How do nutrients enter plants

This band is similar to a sleeve and is located inside several cell layers from the outside cell surface. This could be envisioned as wearing an outside wool sweater with an inside jacket protecting one from the wind.

The inside jacket would be similar to the casparian strip. The corky deposit surrounds the cell, as does the cement mortar around a brick, but it does not cover the front or the back of the cells. The plant root cells embedded within the casparian strip force all nutrient ions to enter directly through these living cells.

The nutrient ions must move from the outside to the inside of the root. Thus, if the roots were penetrated, a net flow of nutrients would leak from the plant roots. However, this does not occur. The corky deposit prevents leakage.

To push nutrients into the root in the face of higher nutrient concentration inside, the plant cells must exert energy. This energy comes from ATP adenosine triphosphate , the energy molecule of all cells.

Some theories explain the facts we do know. Apparently, the plant cells contain in their cell walls a special molecule called a carrier with the ability to recognize each specific nutrient ion. Thus, the cell comprises a variety of these special carrier molecules, with one for each different nutrient. For example, separate carriers exist for calcium, magnesium, copper and zinc. Some of the water and the nutrients contained in this water moves below the root zone.

This process is referred to as leaching. Many of the concerns about environmental quality revolve around leaching. By monitoring nutrients in water in tile lines and water moving through sandy soils, the Discovery Farms-Minnesota initiative is measuring the amount of water and, especially nitrogen, that moves below the root zone. The quantity of these three nutrients that reach the root surface via mass flow is not a constant value.

There are several management practices that affect water use by plants as well as the amount of nitrate, sulfate, and borate in this water. Diffusion For the essential nutrients that have a positive electrical charge when dissolved in the soil water, the major mechanism of nutrient movement to the root surface is the very slow process of diffusion.

These positively charged nutrients are associated with the clay component of the soil aggregates. Using a chemistry definition, diffusion is the movement of a nutrient ion from an area of high concentration to an area of lower concentration. In soil system, the surface of the root is usually considered to be the area of lower concentration.

The surface of the clays in the soil aggregates is thought to be the area of high concentration. Thus, plant species utilize various strategies for mobilization and uptake of nutrients as well as chelation, transport between the various cells and organs of the plant and storage to achieve whole-plant nutrient homeostasis.

Here, we briefly describe a few examples of strategies used by plants to acquire nutrients from the soil. Potassium K is considered a macronutrient for plants and is the most abundant cation within plant cells. Potassium deficiency occurs frequently in plants grown on sandy soils resulting in a number of symptoms including browning of leaves, curling of leaf tips and yellowing chlorosis of leaves, as well as reduced growth and fertility.

Potassium uptake processes have been the subject of intense study for several decades. Early studies indicated that plants utilize both high and low affinity transport systems to directly acquire potassium from the soil.

Low affinity transport systems generally function when potassium levels in the soil are adequate for plant growth and development. The expression of these low affinity transporters does not appear to be significantly affected by potassium availability.

There are likely many proteins involved in high affinity potassium transport, but in Arabidopsis, two proteins have been identified as the most important transporters in this process. More recent work shows that plants contain a number of different transport systems to acquire potassium from the soil and distribute it within the plants. Although much remains to be learned about potassium uptake and translocation in plants, it is clear that the mechanisms involved are complex and tightly controlled to allow the plant to acquire sufficient amounts of potassium from the soil under varying conditions.

Iron is essential for plant growth and development and is required as a cofactor for proteins that are involved in a number of important metabolic processes including photosynthesis and respiration.

Iron-deficient plants often display interveinal chlorosis, in which the veins of the leaf remain green while the areas between the veins are yellow Figure 2. Due to the limited solubility of iron in many soils, plants often must first mobilize iron in the rhizosphere a region of the soil that surrounds, and is influenced by, the roots before transporting it into the plant.

Figure 2: Iron-deficiency chlorosis in soybean. The plant on the left is iron-deficient while the plant on the right is iron-sufficient. All rights reserved. Strategy I is used by all plants except the grasses Figure 3A.

