Category: Biology
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Adenosine Triphosphate (ATP): Definition, Function, and Mechanism
Continue ReadingWhat is Adenosine Triphosphate (ATP)?
Adenosine triphosphate, otherwise called ATP, is a molecule that conveys energy inside cells.
It is the primary energy source of the cell, and it is a finished result of the cycles of photophosphorylation (adding a phosphate gathering to a molecule utilizing energy from light), cell breath, and maturation.
All living things use ATP. As well as being utilized as a fuel source, it is likewise utilized in signal transduction pathways for cell correspondence and is joined into deoxyribonucleic acid (DNA) during DNA combination.
Structure of Adenosine Triphosphate (ATP)
This is an underlying graph of ATP. It is comprised of the molecule adenosine (which itself is comprised of adenine and a ribose sugar) and three phosphate gatherings.
It is dissolvable in water and has a high energy content due to having two phosphoanhydride bonds interfacing the three phosphate affairs.
Features of Adenosine Triphosphate (ATP)
ATP is the primary transporter of energy that is utilized for all cell exercises. At the point when ATP is hydrolyzed and changed over to adenosine diphosphate (ADP), energy is delivered.
The expulsion of one phosphate bunch discharges 7.3 kilocalories per mole, or 30.6 kilojoules per mole, under standard conditions.
This energy controls all responses that occur inside the cell.
ADP can likewise be changed over once more into ATP, so the energy is accessible for other cell responses.
ATP is delivered through a few unique techniques. Photophosphorylation is a methodology express to plants and cyanobacteria. It is the formation of ATP from ADP utilizing energy from daylight and happens during photosynthesis.
ATP is additionally shaped from the interaction of cell breath in the mitochondria of a cell. This can be through vigorous breath, which requires oxygen, or anaerobic breath, which doesn’t.
High sway produces ATP (close by carbon dioxide and water) from glucose and oxygen.
Anaerobic breath utilizes synthetic substances other than oxygen, and this cycle is basically utilized by archaea and microscopic organisms that live in anaerobic conditions.
Aging is another method of delivering ATP that doesn’t need oxygen; it is not quite the same as anaerobic breath since it doesn’t utilize an electron transport chain.
Yeast and microbes are examples of life forms that utilization aging to create ATP.
Adenosine Triphosphate (ATP) and Signal Transduction
ATP is a flagging molecule utilized for cell correspondence. Kinases, which are catalysts that phosphorylate particles, use ATP as a wellspring of phosphate gatherings.
Kinases are significant for signal transduction, which is the way a physical or compound sign is sent from receptors outwardly of the phone to within the phone.
At the point when the sign is inside the cell, the cell can respond appropriately.
Cells might be offered signs to develop, utilize, separate into explicit kinds, or even pass on.
Adenosine Triphosphate (ATP) and DNA Synthesis
The nucleobase adenine is important for adenosine, an molecule that is framed from ATP and put straightforwardly into RNA.
The other nucleobases in RNA, cytosine, guanine, and uracil, are correspondingly framed from CTP, GTP, and UTP.
Adenine is likewise found in DNA, and its consolidation is practically the same, with the exception of ATP is changed over into the structure deoxyadenosine triphosphate (dATP) prior to turning out to be essential for a DNA strand.
Where Adenosine Triphosphate (ATP) Manufactured?
Numerous cycles are equipped for creating ATP in the body, contingent upon the current metabolic conditions. ATP creation can happen within the sight of oxygen from cells respiration, beta-oxidation, ketosis, lipid, and protein catabolism, just as under anaerobic conditions.
i. Cell Respiration
Cell breath is the way toward catabolizing glucose into acetyl-CoA, creating high-energy electron transporters that will be oxidized during oxidative phosphorylation, yielding ATP.
During glycolysis, the initial step of cell breath, one particle of glucose separates into two pyruvate atoms. During this interaction, two ATP are delivered through substrate phosphorylation by the compounds PFK1 and pyruvate kinase.
