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= Turgor Loss Point =



The bulk leaf turgor loss point ($$\pi_{tlp}$$) is a key measurement in plant physiology; it is the water potential (measured in MPa) of the leaf at the wilting point. At this point, the plant cells lose turgidity, and the plant is no longer able to carry out normal metabolic functions such as photosynthesis (because the stomata close) and growth (because cells need turgor pressure in order to grow). The turgor loss point varies across plant species, and having a lower turgor loss point may be an indication of drought tolerance, because it means that a plant is able to maintain normal function under more stressful conditions.

Equation
Turgor loss point can be calculated using the following equation:

$$\pi_{tlp} = {{\pi_o\varepsilon}\over{\pi_o+\varepsilon}}$$

Where $$\pi_o$$is the osmotic potential of the leaf at full turgor (the solute concentration in the leaf cells when the leaf is fully hydrated), and $$\varepsilon$$ is the modulus of elasticity of the leaf tissue.

$$\pi_o$$is the primary contributor to turgor loss point, and plants can lower the turgor loss point when they are under drought stress by osmotic adjustment in the leaves ($$\pi_o$$). Individuals or species with a lower $$\pi_o$$ are likely to be more drought tolerant, and a plant may decrease $$\pi_o$$ when under water stress by accumulating solutes. Osmotic adjustment has been shown to allow cells to continue to grow, the stomata to stay open, and photosynthesis to continue.