It is characterized by three major enzymatic activities that are induced in response to iron limitation and that are located at the plasma membrane of cells in the outer layer of the root. Second, strategy I plants induce the activity of a plasma-membrane-bound ferric chelate reductase. Finally, plants induce the activity of a ferrous iron transporter that moves ferrous iron across the plasma membrane and into the plant. In contrast, the grasses utilize strategy II to acquire iron under conditions of iron limitation Figure 3B.

Following the imposition of iron limitation, strategy II species begin to synthesize special molecules called phytosiderophores PSs that display high affinity for ferric iron. PSs are secreted into the rhizosphere where they bind tightly to ferric iron. Interestingly, while both strategies are relatively effective at allowing plants to acquire iron from the soil, the strategy II response is thought to be more efficient because grass species tend to grow better in calcareous soils which have a high pH and thus have limited iron available for uptake by plants.

Strategy I plants induce the activity of a proton ATPase, a ferric chelate reductase, and a ferrous iron transporter when faced with iron limitation. In contrast,Strategy II plants synthesize and secrete phytosiderophores PS into the soil in in response to iron deficiency.

Figure 4: Nodulation of legumes. Process of root cell colonization by rhizobacteria. Nodule formed by nitrogen fixing bacteria on a root of a pea plant genus Pisum. Beyer P. Golden Rice and "Golden" crops for human nutrition. New Biotechnology 27 , Britto, D. Cellular mechanisms of potassium transport in plants. Physiologia Plantarum , Connolly, E. Time to pump iron: iron-deficiency-signaling mechanisms of higher plants.

Current Opinion in Plant Biology 11 , Ferguson B. Journal of Integrative Plant Biology 52 , Graham L. Plant Biology. Guerinot M. Plant Physiology , Hell R. Plant concepts for mineral acquisition and allocation. Current Opinion in Biotechnology 12 , While plants have ready access to carbon carbon dioxide and water except in dry climates or during drought , they msut extract minerals and ions from the soil.

Many plants have evolved mutualistic relationships with microorganisms, such as specific species of bacteria and fungi, to enhance their ability to acquire nitrogen and other nutrients from the soil.

This relationship improves the nutrition of both the plant and the microbe. Plants are able to utilize nitrogen from nitrogen-fixing bacteria or from nitrogen releaed by decomposers such as fungi.

Nitrogen is an important macronutrient because it is part of nucleic acids and proteins. Atmospheric nitrogen, which is the diatomic molecule N 2, or dinitrogen, is the largest pool of nitrogen in terrestrial ecosystems. However, plants cannot take advantage of this nitrogen because they do not have the necessary enzymes to convert it into biologically useful forms.

Biological nitrogen fixation BNF is the conversion of atmospheric nitrogen N 2 into ammonia NH 3 , exclusively carried out by prokaryotes such as soil bacteria or cyanobacteria. Biological processes contribute 65 percent of the nitrogen used in agriculture. The most important source of BNF is the symbiotic and mutualistic interaction between soil bacteria and legume plants, including many crops important to humans.

The NH 3 resulting from fixation can be transported into plant tissue and incorporated into amino acids, which are then made into plant proteins. Some legume seeds, such as soybeans and peanuts, contain high levels of protein, and serve among the most important agricultural sources of protein in the world. Specific soil bacteria called rhizobia can symbiotically interact with legume roots to form specialized structures called nodules , in which nitrogen fixation takes place.

This process entails the reduction of atmospheric nitrogen to ammonia, by means of the enzyme nitrogenase. Through symbiotic nitrogen fixation, the plant benefits from using an endless source of nitrogen from the atmosphere.

The process simultaneously contributes to soil fertility because the plant root system leaves behind some of the biologically available nitrogen.

As in any symbiotic mutualism , both organisms benefit from the interaction: the plant obtains ammonia, and bacteria obtain carbon compounds generated through photosynthesis, as well as a protected niche in which to grow. Soybean roots contain a nitrogen-fixing nodules. The bacteria are encased in b vesicles inside the cell, as can be seen in this transmission electron micrograph. A nutrient depletion zone can develop when there is rapid soil solution uptake, low nutrient concentration, low diffusion rate, or low soil moisture.

These conditions are very common; therefore, most plants rely on fungi to facilitate the uptake of minerals from the soil.