There is additionally the creation of two diminished NADH electron transporter particles.
The pyruvate atoms are then oxidized by the pyruvate dehydrogenase complex, shaping an acetyl-CoA particle. The acetyl-CoA atom is then completely oxidized to yield carbon dioxide and decreased electron transporters in the citrus extract cycle.
After finishing the citric acid cycle, the complete yield is two particles of carbon dioxide, one likeness ATP, three atoms of NADH, and one atom of FADH2.
These high-energy electron transporters then, at that point move the electrons to the electron transport chain in which hydrogen particles (protons) are moved against their inclination into the inward layer space from the mitochondrial framework.
ATP particles are then incorporated as protons dropping down the electrochemical inclination power ATP synthase.
The amount of ATP delivered changes relying upon which electron transporter gave the protons. One NADH particle produces more than two ATP, though one FADH2 atom produces one and a half ATP molecules.
ii. Beta-Oxidation
Beta-oxidation is another method for ATP blend in organic entities. During beta-oxidation, unsaturated fat chains are forever abbreviated, yielding Acetyl-CoA atoms.
All through each pattern of beta-oxidation, the unsaturated fat is diminished by two carbon lengths, creating one particle of acetyl-CoA, which can be oxidized in the citrus extract cycle, and one atom every one of NADH and FADH2, which move their high energy electron to the vehicle chain.
iii. Ketosis
Ketosis is a response that yields ATP through the catabolism of ketone bodies. During ketosis, ketone bodies go through catabolism to create energy, producing 22 ATP particles and two GTP atoms for every acetoacetate atom that gets oxidized in the mitochondria.
iv. Anaerobic Respiration
At the point when oxygen is scant or inaccessible during cell breath, cells can go through anaerobic breath.
During anaerobic conditions, there is a development of NADH atoms because of the failure to oxidize NADH to NAD+, restricting the activities of GAPDH and glucose utilization.
To keep up with homeostatic degrees of NADH, pyruvate is diminished to lactate, yielding the oxidation of one NADH atom in a cycle known as lactic maturation.
In lactic aging, the two particles of NADH made in glycolysis are oxidized to keep up with the NAD+ repository. This response delivers just two atoms of ATP for every particle of glucose.
Molecules Similar to Adenosine Triphosphate (ATP)
Different molecules are identified with ATP and have comparable names, for example, adenosine diphosphate (ADP), adenosine monophosphate (AMP), and cyclic AMP (cAMP).
To stay away from disarray, know a few contrasts between these particles.
i. Adenosine Diphosphate (ADP)
Adenosine diphosphate (ADP), which is at times otherwise called adenosine pyrophosphate (APP), particularly in science, has effectively been referenced in this article. It differs from ATP since it possesses two phosphate groups. ATP becomes ADP with the passing of a phosphate gathering, and this response discharges energy. ADP itself is framed from AMP. Cycling among ADP and ATP during cell breath gives cells the energy expected to do cell exercises.
ii. Adenosine monophosphate (AMP)
Adenosine monophosphate (AMP), additionally called 5′- adenylic corrosive, has just a single phosphate bunch. This particle is found in RNA and contains adenine, which is essential for the hereditary code. It tends to be delivered alongside ATP from two ADP molecules, or by hydrolysis of ATP.
It is additionally shaped when RNA is separated. It very well may be changed over into uric corrosive, which is a part of pee, and discharged through the bladder.
iii. Cyclic Adenosine monophosphate (cAMP)
Cyclic adenosine monophosphate (cAMP) is gotten from ATP and is another courier utilized for signal transduction and actuating certain protein kinases.
It very well may be separated into AMP. cAMP pathways may assume a part in specific diseases like carcinoma. In microorganisms, it has a job in digestion.
At the point when a bacterial cell isn’t delivering sufficient energy (from deficient glucose, for example), high cAMP levels happen, and this turns on qualities that utilization fuel sources other than glucose.
