Plant Physiology

Plant Hormones: Definition, Characteristics, Types, Discovery, Distribution, Biosynthesis, Transport, Mechanism of Action, and Functions

The term “Phytohormones” also refers to Plant hormones. Phytohormones are organic compounds made by higher plants naturally that control growth or other physiological processes at a location far from the origin of synthesis and are only active in very small amounts. Because these hormones are produced in plants, Thimmann (1948) proposed the term “Phytohormone.” Among the hormones produced by plants are Auxins, Gibberellins, Cytokinins, Ethylene, Growth inhibitors, and Growth retardants. The first hormones found in plants were Auxins, followed by the discoveries of Gibberellins and Cytokinins.
1. The word hormone is Greek in origin and means to set in action. Cellular division, growth, and gene expression are all affected by plant hormones.
2. they are naturally produced within plants. Although fungi and bacteria also create very similar compounds that can impact plant growth,
3. Plant hormones are chemicals, not nutrients, that, in little doses, encourage and impact the growth, development, and differentiation of cells and tissues.

Types of Plant Hormones
It is generally agreed that there are five main categories of plant hormones, some of which can have a wide range of chemical compositions from one plant to the next.
The five main categories are:
a) Auxin
b) Gibberellin
c) Cytokinin
d) Ethylene
e) Absisic acid

Mineral Nutrition: Question and Answers for Class 11th  biology Chapter 12  (CBSE/ NCERT)

Toxic Elements: The micronutrients are always needed in smaller amounts, and any small reduction in their amount might cause deficiency symptoms, while an increase in their amount can cause toxicity. Toxicity can result from any reduction in mineral ion concentration that results in tissues losing 10% of their dry weight. Although the degree of toxicity differs amongst plants, it is also difficult to identify. The majority of mineral toxicity prevents other minerals from being absorbed. Example: Chlorosis is brought on by a nitrogen deficiency.
Essential Elements: The substance that must be consumed since the body cannot produce enough of it to meet all of its demands.
They are used
(a) as parts of chemical compounds in plants that relate to energy, such as magnesium and phosphorus.
(b) Enzyme activators or inhibitors, such as magnesium and zinc.
(c) For controlling osmotic potential, such as potassium.

Nitrogen Metabolism: Definition, Abiological Nitrogen Fixation, Symbiotic Nitrogen Fixation, Ammonification, Denitrification, Nitrate Assimilation, and, Formulation of Amino Acids

Formulation of Amino Acids
Reductive Ammination: In this process, glutamic acid is produced when ammonia interacts with -ketoglutaric acid.
Catalytic Amidation: Ammonia and the amino acid glutamate combine to create amide glutamine in the presence of the enzyme synthestase and ATP. In the presence of decreased coenzyme, glutamine and -ketoglutarate combine to generate two molecules of glutamate.
Transamination is when an amino group from one amino acid is transferred to the keto group of an organic acid. The primary amino acid from which the other 17 amino acids are generated through transamination is glutamic. The transaminase enzyme is in charge of such a process.

Passive Absorption: Definition, Mass Flow Hypothesis, Ion Exchange Theory, and, Facilitated Diffusion

Minerals can be absorbed by physical processes called Passive absorption, which does not directly require metabolic activity. The concept of passive absorption is based on “outer space,” also known as “free space” or “diffusion space.” Ions will freely enter or exit the tissue if just a fraction of the tissue volume is accessible to free diffusion. After some time, the portion of the tissue that is experiencing free diffusion will achieve equilibrium with the external solution, resulting in the same ion concentration within the tissue as that of the exterior solution. The term “free space” or “outside space” refers to the region of a cell or tissue that permits ion diffusion freely. Usually, only 5% of the entire root volume is accessible for free space in the root tissue. For a particular volume of open space, the amount of solute flux depends on several variables, including the rate of transpiration, the solute concentration, and the production of root hair. Cortex cells can, however, directly take up solutes from the external solution to the existence of such a free area. Due to the presence of polygalacturonic acid [carboxylic groups (R. CHOO)] in the middle lamella, the cell walls have a negative charge. The apoplasm’s negative charges function as cation exchangers, causing cations to accumulate while repelling anions. As a result, charged solute access into the free space is limited. To define “free space,” Hope and Stevens (1952) used the term apparent free space (AFS). Water-free space (WFS), a component of AFS, is open to ions and both charged and uncharged molecules. Another term for the region where anion repulsion and cation exchange occur is Donnan free space (DFS).

Active Absorption: Primary Active Transport, Pumps, Secondary Active Transport, Symport, Antiport, and Cytochrome Pump

Cytochrome Pump
This theory was put forth by H. Lundegardh in 1954 after he saw that respiration and anion absorption had a quantitative link, but that cation absorption lacked such a relationship. Also observed was that cyanide or even carbon monoxide impeded salt respiration and anion absorption. He consequently proposed that the cytochrome system may transport anions across the membrane and that anion absorption is independent of the cation. Using respiratory intermediates directly as fuel, energy is produced. “Anion respiration” or “salt respiration” is the term used to describe the rate of respiration that is completely governed by anion absorption. Ground respiration is the rate of respiration (apart from anion respiration) that is seen in distilled water.
Total respiration t= Ground respiration + Salt or anion respiration

Ion Absorption: Selectivity, Accumulation, Genotype, and, Mechanisms of Ion Absorption

The soil solution contains the ions of the important plant mineral nutrients that are taken up by plant roots. Even if the concentration may be low, the anions and cations that are freely dissolved in the soil solution are the most easily assimilated by the roots. There are three ways in which these nutrients reach near roots:
(1) Ions diffusing through the soil solution
(2) The passively charged ions carried by the bulk flow of water into the roots and
(3) Roots’ development is extended toward the dissolved ions. Ion uptake is characterized by three principles in both higher and lower plants.

