Apoplast and Symplast (2022)

The term apoplast was coined in 1930 by Munch in order to separate the living symplast from the dead apoplast. The apoplast is the space outside the plasma membrane within which material can disperse freely. It is broken up by the Casparian strip in roots, by air spaces between plant cells and by the plant cuticle. The apoplast route facilitates the transportation of water and solutes across a tissue or organ. This process is called apoplastic transport.

Symplast

The symplast is the inner side of the plasma membrane in which the water and low-molecular-weight solutes can freely diffuse. Symplast cells have more than one nucleus. The water enters the cytoplasm of the cell all the way through the plasma membrane; hence, the symplastic pathway should cross cell membranes. Since the symplastic pathway crosses the cell membrane, it is also called the transmembrane pathway. The movement of water in the symplastic pathway is assisted by cytoplasmic streaming.

The apoplast is important for all the plant’s interaction with the environment. The main carbon source, i.e. the carbon dioxide, wants to be solubilised in the apoplast before it imparts through the plasma membrane into the cytoplasm of the cell and is used by the chloroplasts during photosynthesis.

In poor nitrate soil, acidification of the apoplast increases cell wall extensibility and root growth rate. An apoplast is also a place for cell-to-cell communication.

Water Transport in Apoplast

The water enters the plant all the way through the hair on the root, which transports it up and around the plant and solutes are moved around by the xylem and the phloem, using the root, stem, and plant.

Root

Water enters the root in the course of root hairs and then one of three paths (apoplast, symplast, and vacuolar to the xylem vessel.

Root Hair to Xylem

From the root hair, water again moves by osmosis down an absorption gradient toward the xylem and can take one of the three ways-apoplast, symplast of the vacuolar.

The apoplast way is where the water takes a route going from cell wall to cell wall, not entering the cytoplasm at any point. The simplest pathway is where water moves between the cytoplasm and vacuoles of adjacent cells. The apoplast pathway can only take water a certain way, near the xylem of the Casparian strip forms a tightly packed barrier to water in the cell walls and water must shift into the cytoplasm to continue.

This gives the plant control over the ions that penetrate into its xylem vessels since water must cross a plasma membrane.

(Video) Apoplastic and Symplastic Pathways (A Level Biology)

The apoplast has recently become apparent that it plays a major role in a diverse range of processes, including plant-microbe, intercellular signalling, and both water and nutrient transport. The apoplast constitutes all chambers away from plasmalemma- the interfibrillar and internal space of the cell wall and the xylem, as well as its gas and water-filled intercellular space spreading to the rhizoplane and cuticle of the outer plant surface.

The physical and chemical properties of cell walls control plant mineral nutrition, as nutrients do not simply pass through the apoplast to the plasmalemma but can also be absorbed or fixed to cell wall components. Here, the current progress understanding of the significance of the apoplast in plant mineral nutrition is reviewed.

The contribution of the root apoplast to short-distance transport and nutrient uptakes is examined particularly in relation to sodium toxicity and aluminium tolerance. This extends to long-distance transport and the role of the apoplast as a habitat for microorganisms. In the leaf, the apoplast might have benefits over the vacuole as a site for short-term nutrient storage space and solute exchange with the atmosphere.

Apoplastic Movement Altered at the Endodermis

The endodermis is the central, innermost layer of the cortex in some land plants. It is made of compact living cells surrounded by an outer ring endodermal cells that are impregnated with hydrophobic substances, i.e. Casparian strip to restrict the apoplastic flow of water to the inner side.

The cells of the endodermis have their main cell walls thickened on the four side’s radial and sloping with suberin, the water-impermeable waxy substance which in young endodermal cells are deposited in the Casparian strips. The strips vary in width but are typically smaller than the cell wall on which they are deposited. For example, in smokestack (brick cylinder), if the endodermis is likened to the smokestack with the bricks representing individual cells, the Casparian strip is analogous to the mortar between the bricks.