Adenosine Triphosphate (ATP) Citations
- Adenosine triphosphate and adenosine diphosphate in human semen: correlation with sperm count and motility. Urol Int . 1992;48(4):391-4.
- Intravenous adenosine triphosphate (ATP) in hemorrhagic shock in rats. Am J Physiol . 1981 Jan;240(1):R52-60.
- Adenosine triphosphate treatment for supraventricular tachycardia in infants. Eur J Pediatr . 1994 Sep;153(9):668-71.
- Imaging Adenosine Triphosphate (ATP). Biol Bull . 2016 Aug;231(1):73-84.
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Plant Growth Hormone Abscisic Acid: Definition, Mechanism,...
Continue ReadingGrowth Hormone: Abscisic Acid
Growth and development of an organism depends upon the internal and external factors supporting the growth of organism.
The external environmental cues are essential for the stimulation of growth and development for reproduction and survival efficiency of these environmental cues (i.e.) stimulus process the internal response of the organism.
The response is manifested and cell functions corresponding to the response is recorded. Such stimulus and response are well coordinated in the plant body by the chemical messengers – the hormones.
Hormones acts as a mediator for carrying and transferring information for the coordination of physiological, metabolic and chemical activity.
For example: the growth of coleoptile of Phalaris canariensis towards the light is the coordinated movement for external stimulus light (i.e.) the phototropism is mediated by the hormone auxin. This was the initial discovery for the presence of phytohormones in plant system regulating the function of whole plant body.
These chemical compounds enhance cell communication and integrate the multicellular organism to organized as a single unit.
Further studies were undergoing for the deducing the mechanism and variety of hormones coordinating plant body.
Between 1950 – 1960 a group of five hormones were identified to maintain the plant homeostasis. These hormones were combinedly termed as ” Classical Five” they are: AUXIN, CYTOKININ, ETHYLENE, GIBBERELLIN, ABSCISIC ACID.
Along with classical five there are brassanosteroids and jasmonic acid. These set of hormones are termed as “Plant Growth Regulators” as they have an active role in regulating growth and development rather than a broad action spectrum.
Hormones are sensitive, specific, low concentration action and are naturally occurring in plant species. These important characteristic makes it an ideal small molecule chemical messengers and regulators.
The mode of action is receptor mediated and are transported to different regions by vascular tissues(i.e.) xylem and phloem. Hormones like ethylene are volatile, hence they are diffused throughout the plant body.
Abscisic Acid Discovery
Discovery of ABA took place between 1950 – 1960, scientists had a hunch that when a growth stimulating endogenous hormones are present in the plant cell, growth inhibiting hormones which causes the senescence or abscission of fruits must be governed by other hormones namely Abscisic Acid (ABA).
ABA does not cause abscission they just inhibit growth.
Functions of Abscisic Acid
1. Inhibits growth and metabolism based on the developmental stage
2. Growth and inhibition of root is variable when ABA is present in them
3. Increases stress tolerance
4. Seed development and maturation enables seed to withstand desiccation.
Abscisic Acid Biosynthesis
ABA are synthesised from Xanthophylls namely Violaxanthin and neoxanthin.
Epoxidation or the presence of epoxy – carotenoids is necessary for the synthesis of ABA.
The synthesis however initiates from IPP forming GGPP further leads to the formation of Zeaxanthin produces violaxanthin. Violaxanthin forms cis – neoxanthin followed by cis – xanthin produces ABA Aldehyde leads to ABA.
Site of Synthesis: In mature leaves and stems and in developing fruits, seeds, etc.,
Regulation of Abscisic Acid Levels
1. Synthesis
2. Conjugation
3. Oxidation to inactive forms
Abscisic Acid Citations
- Abscisic acid: emergence of a core signaling network. Annu Rev Plant Biol . 2010;61:651-79.
