Extracellular space, outside the cell membranes of plants
The apoplastic and symplastic pathways
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The apoplast is the extracellular space outside of plant cell membranes, especially the fluid-filled cell walls of adjacent cells where water and dissolved material can flow and diffuse freely. Fluid and material flows occurring in any extracellular space are called apoplastic flow or apoplastic transport. The apoplastic pathway is one route by which water and solutes are transported and distributed to different places through tissues and organs, contrasting with the symplastic pathway.
To prevent uncontrolled leakage to unwanted places, in certain areas there are barriers to the apoplastic flow:
in roots the Casparian strip has this function[clarification needed]
Outside the plant epidermis of aerial plant parts is a protective waxy film called plant cuticle that protects against drying out, but also waterproofs the plant against external water.
The apoplast is important for all the plant's interaction with its environment:
The main carbon source (carbon dioxide) needs to be solubilized, which happens in the apoplast, before it diffuses through the cell wall and across the plasma membrane, into the cell's inner content, the cytoplasm, where it diffuses in the symplast to the chloroplasts for photosynthesis.
In the roots, ions diffuse into the apoplast of the epidermis before diffusing into the symplast, or in some cases being taken up by specific ion channels, and being pulled by the plant's transpiration stream, which also occurs completely within the boundaries of the apoplast.[clarification needed] Similarly, all gaseous molecules emitted and received by plants such as oxygen must pass through the apoplast.
In nitrate poor soils, acidification of the apoplast increases cell wall extensibility and root growth rate. This is believed to be caused by a decrease in nitrate uptake (due to deficit in the soil medium) and supplanted with an increase in chloride uptake. H+ATPase increases the efflux of H+, thus acidifying the apoplast.[clarification needed][1]
The apoplast is a site for cell-to-cell communication. During local oxidative stress, hydrogen peroxide and superoxide anions can diffuse through the apoplast and transport a warning signal to neighbouring cells. In addition, a local alkalinization of the apoplast due to such stress can travel within minutes to the rest of the plant body via the xylem and trigger systemic acquired resistance.[2]
The apoplast also plays an important role in resistance to aluminium toxicity.
In addition to resistance to chemicals, the apoplast provides the rich environment for microorganisms endophytes which arises[??] the abiotic resistance of plants.[clarification needed][3] Exclusion of aluminium ions in[clarification needed] the apoplast prevent toxic levels which inhibit shoot growth, reducing[?] crop yields.[4]
^Skobelev, O (July 2010). "Accelerated root growth induced by nitrate deficit is related to apoplast acidification". Russian Journal of Plant Physiology. 57 (4): 489. ISSN 1021-4437.
^H. H. Felle; A. Herrmann; R. Hückelhoven; K.-H. Kogel (December 2005). "Root-to-shoot signalling: apoplastic alkalinization, a general stress response and defence factor in barley (Hordeum vulgare)". Protoplasma. 227 (1): 17–24. doi:10.1007/s00709-005-0131-5. PMID 16389490. S2CID 5017915.
^Sattelmacher, Burkhard (February 2001). "The apoplast and its significance for plant mineral nutrition". New Phytologist. 149 (2): 167–192. doi:10.1046/j.1469-8137.2001.00034.x. ISSN 0028-646X. PMID 33874640. S2CID 86799768.
^Horst, Walter J. (1995). "The role of the apoplast in aluminium toxicity and resistance of higher plants: A review". Zeitschrift für Pflanzenernährung und Bodenkunde. 158 (5): 419–428. doi:10.1002/jpln.19951580503.
The apoplast is the extracellular space outside of plant cell membranes, especially the fluid-filled cell walls of adjacent cells where water and dissolved...
gradient that allows the compound to traverse the plants' apoplast. Once free in the apoplast, gaseous ammonia is absorbed into metabolic cells by the...
sucrose is unloaded from the phloem into the apoplast. The increased sugar concentration in the apoplast decreases the water potential and triggers the...
endodermal cell walls. Water and ions move in these cell walls via the apoplast pathway. Ions outside the endodermis must be actively transported across...
solutes dissolved in the water, from passing through this layer via the apoplast pathway. Water can only pass through the endodermis by crossing the membrane...
membranes, within which water and solutes can diffuse freely. By contrast the apoplast is any fluid-filled space within the cell wall and extracellular space...
cytoplasm; a feature that enables the proper function of the exodermis. The apoplast is located outside the plasma membrane of the root cells and is the location...
water and inorganic salts from being transported to the stele through the apoplast, so that it must enter the cell membrane and move to the stele through...
transported via the xylem to the leaves where it evaporates into the air/apoplast-interface of the substomatal cavity. It is driven by capillary action and...
(1994). "A Nitrogen-Fixing Endophyte of Sugarcane Stems (A New Role for the Apoplast)". Plant Physiology. 105 (4): 1139–1147. doi:10.1104/pp.105.4.1139. PMC 159442...
theory by Julius Wiesner (1886). In 1930, Ernst Münch coined the term apoplast in order to separate the "living" symplast from the "dead" plant region...
the plant, which increases the osmotic gradient between the symplast and apoplast of these plant cells. Water then enters the cells along its osmotic gradient...
two cells surrounding the stoma which control gas exchange between the apoplast of the plant and the external environment. guttate Having droplet-shaped...
development of the seed. One example of this is maintaining a low pH in the apoplast. In cereals, the aleurone layer releases organic and phosphoric acids in...
Retrieved 28 February 2020. Horst, Walter J. (1995). "The role of the apoplast in aluminium toxicity and resistance of higher plants: A review". Zeitschrift...
water-soluble and less toxic. Once transported through the cell membrane to the apoplast, the glucose is removed, and the polymerisation commences. Much about its...
intervening middle lamella, forming an extracellular domain known as the apoplast. Although cell walls are permeable to small soluble proteins and other...
establishes an electrochemical of H+ ions from inside the cell to the apoplast, which in turn creates an osmotic gradient. This leads to loss of turgor...
and nutrients taken up by the root from entering the stele through the apoplast. Instead, water must bypass the endodermis via the symplast. This allows...
activity. Secondary metabolites are often deposited as crystals in the apoplast. Secondary metabolites are thought to play a role in preference for some...
including the nucleus, mitochondria, endoplasmic reticulum (ER), chloroplast, apoplast, peroxisome and plasma membrane. Some target peptides are cleaved from...
activation of plant defense reactions and the precipitation of silica in the apoplast of the plant. Dissolved silica (DSi) is a term used in the field of oceanography...
result little flow usually occurs making this pathway insignificant, the Apoplast pathway and Symplast pathway being the major pathways for movement of water...
solutes traveling through the phloem can move either as a symplast, or apoplast. The loading and unloading of phloem sap is done mainly by pressure flow...
considered a secondary substance and high proton concentration in the apoplast powers the inward movement of certain ions by symporters. A Proton gradient...
Shrestha, Pradeep M. (2014). "Solute accumulation differs in the vacuoles and apoplast of ripening grape berries". Planta. 239 (3): 633–642. doi:10.1007/s00425-013-2004-z...
interfaces: 1) the soil-fungus interface, 2) the fungus-apoplast interface, and 3) the apoplast-root cell interface. It has been estimated that ectomycorrhizal...
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