Nitrogen, magnesium, potassium and iron.
Carbon is the macronutrient.
Azotobacter is a non- symbiotic nitrogen- fixing prokaryote.
A bacteria is present in waterlogged soil under anaerobic condition. This bacteria produce methane gas which is a green- house gas.
Manganese inhibits in the translocation of calcium to the root apex and cause its deficiency and Mn competes with Mg and iron to bind with enzymes hence causing their deficiency.
An example of this association is the rod- shaped Rhizobium and several legume like sweet pea, garden pea etc. relationship.
Essential elements are the elements that are very important for plant growth. These are of two types:
Micro elements are required in very less amount to the plants. Example: Iron, Zinc. Macro elements are required in large amount to the plants. Example: calcium, magnesium etc.
Criteria of essentiality: the criteria of essentiality is not only depend on one criteria. It is depend on the several criteria given below:
Classification of essential elements based on their functions are:
No, excess of nutrients reduces the dry weight of the tissue by 10% and leads to toxicity. It inhibit uptake of other elements than required such critical condition vary from plant to plant. Symptoms of toxicity are difficult to identify. Example: excess of manganese inhibits the uptake of Ca, iron etc.
There are commonly six events occur between the starting from the coming in contact with Rhizobium to a leguminous root till nodule formation.
Event 1: Rhizobia multiply and colonize the surroundings of roots and get attached to epidermal and root hair cells.
Event 2: The root hair cells curls and bacteria enters the root hairs.
Event 3: After the entry of bacteria in the root hair an infection thread is formed which carried bacteria to the cortex of the root.
Event 4: Formation of nodule initiates in cortex.
Event 4: The bacteria are released from the thread into the cells which leads to the differentiation of specialized nitrogen fixing cells.
Event 6: Nodule formed a vascular connection with the host for the exchange of nutrients.
Importance of leghemoglobin:
Enzyme nitrogenase only work in anaerobic condition, thus leghemoglobin helps in this.
All the necessary biochemical components are present in the root nodules for Nitrogen fixation. It contains enzymes nitrogenase and pigment leghemoglobin nitrogenase is Mo- Fe protein which help in conversion of atmospheric nitrogen into ammonia. Ammonia is the first stable product of nitrogen fixation. Equation of conversion of Nitrogen into ammonia are:
The end product of biochemical events is Ammonia (NH3). Figure to show the conversion of nitrogen into Ammonia:
Fates of NH3: The ammonia is produced through the nitrogen fixation is incorporated in the amino acids as an amino group. At physiological pH NH3 group is protonated to NH4+ group is the fate of ammonia.
And, transamination occurs:
Hydroponics has been shown to be a successful technique for growing of plants where the plants are grown in mineral nutrients instead of soil. This requires the addition of mineral regularly and change of water. The initial cost of set is very high and this method need a very high level of sterilization while growing plants.
While, most of the crops are gown still in the lands because it is free of cost and minerals are already present in the soil so there is no need of adding extra mineral into it.
These plants trap insects and they feed on them to get nutrition. Thus these are known as Insectivores.
Plants tend to absorb different kinds of nutrients from soil. However, a nutrient is inessential for a plant if it is not involved in the plant’s physiology and metabolism. For example, plants growing near radioactive sites tend to accumulate radioactive metals. Similarly, gold and selenium get accumulated in plants growing near mining sites. However, this does not mean that radioactive metals, gold, or selenium are essential nutrients for the survival of these plants.
(a) True
(b) All the mineral elements present in a cell are not needed by the cell. For example, plants growing near radioactive mining sites tend to accumulate large amounts of radioactive compounds. These compounds are not essential for the plants.
(c) Nitrogen as a nutrient element is highly mobile in plants. It can be mobilised from the old and mature parts of a plant to its younger parts.
(d) True
Hydroponics is the art of growing plants in a nutrient solution in the absence of soil. Since the plant roots are exposed to a limited amount of the solution, there are chances that the concentrations of oxygen and other minerals in the plant roots would reduce. Therefore, in studies involving mineral nutrition using hydroponics, purification of water and nutrient salts is essential so as to maintain an optimum growth of the plants.
Macronutrients: They are the nutrients required by plants in large amounts. They are present in plant tissues in amounts more than 10 mmole kg–1 of dry matter. Examples include hydrogen, oxygen, and nitrogen.
Micronutrients: They are also called trace elements and are present in plant bodies in very small amounts, i.e., amounts less than 10 mmole kg– 1 of dry matter. Examples include cobalt, manganese, zinc, etc.
