Transpiration stream
Encyclopedia
In plants, the transpiration stream is the uninterrupted stream of water, and other, which is taken up by the roots and, via the xylem
vessels, transported to the leaves where it will eventually evaporate into the air/apoplast
-interface of the substomatal cavity
. It is driven in by capillary action
and in some plants root pressure
. The main driving factor is the difference in water potential
between the soil and the substomatal cavity caused by transpiration
.
Transpiration =
Transpiration can be regulated through stomatal closure or opening causing water to move out and evaporate on the leaf
, while air flows in. It allows for plants to efficiently transport water up to their highest body organs, regulate the temperature of stem and leaves during heat-generating photosynthesis and it allows for upstream signaling such as the dispersal of an apoplastic alkalinization during local oxidative stress
.
A very quick summary of this is:
Osmosis =
The water passes from the soil to the root by osmosis. This is helped by the root hairs’ shape – as they are long and thin, they maximise the surface area, meaning that more water can enter into the root hairs than if their surface area were smaller. There is greater water potential in the soil than in the cytoplasm of the root hair cells. As the cells surface membrane of the root hair cell is semi – permeable, osmosis can take place; and water passes from the soil to the root hairs.
The next stage in the transpiration stream is water passing to the xylem vessels. The water either goes through the cortex cells (between the root cells and the xylem vessels) or it bypasses them – going through their cell walls.
After this, the water moves up the xylem vessels to the leaves through diffusion
: A pressure change between the top and bottom of the vessel. Diffusion takes place because there is a concentration gradient between water in the xylem vessel and the leaf (as water is transpiring out of the leaf). This means that water diffuses up the leaf. There is also a pressure change between the top and bottom of the xylem vessels, due to water loss from the leaves. This reduces the pressure of water at the top of the vessels. This means water moves up the vessels.
The last stage in the transpiration stream is the water moving into the leaves, and then the actual transpiration. First, the water moves into the mesophyll cells from the top of the xylem vessels. Then the water evaporates out of the cells into the spaces between the cells in the leaf. After this, the water leaves the leaf (and the whole plant) by diffusion through stomata.
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
vessels, transported to the leaves where it will eventually evaporate into the air/apoplast
Apoplast
Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant....
-interface of the substomatal cavity
Substomatal cavity
In plants, the substomatal cavity is the cavity located immediately proximal to the stoma. It acts as a diffusion chamber connected with intercellular air spaces and allows rapid diffusion of carbon dioxide and other gases in and out of plant cells.-References:Graham LE, Graham JM, Wilcox LW ...
. It is driven in by capillary action
Capillary action
Capillary action, or capilarity, is the ability of a liquid to flow against gravity where liquid spontanously rise in a narrow space such as between the hair of a paint-brush, in a thin tube, or in porous material such as paper or in some non-porous material such as liquified carbon fiber, or in a...
and in some plants root pressure
Root pressure
Root pressure is when roots of two different plants collide. They put pressure against eachother and the two plants form to make one. This is how new plants are created. Root pressure occurs in the xylem of some vascular plants when the soil moisture level is high either at night or when...
. The main driving factor is the difference in water potential
Water potential
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects such as surface tension...
between the soil and the substomatal cavity caused by transpiration
Transpiration
Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants , especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants...
.
Transpiration =
Transpiration can be regulated through stomatal closure or opening causing water to move out and evaporate on the leaf
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
, while air flows in. It allows for plants to efficiently transport water up to their highest body organs, regulate the temperature of stem and leaves during heat-generating photosynthesis and it allows for upstream signaling such as the dispersal of an apoplastic alkalinization during local oxidative stress
Oxidative stress
Oxidative stress represents an imbalance between the production and manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage...
.
A very quick summary of this is:
- SoilSoilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
- RootRootIn vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s and Root Hair - XylemXylemXylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
- LeavesLeaves-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...
- Air
Osmosis =
The water passes from the soil to the root by osmosis. This is helped by the root hairs’ shape – as they are long and thin, they maximise the surface area, meaning that more water can enter into the root hairs than if their surface area were smaller. There is greater water potential in the soil than in the cytoplasm of the root hair cells. As the cells surface membrane of the root hair cell is semi – permeable, osmosis can take place; and water passes from the soil to the root hairs.
The next stage in the transpiration stream is water passing to the xylem vessels. The water either goes through the cortex cells (between the root cells and the xylem vessels) or it bypasses them – going through their cell walls.
After this, the water moves up the xylem vessels to the leaves through diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
: A pressure change between the top and bottom of the vessel. Diffusion takes place because there is a concentration gradient between water in the xylem vessel and the leaf (as water is transpiring out of the leaf). This means that water diffuses up the leaf. There is also a pressure change between the top and bottom of the xylem vessels, due to water loss from the leaves. This reduces the pressure of water at the top of the vessels. This means water moves up the vessels.
The last stage in the transpiration stream is the water moving into the leaves, and then the actual transpiration. First, the water moves into the mesophyll cells from the top of the xylem vessels. Then the water evaporates out of the cells into the spaces between the cells in the leaf. After this, the water leaves the leaf (and the whole plant) by diffusion through stomata.