Apoplast and Symplast

The root hair cells absorb water from the soil by osmosis. The water that is absorbed is transported to the xylem to the root through the root cortex. Transportation occurs by osmosis. The apoplast is the route the water moves through the cell walls and intercellular space of the root cortex. In the symplastic route, the water moves through the protoplasts of the root cortex.

The apoplast route is the fully permeable route in which the water movement occurs in passive diffusion. Whereas the symplast is a selectively permeable route in which the water movement occurs by osmosis. The endodermis prevents the water and any solutes dissolved in water from passing through this layer via the apoplast pathway. Water can also pass through the endodermis by crossing the membrane of endodermal cells twice. Water moving in and out of the xylem, which is a part of apoplast, can thereby be regulated since it must enter the symplast in the endodermis.

Apoplast and Symplast (2)

(Video) AS Biology - water pathways through a plant

The Difference Between Apoplast and Symplast

Apoplast

Symplast

Apoplast refers to the non protoplasmic components of a plant, including the cell wall and the intracellular spaces.

Symplast refers to the continuous arrangement of protoplasts of a plant, which are interconnected by plasmodesmata.

Apoplast consists of non protoplasmic parts such as cell wall and intracellular space.

Symplast Consists of protoplast

Apoplast is composed of nonliving parts of a plant.

Symplast is composed of living parts of a plant.

In apoplast, the water movement occurs by passive diffusion.

In symplast, the water movement occurs by osmosis.

In apoplast, the water movement is rapid.

In the symplast, the water movement is slower.

The metabolic rate of the cells in the root cortex does not affect the water movement.

The metabolic rate of the cells in the root cortex highly affects the water movement.

It shows less resistance to the water movement.

It shows some resistance to the water movement.

With the secondary growth of the root, most of the water moves by the apoplast route.

Beyond the cortex, water moves through the symplast route.

Similarities Between Apoplast and Symplast

  • Apoplast and symplast are two ways in which the water moves from root hair cells to the xylem.

  • Both the apoplast and symplast occur in the root cortex.

  • Both the apoplast and symplast carry water and nutrients towards the xylem.

Pathways For Root Absorption Through Apoplast

The apoplastic pathway provides a way towards the vascular cell through free spaces and cell walls of the epidermis and cortex. An additional apoplastic route that allows direct access to the xylem and phloem is along the margins of the secondary roots. The secondary root is developed from the pericycle, a cell layer just inside the endodermis. The endodermis is characterised by the Casparian strip. Apoplast was previously defined as the whole thing but the symplast, consisting of cell walls and spaces between cells in which water and solutes can move freely.

(Video) APOPLAST AND SYMPLAST PATHWAYS OF WATER TRANSPORT IN PLANTS. PLANT WATER RELATION.

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FAQs

What is difference between apoplast and symplast? ›

The symplast is the living region present between two cells which connects one cell with the other. The apoplast pathway is the path in which the water is moving between the intercellular spaces. The apoplast includes the non living spaces between the cells and the cell membranes.

What is meant by apoplast? ›

What is Apoplast? The apoplast is the space outside the plasma membrane consisting of intercellular spaces where the material diffuses freely. It does not involve protoplasm in the plant tissues but involves the non-living parts of the plant such as cell wall and intercellular spaces.

What is the symplastic pathway? ›

The symplastic pathway: It provides the movement of water from one cell to another cell by plasmodesmata. Symplast is the inner side of the plasma membrane.

Which is faster apoplast and symplast? ›

Since the apoplast pathway does not require the entry of water through the cell membrane, it is relatively faster than the symplast pathway.

What is casparian trip? ›

Casparian strips are specially modified primary carbohydrate cell walls, in which the radial parts of the cell walls are characterized by the deposition of lignin and suberin in the primary cell wall and middle lamella (Fig. 1A–H).

