Mineral Absorption

Soil is the main sources of mineral salts. These mineral salts are mainly absorbed by the (Sub­terminal) meristematic region of the roots.

There are two methods' of absorption of mineral salts:
 

Passive Absorption of Minerals

 (Without expenditure of ATP)

1. By simple diffusion: According to this method mineral ions may diffuse in root cells from the soil solution.

2. By mass flow: According to this method mineral ions absorption occurs with flow of water under the influence of transpiration.

3. By ion exchange: This involves exchange of mineral ions with the ions of same charge.

(i) By contact exchange: When the mineral ion exchange with the H⁺ and OH^- ions.

(ii) Carbonic add exchange: When the mineral ion exchange with the ions of carbonic acid. 

4. By Donnan equilibrium: This theory explains the passive accumulation of ions against the concentration gradient or electrochemical potential (ECP) without ATP. At the inner side of cell membrane which separates from outside (external medium), there are some anions which are fixed or non diffusible and membrane is impermeable to .these anions, while cations are diffusible.

Active Ion Absorption

(By expenditure of ATPs) Evidences in favour of active mineral absorption:

1.Rate of respiration of plant is increased when plant transferred in to mineral solution. (Salt respiration)

2. Factors like deficiency of oxygen, CO, CN, which inhibit rate of respiration, these factors also inhibits the absorption of mineral ions in plants.

3. Absorption of K⁺ ions in Nitella algae is observed against the concentration gradient. 

Cytochrome pump theory: By Lundegardh Burstorm (1933) According to this theory, only anions are absorbed by active mechanism through cytochrome pumping and absorption ~f cation is passive process.

According to cytochrome pump theory respiration is called as anion respiration.

Carrier concept: By Vanden honert. According to this theory some specific carrier molecules made up of proteins are present in cell membrane of root cell which absorbs both the ions and form ion­ carrier complex. This complex is break inside the cell membrane with expenditure of energy. 

Protein-Lecithin Theory: By Bennet Clark According to this theory a phospholipid lecithin in root cell membrane works as carrier for both type of ions.

Lecithin has two type of groups 

Goldacre: A contractile protein is associated with absorption of minerals.

P.R. Stout and Hoagland (1939) proved that mineral salts are translocated through xylem along with transpiration pull (exp. with help of radioisotopes).

Factors Affecting Mineral Absorption

The process of mineral absorption is influenced by the following factors:

Temperature: The rate of absorption of salts and minerals is directly proportional to temperature. The absorption of mineral ions is inhibited when the temperature has reached its maximum limit, perhaps due to denaturation of enzymes.

Light: When there is sufficient light, more photosynthesis occurs. As a result more food energy becomes available and salt uptake increases.

Oxygen: A deficiency of 02 always causes a corresponding decrease in the rate of mineral absorption. It is probably due to unavailability of ATP. The increased oxygen tension helps in increased uptake of salts.

pH: It affects the rate of mineral absorption by regulating the availability of ions in the medium .

At normal physiological pH monovalent ions are absorbed more rapidly whereas alkaline pH favours the absorption of bivalent and trivalent ions.

Interaction with other minerals: The absorption of one type of ions is affected by other type. The absorption of K⁺ is affected by Ca⁺⁺", Mg⁺⁺ and other polyvalent ions. It is probablydue to competition for binding sites on the carrier. However, the uptake of K⁺ and Br^- becomes possible in presence of Ca⁺⁺.ions. There is mutual competition in the absorption of K, Rb and Cs ions.

Growth: A proper growth causes increase in surface area, number of cells and in the number of binding sites for the mineral ion. As a result, mineral absorption is enhanced. 

Note:

C, H, O, N, P is main constituents of protoplasm (organic materials). So they called protoplasmic elements, C, N & O from atmosphere and H₂ O from soil for H & O.

C, H, O is main components of nucleic acid, proteins, enzymes, carbohydrates, fats. (Frame work elements)

Most of soil deficient of NPK and these elements are known as critical elements, NPK -fertilizer is good for crop yield.

Co is part of Vit.-B₁₂ which acts as coenzyme, Cobalt also used in cancer therapy and g-garden of crop improvement.

Silica (SiO₂) is present in cell wall of diatoms grasses and paddy straw.

