MINERAL NUTRITION IN PLANT
In plants, the source of inorganic requirements are minerals obtained directly or indirectly from the soil. These elements are known as mineral nutrients and the nutrition is called mineral nutrition. Nitrogen is also included in the mineral nutrients because it is normally obtained by the plant from soil whereas it is not a mineral element.
ROLE OF SOME IMPORTANT MINERAL NUTRIENTS AND THEIR DEFICIENCY SYMPTOMS:
Analysis of plant shows the presence of a large number of mineral elements. The amount and number of elements present in plant may also differ from plant to plant, place to place and medium to medium in which the plant grows. Some important mineral nutrients which are required in large quantities (macronutrients) are as follows.
i) Nitrogen (N):
It is found in the soil in the form of nitrates or ammonium salts.
It is an essential constituent of proteins, nucleotides, nucleic acids and many other organic molecules like chlorophyll, so the biosynthesis of these molecules require nitrogen.
NITROGEN DEFICIENCY SYMPTOMS:
Absence or low supply of nitrogen develops the following symptoms.
1. Leaves turn pale yellow due to loss in chlorophyll content called chlorosis.
2. Process of cell-division and cell enlargement are inhibited.
3. Rate of respiration is affected.
4. In certain plants veins turn purple or red due to the development of
Anthocyanin pigment e.g. tomato and apple leaves.
5. Plant growth remains stunted and lateral buds remain dormant as a result
cereals do not show characteristic tillering.
6. Prolonged dormancy and early senescence including leaf falls.
ii) Phosphorous (P):
Plants absorb phosphorous in the form of soluble phosphates such as H3PO4 and HPO4.
It is present abundantly in the growing and storage organs such as fruits and seeds.
It promotes healthy root growth and fruit ripening by helping translocation of carbohydrates.
It is an essential element involved in the formation of cell-membrane as phospholipids, nucleic acid, co-enzyme (NAD and NADP) and organic molecules such as ATP and other phosphorylated products. It plays an important role in the energy transfer reaction in oxidation-reduction processes.
Phosphorous Deficiency symptoms:
In the case of phosphorous deficiency a few symptoms resemble that of nitrogen deficiency, like premature leaf fall and development of purple red anthocyanin pigment. Deficiency of phosphorous also shows some other symptoms.
1. Cambial activity is checked.
2. Tillering of crop plant is reduced.
3. Dormancy is prolonged.
4. Growth is retarded and dead necrotic patches appear on leaves, petioles and fruits.
5. Variable colours develop e.g. plate green in Pisum, olive green in Phaseolus.
6. Causes accumulation of carbohydrates.
7. Thickening of tracheal cells are reduced and phloem differentiation becomes incomplete.
iii) Potassium (K):
Potassium is widely distributed in soil minerals. It is strongly fixed in soil, therefore, found in less available form. Exchangeable potassium appears to be readily available to the plants. The best known function of potassium is its role in stomatal opening and closing. It is found in highest concentration in the meristematic regions of plant. It is an essential activator for enzymes involved in the synthesis of certain peptide bonds and carbohydrate metabolism.
Deficiency symptoms:
The deficiency symptoms vary with the extent of the shortage of the element. In acute deficiency:
1. The colourof leaf may turn into dull or bluish green.
2. An irregular chlorosis occurs first, which is followed by the development of necrotic areas of the tip and margin of the leaf.
3 Plant is stunted in growth with a pronounced shortening of internodes and reduced production of grains.
4. Lamina of broad leaved plants curl backward towards the under surface or roll forward towards the upper surface parallel with midrib.
iv) Magnesium (Mg):
Magnesium is present in the soil in water-soluble, exchangeable and fixed form and is present in primary minerals. It is found as carbonates similar to that of calcium and held in soil as exchangeable base. It is a constituent of chlorophyll and therefore essential for the formation of green pigment. It acts as phosphorous carrier in plant, particularly in connection with the formation of seeds of high oil contents which contains compound lecithin. It is readily mobile and when its deficiency occurs, it is apparently transferred from older to young tissues where it can be re-utilized in growth processes. Magnesium is essential for the synthesis of fats and metabolisms of carbohydrates and phosphorous.