Mineral Nutrition: Definition, Essential elements, Beneficial elements, Macronutrients, Micronutrients, Importance of Macro and Microelements, Toxicity of Micronutrients 

Mineral nutrition refers to how different inorganic substances or minerals are absorbed, distributed, and metabolised by plants for their physiology, structure, and reproductive processes. Van Helmont conducted the initial investigation on inorganic or mineral nutrition in 1648.
Criteria for Essentiality of Elements
The Nutrients or Mineral elements that are necessary for a plant’s proper growth are referred to as Essential Nutrients or Essential Elements. 17 elements are considered vital. The term “essential mineral element” was first proposed by Arnon and Stout in the year 1939. They established that an element must satisfy the following three requirements to be considered essential.
1. Without the mineral element, a plant must be unable to finish its life cycle.
2. No other mineral element may perform the function of the element.
3. The element must be required for a specific metabolic phase, such as an enzymatic reaction, or it must be directly involved in plant metabolism, such as being a part of an enzyme that is an essential plant component.
Beneficial elements
Beneficial elements are those that promote growth but are not needed for all plant species or may become essential for some species under particular circumstances. Crop plants’ genetic potential cannot be maximised if the agricultural production system does not have advantageous components.
According to the essentiality criterion, mineral elements are required for specific metabolic processes in plants. Therefore, depending on the demand for a nutrient element to generate maximum plant growth, the nutrient is referred to as either Macronutrient or Micronutrient.
The Macronutrients are required in larger quantities and are available in plant tissues in amounts ranging between 0.2 and 4.0 % (on a dry weight basis).
While the amount of micronutrients in plant tissue is less than 0.02% and ranges from 5 to 200 ppm.
According to their needs, the macronutrients are further divided into primary macronutrients, which include nitrogen, phosphorus, and potassium, and secondary macronutrients, which include calcium, sulphur, and magnesium. Another classification of nutrients into metals (K, Ca, Mg, Fe, Mn, Zn, Cu, Mo, Ni) and non-metals is (N, S, P, B, Cl). However, rather than physiochemical characteristics, the most common classification is based on the quantity of mineral element requirements.

Importance of Macro and Microelements
The Macro- and Micronutrient elements can be divided into four groups as shown below (Malik and Srivastava 1982) for ease of understanding.
1. Nitrogen(N) and Sulphur(S) have covalently linked components of biological matter that are present in reduced form
2. Phosphate, borate, and silicate are examples of oxyanions that appear as P, B, and Si.
3: K, Na, Mg, Ca, and Cl play distinct roles in enzyme conformation and catalysis in addition to being engaged in osmoregulation and ionic equilibrium (e.g. metalloprotein complexes)
4: Metalloproteins or structural chelates of Fe, Cu, Mo, and Zn are present and also participate in oxidation-reduction (redox) reactions (first three elements)

Stomatal Movement: Opening and Closing of Stomata, Mechanism, Antitranspirants, and Guttation

Stomatal Movement: Opening and Closing of Stomata, Mechanism, Antitranspirants, and Guttation Opening and Closing of Stomata The distinctive shape of the stomata makes them distinct from the nearby epidermal cells. The epidermal cells that surround the stomata nearby can resemble other epidermal cells or they can be unique and specialised. They are referred to as …

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Transpiration: Definition, Types, Factors, and Significance

Transpiration As a Necessary Evil,
1. When the rate of transpiration is high and the soil is water-deficient, the plants may experience an internal water deficit that affects metabolic functions.
2. To control transpiration, many xerophytes must undergo structural modifications and adaptations.
3. To prevent water loss, deciduous trees must lose their leaves in the fall.
However, despite the numerous drawbacks, plants must transpire because of their unusual internal structure, especially that of their leaves. Although primarily intended for gaseous exchange for respiration, P.S., etc., their interior structure is such that it cannot prevent water from evaporating. As a result, several scientists, including Curtis (1926), have referred to transpiration as a necessary evil.

Transport across the plasma membrane: Passive transport, Active Transport, For Class 10th, 11th,  12th, and NEET

Facilitated Diffusion
This is the passage of particular molecules through the membrane using a particular carrier protein and a concentration gradient. Thus, each carrier has its structure and only permits one molecule (or one set of closely related compounds) to pass through, similar to how enzymes do.
Selection is based on size, shape, and charge. Glucose and amino acids are typical substances that enter or exit cells in this manner.
It uses no energy from the cell and is passive. The concentration gradient of glucose will be maintained high if the molecule is altered upon entry into the cell (glucose + ATP → glucose phosphate + ADP), resulting in constant one-way traffic.