Beneficial nutrients: They are plant nutrients that may not be essential, but are beneficial to plants. Sodium, silicon, cobalt and selenium are beneficial to higher plants.
Toxic elements: Micronutrients are required by plants in small quantities. An excess of these nutrients may induce toxicity in plants. For example, when manganese is present in large amounts, it induces deficiencies of iron, magnesium, and calcium by interfering with their metabolism.
Essential elements: These elements are absolutely necessary for plant growth and reproduction. The requirement of these elements is specific and non-replaceable. They are further classified as macro and micro-nutrients.
The five main deficiency symptoms arising in plants are:
• Chlorosis
• Necrosis
• Inhibition of cell division
• Delayed flowering
• Stunted plant growth
Chlorosis or loss of chlorophyll leads to the yellowing of leaves. It is caused by the deficiencies of nitrogen, potassium, magnesium, sulphur, iron, manganese, zinc, and molybdenum.
Necrosis is the death of plant tissues as a result of the deficiencies of calcium, magnesium, copper, and potassium.
Inhibition of cell division is caused by the deficiencies of nitrogen, potassium, sulphur, and molybdenum.
Delayed flowering is caused by the deficiencies of nitrogen, sulphur, and molybdenum.
Stunted plant growth is a result of the deficiencies of copper and sulphur.
In plants, the deficiency of a nutrient can cause multiple symptoms. For example, the deficiency of nitrogen causes chlorosis and delayed flowering.
In a similar way, the deficiency of a nutrient can cause the same symptom as that caused by the deficiency of another nutrient. For example, necrosis is caused by the deficiency of calcium, magnesium, copper, and potassium.
Another point to be considered is that different plants respond in different ways to the deficiency of the same nutrient.
Hence, to identify the nutrient deficient in a plant, all the symptoms developed in its different parts must be studied and compared with the available standard tables.
Deficiency symptoms are morphological changes in plants, indicating nutrient deficiency. Deficiency symptoms vary from one element to another. The plant part in which a deficiency symptom occurs depends on the mobility of the deficient element in the plant. Elements such as nitrogen, potassium, and magnesium are highly mobile. These elements move from the mature organs to the younger parts of a plant. Therefore, the symptoms for the deficiencies of these elements first appear in the older parts of the plant. Elements such as calcium and sulphur are relatively immobile. These elements are not transported out of the older parts of a plant. Therefore, the symptoms for the deficiencies of these elements first appear in the younger parts of the plant.
The absorption of soil nutrients by the roots of plants occurs in two main phases – apoplast and symplast.
During the initial phase or apoplast, there is a rapid uptake of nutrients from the soil into the free spaces of plant cells. This process is passive and it usually occurs through trans-membrane proteins and ion-channels.
In the second phase or symplast, the ions are taken slowly into the inner spaces of the cells. This pathway generally involves the expenditure of energy in the form of ATP.
Rhizobium is a symbiotic bacteria present in the root nodules of leguminous plants. The basic requirements for Rhizobium to carry out nitrogen fixation are as follows:
(a) Presence of the enzyme nitrogenase
(b) Presence of leg-haemoglobin
(c) Non-haem iron protein, ferrodoxin as the electron-carrier
(d) Constant supply of ATP
(e) Mg2+ions as co-factors
Rhizobium contains the enzyme nitrogenase – a Mo-Fe protein – that helps in the conversion of atmospheric free nitrogen into ammonia.
The reaction is as follows:
N2 + 8e– + 8H+ + 16 ATP→ 2 NH3 + H2 + 16ADP + 16Pi
The Rhizobium bacteria live as aerobes under free-living conditions, but require anaerobic conditions during nitrogen fixation. This is because the enzyme nitrogenase is highly sensitive to molecular oxygen. The nodules contain leg-haemoglobin, which protects nitrogenase from oxygen.
Multiple interactions are involved in the formation of root nodules:
1) The Rhizobium bacteria divide and form colonies. These get attached to the root hairs and epidermal cells.
2) The root hairs get curled and are invaded by the bacteria.
3) This invasion is followed by the formation of an infection thread that carries the bacteria into the cortex of the root. The bacteria get modified into rod-shaped bacteroides.
4) As a result, the cells in the cortex and pericycle undergo division, leading to the formation of root nodules.
5) The nodules finally get connected with the vascular tissues of the roots for nutrient exchange.