Can water travel through the apoplast? ›

Water can move between cells and through the cell walls and intercellular spaces in the apoplast pathway (apoplastic route) or between adjacent cytoplasms through plasmodesmata in the symplast pathway (symplastic route).

What is the difference between apoplast and symplast pathway of transport of water? ›

The apoplast route is the fully permeable route in which the water movement occurs in passive diffusion. Whereas the symplast is a selectively permeable route in which the water movement occurs by osmosis.

What is true for both apoplast and symplast? ›

An equal rate of transport.

Is apoplast pathway continuous? ›

Reason R: Apoplast is a continuous system, while symplast is completely a discontinuous system.

Is apoplast active or passive? ›

Apoplast is composed of non-living parts of a plant whereas, symplast is composed of living parts of a plant. In apoplastic movement, water movement occurs by passive diffusion whereas, in symplastic movement, water occurs by osmosis. In apoplast, there is less resistance seen to the water movement.

Does apoplast require energy? ›

It is because, Apoplastic movement occurs through non-living parts of the plant. There is little resistance to the movement of molecules in Apoplastic movement. Also, in this movement, the metabolic state of root does not affect the movement of molecules. So, there is little energy requirement.

What is Casparian strip made of? ›

In the following, it was concluded that Casparian strips are made of suberin, an aliphatic polyester that is the main component of cork (3). However, other works found evidence that Casparian strips largely consist of a lignin-like polymer (4).

Is xylem apoplast a symplast? ›

Apoplast and symplast are two routes by which the water moves from root hair cells to the xylem. Both apoplast and symplast occur in the root cortex. Both apoplast and symplast carry water and nutrients towards the xylem.

Why are Casparian strips waterproof? ›

As a result, the soil solution has to pass through… …that have within their walls Casparian strips, water-impermeable deposits of suberin that regulate water and mineral uptake by the roots. The cortex is surrounded by the dermal system consisting of a single layer of epidermal cells.

What is pericycle and Casparian strips? ›

The Casparian strip is a waterproof and water-resistant tissue. The Casparian strip helps to stop the water from entering the pericycle except through the cytoplasm of endodermal cells and is important in producing root pressure.

What causes root pressure? ›

root pressure, in plants, force that helps to drive fluids upward into the water-conducting vessels (xylem). It is primarily generated by osmotic pressure in the cells of the roots and can be demonstrated by exudation of fluid when the stem is cut off just aboveground.

What are the 3 ways of traveling through the water? ›

Methods of transportation fall into three categories: Aqueducts, which include pipelines, canals, tunnels and bridges. Container shipment, which includes transport by tank truck, tank car, and tank ship. Towing, where a tugboat is used to pull an iceberg or a large water bag along behind it.

Can water move freely in the apoplast without entering cells? ›

In apoplast pathway water moves through cell wall without crossing any membrane.So, the correct option is 'apoplast pathway'

Why is water called elixir of life? ›

it is known as the elixir of life due to its importance in the life of the living organisms. The sources of water are depleting and so there is need to save the reserves. The ways by which water can be saved are: Use the water used for washing vegetables for watering the plants.

What are the 5 types of water transport? ›

These are:
  • Bulk Carriers.
  • General Cargo Ships.
  • Container Ships.
  • Tankers.
  • Barges.
25 Jun 2018

Is phloem apoplast or symplast? ›

In type 2 species, phloem loading is apoplastic because of the symplastic isolation and depends on the activity of sugar transport proteins in the membranes, whereas in type 1 species phloem loading is symplastic through the plasmodesmata.

How does water cross the Casparian strip? ›

The Casparian strip is impervious to water so can control the transportation of water and inorganic salts between the cortex and the vascular bundle, preventing 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 the ...

Which is not transported through symplast? ›

Which of the following is not transported through the sim symplast? 1. DNA.

How does water pass the Casparian strip? ›

In both cases, water and solutes pass the Casparian strip by diffusing through an endodermal cell and are subsequently loaded into the xylem by other transporters for long-distance transport to the shoot.

