It is essential for a plant to survive that nutrients are absorbed by the roots and supplied to the leaves, shoots and fruits. But how exactly can the nutrients be transported within the plant to where they are needed? First, there is short-distance transport from the root surface into the root to the central cylinder, i.e. the middle of the root, from where the nutrients then reach the individual parts of the plant. This is done by long-distance transport. In this article, we explain exactly how this works.
How do nutrients get to the roots?
Short-distance transport from the root surface to the interior of the root, the central cylinder, can occur via two transport pathways. In both pathways, the nutrient supply is actively controlled by transport proteins.
What is the symplastic transport pathway?
Symplastic nutrient transport describes the transport from cell to cell via plasmodesmata, which are small tunnels of cytoplasm that connect cell walls. This occurs because the osmotic value increases from the rhizodermis to the endodermis. The transport can be regulated .
What is the apoplastic transport pathway?
Apoplastic nutrient transport occurs through water-filled transport pathways to the endodermis. Water and the nutrients dissolved in it penetrate the network of cell walls , where they are absorbed . The transport cannot be regulated.
When is which transport route into the root used?
If there are not many nutrients available for the plant, the symplastic route is preferred. This allows the roots to be supplied with nitrogen first. If there are large amounts of nutrients in the soil and the roots are therefore well supplied, apoplastic transport is used, as this allows nutrients to reach the shoots and leaves more quickly.
How do the nutrients get into the plant parts?
When the nutrients have reached the central cylinder of the plant, long-distance transport begins to the shoots, leaves and other above-ground parts of the plant such as flowers or fruits. This can take place via the phloem or xylem. These are conductive tissues that run through all plant organs and thus represent the paths within the plant. The long-distance transport of water and the minerals dissolved in it is not an active process, but is based on adhesion and cohesion.
What is xylem?
The xylem is a woody conductive tissue that primarily transports water and dissolved nutrients. Transport only occurs from the roots up to the shoots, leaves and other above-ground plant parts. The xylem is also involved in long-distance signaling in response to pathogens or environmental stress. The xylem sap contains proteins including metabolic enzymes, stress-related proteins and signal transduction proteins. Drivers of xylem transport are osmotic pressure, capillarity in the xylem vessels and transpiration.
What is phloem?
The phloem is living tissue, also known as the sieve part. It mainly transports organic substances such as sugar from the place of absorption to the place of use and storage. In photosynthesis, for example, from the leaf to the root. It consists of so-called sieve tubes, which, together with companion cells, connect the phloem with the surrounding tissue . This is how the organic substances get into the parts of the plant.
What are mobile and immobile nutrients?
Mobile nutrients are nutrients that are mobile in the phloem and xylem and can therefore be transported from one organ of the plant to another as needed. These include nitrogen (N), phosphorus (P), potassium (K), chlorine (Cl) and magnesium (Mg). If there is a deficiency in these nutrients, the older leaves will first show symptoms, such as yellow leaves, as the nutrients are transported from the older to the younger ones when the soil no longer provides enough.
Partially mobile or immobile nutrients are only mobile in the xylem, meaning they cannot be transported to other areas within the plant when needed. These include zinc (Z), molybdenum (Mo), manganese (Mn), calcium (Ca), sulphur (S), iron (Fe), boron (B) and copper (Cu) . If there is a deficiency in these nutrients, the deficiency symptoms are first seen on the young leaves. You can find out more interesting facts about nutrients in this video!
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