Deficiency symptoms:
1. Deficiency symptoms develop first on the older leaves and then proceed systematically towards younger leaves.
2. Chlorosis occurs.
3. Severely affected leaves may wither and shed or absciss without the withering stage. Defoliation may be quite severe.
4. Leaves, sometimes, develop necrotic spots.
Parasitic plants:
For obtaining their food requirements parasitic plants develop haustoria, which
penetrate into host tissues for absorbing nutrients requirements.
Parasitic angiosperm
Parasitic angiosperms are broadly classified into:
i) Partial stem parasite.
ii) Total stem parasite.
iii) Partial root parasite.
iv) Total root parasite.
i) Partial stem parasite:
Loranthus
Loranthus is a partial stem parasite. It has well developed thick green leaves, a somewhat woody stem and elaborated haustorialsystem. It can manufacture some of its food with the help of nutrients and water absorbed from the host plants through haustoria. The seeds get stuck up to the stem of the host plant and germinate, sending its haustoriain the tissue of the host. Loranthusis commonly found on shrubs, roseaceoustrees, Bauhinia and mango, often causes serious damage.
Viscum— produce haustorialbranches for an internal sucking system.
Cassytha filiformis — found in tropics, a leaf less, wiry stem, send the haustoriathat penetrate in the stem to develop connection with vascular tissue of host plants.
Total stem parasite:
The plants like Cuscuta(Amer-bail) is a common
parasite which attacks stems of many herbs, shrubs and trees. They send haustoria inside the tissue of host. The xylem of parasite comes in contact with the xylem of host and phloem of parasite to phloem of host. Through xylem it sucks the water and nutrients and through phloem prepared organic food material. The host plant eventually dies off due to exhaustion.
iii) Partial root parasites:
The example or types of this category are rare.
The sandal wood tree is an important example. Its seedling can grow for a year but not so independently. Within a year the sucking roots of plant attack the root of neighbouringtrees and from them nutrients are absorbed.
iv) Total root parasite:
They suck their nutritional requirements from the roots of host e.g. Orobanche, attacks the roots of plants belonging to the families Cruciferaeand Solanaceae. Cistancheparasitizes on the roots of Calatropis. Strigais found as parasite on the roots of sugarcane, commonly found on Sorghum or Jowarcrop.
Saprophyte:
Plants which break up complex dead organic food material into simple compound
and use them for their growth and development are saprophytes. There are some
examples found among flowering plants like Neotia(bird's nest or orchid)and
Monotrapa(Indian pipe), in these cases the roots of the plant form a mycorrhizalassociation with fungal mycelium to help in the absorption process.
Carnivorous plants (Insectivorous plants):
There are plants which have insects and small birds as their prey. J.D.Hooker
suggested that the digestion of carnivorous plants is like that of animals. Infact
enzymes secreted by these plants are similar to those found in human stomach
e.g. Pepsin.
i) Pitcher plant:
It has a modified leaf of pitcher shape. Common example
are Nepenthes, Sarracenia, Cephalotus, Heliamphora, Dorlingtonia. Common
pitcher plant is Sarracenia pupureaor yellow pitcher plant Sarracenia flava.
ii) Drosera intermedia or Sundew:
A plant with loose and about half a
dozen prostrate radiating leaves. The tiny leaves bear hair like tentacles with
glands at its tip. The insect, attracted by plant odour, are traped.
iii) Dionaea muscipula or Venus fly trap: It is most well known of all
carnivorous plants. Charles Darwin called it "the most wonderful plant in the world". It has a rosette of prostrate radiating leaves with the inflorescence in the centre. The junction of petiole and lamina is constricted uptothe mid-rib, the petiole is merged and lamina has two halves, with mid-rib in centre. Each half has 12-20 teeth. The teeth of one half can interlock with the teeth of the other half. In the centre of the dorsal surface of lamina are numerous secretory glands, three hairs projecting outwards which are sensitive to touch.
iv) Aldrovanda (water fly trap):
A rootless aquatic plant with floating stem. It has rosettes of modified leaves, which have two lobed mobile lamina having teeth at the margin and sensitive jointed hairs and stalked gland on the surface.
v) Utricularia or Bladder Wort:
Rootless plant have much branched slender stem Leaves are also much divided, some of the leaflets are developed into bladder like traps of about 1/16to 1/8 Inches in diameter. The trapes have trapdoor enterances which allow small aquatic animals to get in with no return.
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