Is xylem continuous? ›

Xylem forms a continuous network of channels that connects roots to the leaves through the stem and branches to transport water to the entire plant.

What is plasmodesmata in biology? ›

Plasmodesmata (Pd) are co-axial membranous channels that cross walls of adjacent plant cells, linking the cytoplasm, plasma membranes and endoplasmic reticulum (ER) of cells and allowing direct cytoplasmic cell-to-cell communication of both small molecules and macromolecules (proteins and RNA).

Is xylem an apoplast? ›

The apoplast comprises the intercellular space, the cell walls, and the xylem.

What are the 4 types of passive transport? ›

The rate of passive transport depends on the permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the membrane lipids and proteins. The four main kinds of passive transport are simple diffusion, facilitated diffusion, filtration, and/or osmosis.

Where is casparian found? ›

Casparian strips are a cellular feature found in the roots of all higher plants. They are ring-like, hydrophobic cell wall impregnations. These impregnations occur in the endodermis, an inner cell layer that surrounds the central vascular strand of roots (Figure 1).

Where is suberin found? ›

Suberin is a lipophilic macromolecule found in specialized plant cell walls, wherever insulation or protection toward the surroundings is needed. Suberized cells form the periderm, the tissue that envelops secondary stems as part of the bark, and develop as the sealing tissue after wounding or leaf abscission.

What do you mean by lignin? ›

lignin, complex oxygen-containing organic polymer that, with cellulose, forms the chief constituent of wood. It is second to cellulose as the most abundant organic material on Earth, though relatively few industrial uses other than as a fuel have been found.

Why does xylem have no cross walls? ›

Tubular shape with no cross walls which allows a continuous column of water + facilitates more rapid transport within the xylem vessels.

Is xylem permeable or impermeable? ›

Mature xylem consists of elongated dead cells, arranged end to end to form continuous vessels (tubes). Mature xylem vessels: contain no cytoplasm. are impermeable to water.

Is the phloem Symplastic? ›

It is the difference in concentrations between the mesophyll and phloem that motivates flux, not the absolute levels in the mesophyll. Since intermediary cells have numerous plasmodesmata that link them to the bundle sheath, there is an uninterrupted symplastic pathway into the phloem.

What is the difference between Tracheids and Fibres? ›

Tracheids are not fibers, as their major function is conducting water and the cell shape is not typical of a fiber, though they have relatively thick cell walls. Both fiber-tracheids and libriform fibers have emerged from tracheids in the course of evolution and the intermediate forms can be easily found.

Where is the symplast located? ›

The symplast of a plant is the inner side of a cell membrane in which water and low-molecular-weight solutes can freely diffuse. Symplast cells have more than one nucleus.

What is true for both symplast and apoplast movement? ›

An equal rate of transport.

What are the four components of xylem? ›

Xylem consists of tracheids, vessels, parenchyma, and fibers.

Are tracheids xylem or phloem? ›

Explanation: Tracheids are elongated cells that are contained within xylem tissue. Tracheids are responsible for water and mineral transport.

What is difference between xylem and phloem? ›

Xylem carries water and minerals from the roots to the leaves. Whereas, phloem carries the food prepared by the leaves to different parts of the plant.

Is osmosis a symplastic? ›

Since cell membranes are semi-permeable, the movement of the water occurs by osmosis in the symplastic pathway. However, the water that moves through the symplast does not enter the vacuole of the cell. Since the symplastic pathway crosses the cell membrane, it is also called the transmembrane pathway.

Videos

1. symplast and apoplast pathway | NMDCAT 2021
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2. Apoplast Movement In Plants
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3. Transportation in plant || symplast, apoplast || class 11th biology by 3d animations
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4. 3.1.3. Transport in plants d) Apoplast, Symplast pathways and cohesion-adhesion tension theory.
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5. video 5 Apoplastic and symplastic
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6. AS Biology - Water transport in plants (OCR A Chapter 9.2)
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