At-present in pteridophytes i.e. - Lycopodium.

Mo, require in minimum quantity.

Hydroponics/solution culture/soilless growth tank farming and ash analysis is a technique which determine the role of nutrients in plants. (By Geriack)

Gold (Au) present in Equiseium, Mustard plants.

Plants grown in moistened air with nutrients is aeroponics.

Root meristem is important in storage and absorption of minerals.

Na⁺ found in halophytes for their growth (marine plants).

Trace element are micro-nutrients while tracer­ elements are radio-isotopes.

Mg present in chlorophyll as non-ionic form (as Fe in. Hb)

Mg remains after chlorophyll burning.

Minerals and organic matter regulates the osmotic concentration of cell.

Mo in nitrogen metabolism.

One abundant and stable form of Fe in leaves is stored in chloroplasts as an iron protein complex called Phytoferritin (Seckback 1983).

C, H, O are provided by H₂O, O₂ and CO₂ but 13 elements essential to all plants are absorbed as ions from the soil solution, is called a solution mining. (N₂ from soil & atm.).

Purification/Proteolysis: Bacillus, Pseudomonas, Clostridium.

Proteins  peptides  amino  acids (conversion of proteins into- amino acids) smell of dead bodies.

Deamination: Removal of amino group as NH3 from an amino acid.

Parasites: These plants .obtain either their organic food prepared by other organisms or depend upon other plants only' for water and minerals with the help of which they can synthesize their own food. The living organism from which the parasite obtains its organic food or water and minerals is called host. Any part of the body of parasite is modified into a special organ called haustorium which enters into the cells of host and absorbs food or water and minerals from the host.

Partial stem parasites: The well known example of partial stem parasite is Viscum album (mistletoe) which parasitizes a number of shrubs and trees. The mature plant of Viscum is dichotomously branched with green leaves born in pairs attached on each node of stem. The shoots are attached to the host by means of haustoria. The primary haustoria reaches upto cortex of the host which runs logitudinally. It sends secondary haustoria which make connection with the xylem of the host and absorb water and minerals Loranthus is another partial stem parasite.

Partial root parasites: The common example of partial (semi-parasite) root parasite is Sanialum album (Sandal wood tree) which is an evergreen partial root parasite which grows in South India. It grows on the roots of Dalbergia sisso, Eucalyptus. Like other partial parasites, it also has green leaves and absorbs only minerals and water from the host plants.

Similarly, Striga on roots of sugarcane and Thesium on the roots of grasses are other partial root parasites.

Root nodules of leguminosae: Members of the sub-family Papilionaceae of the Leguminosae (e.g., pea, beans, trifolium) harbour species of Rhizobium, a nitrogen fixing bacteria. The bacteria form nodules in the roots. They fix elemental nitrogen of the atmosphere and make it available to the plant in forms that can be utilized. In turn they derive food and shelter from the leguminous plant.

Drosera (Sundew): It is a herbaceous plant having spathulateor lunate leaves. The leaves are covered by glandular hair with a swollen tip. The glands secretes a sticky purple juice which shines like a dew drop in bright light sunshine, hence the name sundew. These long special hair are generally referred to as 'tentacles'. When an insect alights on the leaf, the tentacles curve due to thigmonasty. The insect is killed and its proteins are digested by pepsin hydrochloride. Similar tentacles are also found in Drosophyllum.

Utricularia (Bladderwort): It is submerged floating aquatic herb which lacks roots. Some of the species of Utricularia also occur in moist soil. The leaves are dissected into fine segments and appear like roots. Some of the leaf segments are modified into pear-shaped sacs called bladders or utricles.

Nepenthes (Pitcher plant): They are commonly found in tropical areas like Assam and Meghalaya (i.e., N. Khasiana). In this plant the leaf base is winged, petiole is tendrillar and the lamina is modified into  pitcher. The pitcher has a distinct collar at the mouth and the apex is modified into the lid. The undersurface of the lid has alluring glands whereas the inner surface of pitcher is lined by numerous digestive glands and several downward directed hair. The lid attracts insects which slide down into the pitcher. The downward directed hair check their escape. The insect is killed and its proteins are digested by pepsin hydrochloride. Other insectivorous plants having leaf pitchers are Sarracenia, Cephalotus, Heliamphora, etc. 

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