is expressed in the Young-Laplace equation: where R indicates the radius of the cell, h, wall thickness (Figure 1B), and when the external pressure is zero. If the thickness is fixed, this equation implies that the ratio is proportional and constant in the elongated cylinder in Lockhart's model. To evaluate the consequences of this difference, consider two extreme situations: first, if the pressure is constant due to the presence of a rapid flow, the stress will increase with the size of the cells. Explains that plants form puzzleshaped cells in the leaves, due to the non-spherical shape to reduce stress on the cell walls. From a mechanosensitive point of view, stress on the cell wall is used to "measure" their shape and size, which becomes an information for the cells. Secondly, if the stress remains constant, then the turgor pressure will decrease with size. In general, the growing tissue can be in one of the states described above, or somewhere in between. Therefore, the size and shape of the growing cell can affect turgor pressure, wall stress, and growth. At the organ level, the impact of pressure on deep tissues on organ growth has been investigated in developing seeds. In this case, the hydrostatic pressure of the endosperm, a zygotic compartment that dominates the seed's internal space in the early stages, plays an important role in seed (Beauzamy et al., 2014). The pressure on the endosperm decreases as it enters its final stage of growth. This pressure also creates tension in the testa, which is the growing layer of seed coat. It is thought that this stress can be perceived by a special coating inside the testa, which then leads to hardening of the walls and limits growth. Through modeling and experimental approaches, this study shows that endosperm pressure initially favors seed growth but also limits growth by triggering testa hardening. Thus, a decrease in endosperm pressure during the final growth phase does not trigger growth arrest, but rather allows for longer seed growth by preventing premature hardening of the testa (Reproduction & Lyon, 2021). This study illustrates the importance of turgor pressure regulation during organ growth, although the mechanisms involved are still unsolved. 6 Turgor Pressure In Flowers The opening of the flower is usually quick and is completed within 5-30 minutes. In most species, the opening occurs due to the opening of The Calyx (that is, the removal of physical obstacles, for example, through abscission of the bracts and sepals) or the movement of The Calyx. The movement of the petals can be controlled through cell expansion or shrinkage through osmoregulation. For example, the petals of Gentiana kochiana and Kalanchoe blossfeldiana move through reversible cell expansion and contraction, which is driven by turgor on the adaxial surface (Beauzamy et al., 2014) The petals of the Morning Glory flower (Ipomoea tricolor) open in the morning and experience senescence in the afternoon of the same day. Senescence begins by rolling the petals, arching the ribs starting from the distal end. This process is induced by ethylene, which increases the outgoing effusion of ions (Rb+) and sucrose from the ribs; rolling can be caused by asymmetric changes in turgor, as The Calyx can be rolled back when turgor pressure is removed in a strong hyperosmotic treatment that causes cell plasmolysis (Beauzamy et al., 2014) Aquaporins play a central role in Petal cell expansion, and they mediate ethylenedependent inhibition of flower opening. In roses, ethylene inhibits or promotes the growth of petals depending on the variety and in the 'Samantha' variety, ethylene negatively regulates petal expansion. Ethylene treatment resulted in irregular and smaller petals due to less cell expansion and lower water content, and the aquaporin genes PIP1;1 and PIP2;1 were found to have decreased expression (Chen et al., 2013). Pollen Tube Growth When plants are ready for reproduction, the anthers open to expose and release mature pollen. This process is called anther dehiscence, and in many species it is the temporal determinant. of pollination and subsequent fertilization. Anther dehiscence is thought to result from a refined sequence of water allocation within the stamen (Fig. 3A); the endothecium (the sub-epidermal tissue) and other specific cell types are actively hydrated first and then dehydrated during the final stages of stamen differentiation (Scott et al., 2004). When pollen falls on the stigma at the end of the carpel, it swells in one position and begins to lengthen into a tube. The pollen tube is an extrusion of the vegetative cell tube of a microgamefite, carrying two sperm cells inside it and extending inside the carpel stylus to carry sperm to the megagametophyte for fertilization. The pollen tube is an autonomous single-cell system that undergoes localized growth at the tip once, a type of cell growth called 'tip growth' (Figure 3C), which is also found in fungal hyphae and hair roots. 