Turgor is the internal pressure within plant cells, created by water. This pressure pushes against the cell walls, providing plants with rigidity and shape. Without sufficient turgor, plants would lose their structural integrity.
Understanding Turgor Pressure
Turgor pressure is the force exerted by water inside a plant cell against its cell wall. Water enters the cell and accumulates in a large central vacuole, which then swells and pushes the cell’s contents, including the cell membrane, against the rigid cell wall.
When a plant cell is full of water and firm, it is described as turgid. Conversely, if a cell loses water, the pressure inside decreases, causing it to become soft or flaccid. The cell wall provides mechanical support, resisting the internal pressure and preventing the cell from bursting, while the cell membrane regulates the movement of water and dissolved substances.
The Mechanism Behind Turgor
Turgor pressure develops through a process called osmosis, which is the movement of water molecules across a semipermeable membrane. Water moves from an area where its concentration is higher (less solutes) to an area where its concentration is lower (more solutes).
In plant cells, the central vacuole contains a solution of sugars, salts, and other solutes, creating a lower water concentration inside the cell compared to the surrounding environment. This difference in concentration draws water into the cell and specifically into the vacuole. The strong and rigid cell wall, composed of cellulose, pectins, and hemicelluloses, resists this expansion.
The Importance of Turgor in Plants
Turgor provides the structural support that allows plants to maintain their upright posture, preventing them from drooping. This internal pressure helps keep stems firm and leaves extended, enabling them to capture sunlight effectively for photosynthesis. The rigidity offered by turgor is particularly evident in non-woody tissues such as young stems and leaves.
Turgor pressure plays a role in plant growth by facilitating cell expansion. The pressure helps stretch the cell walls, allowing individual cells to enlarge, which contributes to the overall growth of the plant.
Turgor also influences the transport of water and dissolved nutrients throughout the plant. It contributes to the root pressure that helps push water upwards into the xylem vessels.
Turgor changes regulate the opening and closing of stomata, which are small pores on leaf surfaces. Guard cells, which surround these pores, become turgid when water enters them, causing the stomata to open and allowing for gas exchange, including carbon dioxide intake for photosynthesis. When guard cells lose turgor, they become flaccid, and the stomata close, helping the plant conserve water.
What Happens When Turgor is Lost
When a plant does not absorb enough water, its cells lose turgor pressure. This reduction causes the plant to lose firmness and rigidity, leading to wilting. Stems become soft and droopy, and leaves lose their extended form, often hanging downwards.
If water loss continues, the cell membrane can pull away from the cell wall, a process sometimes observed as the plant’s protoplasm shrinking. While the cell wall maintains its shape, reduced internal pressure means the cell no longer presses against it. This condition often occurs when plants are in dry soil or environments with high solute concentrations that draw water out of the cells. Wilting due to turgor loss is often reversible if the plant is rehydrated promptly.