7 The pollen tube is one of the most researched systems in plant cell biology, especially in cell growth regulation research. Figure 3. Case studies in flowers. (A) Dehisensi Anter. ( B) Expansion Of The Crown. (C) Growth of Pollen Tubes. Growth is driven by turgor pressure, and the pollen tube is one of the fastest growing cells (Sanati Nezhad and Geitmann, 2013). Pollen has a high content of proline and hydroproline (0.14% of soluble molecules) at the end. When plasmolysis begins at the end in hyperosmo treatment it is argued that the incoming/outgoing flow is limited to the growing end, plasmolysis usually begins at the corners of the cell. Turgor pressure becomes the main driver especially in the context of oscillatory growth of pollen tubes. Although the pollen tube initially grows stably, it often switches to oscillatory growth over time, especially when it grows too fast or experiences instability. The pollen then oscillates between the fast and slow growth phases, repeating the shift between growth promotion and inhibition every few minutes. Thus, oscillatory growth allows a more detailed analysis of the time sequence of factors affecting growth regulation. During the oscillatory growth phase, the concentration of osmotic solutes such as Proline also fluctuates. Although the inflow of ions such as K+ and Ca2+ also undergoes oscillations, the peak is more likely to precede the slow growth phase than rapid growth phase. Importantly, there is no consistent, oscillationdependent variation in turgor pressure measured on lily pollen tubes by (Benkert et al., 1997) Cells that undergo Plasmolysis and lose turgor pressure cannot undergo growth, it can be concluded that there is a certain threshold turgor pressure required to support growth. However, on the contrary, excessive turgor pressure, reaching about twice the normal level, can lead to rupture of the pollen tube at its tip(Benkert et al., 1997). Therefore, perhaps the role of 8 turgor pressure in growth is related to its calibration to a certain range that is critical for the maintenance of growth. One of the models to measure turgor pressure in plants is the Osmosensor model. An Osmosensor located on the plasma membrane at the growing end of the pollen tube detects the difference in osmotic pressure between the cytoplasm and the apoplast, regulating the inflow of water. Because osmosensors show sensitivity to treatment with mercury (as an inhibitor of aquaporins), there is a hypothesis that aquaporins can act as osmosensors. In fast-growing cells such as pollen tubes, the elasticity of the cell wall can reach significant levels, so that the turgor pressure remains stable close to the yield pressure required for growth. This can explain that no turgor pressure oscillations are observed. Changes in growth rate can be more due to changes in hydraulic conductivity or osmotic potential, without the needto regulate turgor pressure (Beauzamy et al., 2014). Conducted pressure probe measurement of lily pollen tubes, being able to keep a micropipette inserted for 20– 30 min without affecting the growth significantly. The turgor was measured in the range 0.1–0.4 MPa, about .21 MPa on average. They also estimated the turgor pressure within the tube using incipient plasmolysis and found the mean to be 0.79 MPa. This discrepancy might be ascribed to the limitations of the incipient plasmolysis technique, e.g. cells could osmoregulate upon hyperosmotic treatments.(Benkert et al., 1997) CONCLUSION Turgor pressure in plants has a role in growth, namely as a regulator of cell shape with a model that has been studied by experts. Turgor pressure is also a benchmark for seed development at the beginning of development as well as the pollination process that occurs in flowers. For this reason, further research is needed on how turgor pressure can regulate the growth process in plants. REFERENCES Ali, O., Cheddadi, I., Landrein, B., & Long, Y. (2023). Meninjau kembali hubungan antar turgor tekanan dan pertumbuhan sel tanaman. New Phytologist, 238(1), 62–69. Ali, O., Mirabet, V., Godin, C., & Traas, J. (2014). Physical models of plant development. Annual Review of Cell and Developmental Biology, 30, 59–78. https://doi.org/10.1146/annurevcellbio-101512-122410 Beauzamy, L., Nakayama, N., & Boudaoud, A. (2014). Flowers under pressure: Ins and outs of turgor regulation in development. Annals of Botany, 114(7), 1517–1533. https://doi.org/10.1093/aob/mcu187 Benkert, R., Obermeyer, G., & Bentrup, F. W. (1997). The turgor pressure of growing lily pollen tubes. Protoplasma, 198(1–2), 1–8. https://doi.org/10.1007/BF01282125 Cosgrove, D. J. (2022). Building an extensible cell wall. Plant Physiology, 189(3), 1246–1277. https://doi.org/10.1093/plphys/kiac184 9 Haas, K. T., Wightman, R., Meyerowitz, E. M., & Peaucelle, A. (2020). Pectin homogalacturonan nanofilament expansion drives morphogenesis in plant epidermal cells. Science, 367(6481), 1003–1007. https://doi.org/10.1126/science.aaz5103 Hunt, R., Meidner, H., Grime, J. P., Hodgson, J. G., Williams, J. T., Holden, J. H. W., & Causton, D. R. (1990). PLANT DEVELOPMENT TITLES OF RELATED INTEREST Basic growth analysis Class experiments in plant physiology Comparative plant ecology Crop genetic resources Introduction to vegetation analysis Introduction to world vegetation (2nd edition) (B. M. and C. J (ed.); II). Reproduction, L., & Lyon, E. N. S. De. (2021). Endosperm turgor pressure both promotes and restricts seed growth and size Abstract : (Vol. 1). Robinson, S., Burian, A., Couturier, E., Landrein, B., Louveaux, M., Neumann, E. D., Peaucelle, A., Weber, A., & Nakayama, N. (2013). Mechanical control of morphogenesis at the shoot apex. Journal of Experimental Botany, 64(15), 4729–4744. https://doi.org/10.1093/jxb/ert199 Scott, R. J., Spielman, M., & Dickinson, H. G. (2004). Stamen structure and function. Plant Cell, 16(SUPPL.), 46–60. https://doi.org/10.1105/tpc.017012 10