- Abscisic acid biosynthesis and catabolism. Annu Rev Plant Biol . 2005;56:165-85.
- Abscisic acid: biosynthesis, inactivation, homoeostasis and signalling. Essays Biochem . 2015;58:29-48.
- Abscisic acid dynamics, signaling, and functions in plants. J Integr Plant Biol . 2020 Jan;62(1):25-54.
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Plant Growth Hormone Auxin: Definition, Mechanism, and...
Continue ReadingWhat is Auxin?
Growth and development of an organism depends upon the internal and external factors supporting the growth of organism.
The external environmental cues are essential for the stimulation of growth and development for reproduction and survival efficiency of these environmental cues (i.e.) stimulus process the internal response of the organism.
The response is manifested and cell functions corresponding to the response is recorded. Such stimulus and response are well coordinated in the plant body by the chemical messengers – the hormones.
Hormones acts as a mediator for carrying and transferring information for the coordination of physiological, metabolic and chemical activity.
For example: the growth of coleoptile of Phalaris canariensis towards the light is the coordinated movement for external stimulus light (i.e.) the phototropism is mediated by the hormone auxin. This was the initial discovery for the presence of phytohormones in plant system regulating the function of whole plant body.
These chemical compounds enhance cell communication and integrate the multicellular organism to organized as a single unit.
Further studies were undergoing for the deducing the mechanism and variety of hormones coordinating plant body.
Between 1950 – 1960 a group of five hormones were identified to maintain the plant homeostasis. These hormones were combinedly termed as ” Classical Five” they are: AUXIN, CYTOKININ, ETHYLENE, GIBBERELLIN, ABSCISIC ACID.
Along with classical five there are brassanosteroids and jasmonic acid. These set of hormones are termed as “Plant Growth Regulators” as they have an active role in regulating growth and development rather than a broad action spectrum.
Hormones are sensitive, specific, low concentration action and are naturally occurring in plant species. These important characteristic makes it an ideal small molecule chemical messengers and regulators.
The mode of action is receptor mediated and are transported to different regions by vascular tissues(i.e.) xylem and phloem. Hormones like ethylene are volatile, hence they are diffused throughout the plant body.
Auxin Discovery
Auxins are naturally occurring Indole 3 – Acetic Acid that are abundant and can exist as non-indole component too.
Auxin in Greek means – “to grow” or “to increase”.
The main function of auxin is cell division.
The Dutch biologist Frits Warmolt Went was the one who first described auxins and their role in plant growth.
In the 1920s Kenneth V. Thimann (1904-1997) became the first to isolate one of these phytohormones and to determine its chemical structure as indole-3-acetic acid (IAA).
Auxin Functions
1. Growth from embryo to adult
2. Cell division
3. Stem elongation
4. Apical dominance
5. Fruit development
6. Tropic responses
Auxin Biosynthesis
Conclusive research analysis or findings are not available for the biosynthesis of IAA because of minimal availability of hormones.
Many studies have concluded that Tryptophan to be the precursor for IAA. The synthesis initiates from Erythrose – 4 phosphate of pentose phosphate pathway which on further degradation provides tryptophan.
Tryptophan has many precursors from which many mechanisms are followed to produce Tryptophan.
Tryptophan deaminates to Indole – 3 -pyruvic acid which on decarboxylation produce indole – 3 – acetaldehyde on oxidation yields Indole Acetic Acid.
Though the synthesis and pathways deduced for tryptophan’s to be the precursor for IAA many bioassays and other techniques has proved that there are precursors other than Tryptophan from which IAA is synthesized.
A conclusion can be laid that the IAA can be synthesized by tryptophan dependent process and Tryptophan Independent process.
Site of biosynthesis: site of biosynthesis is dependent on endogenous precursor pools.
The precursors are not well defined for IAA. But, based on the existing analysis it can be detected that tryptophan are rich in plastids and it also has a cytoplasmic pool in plant cell.
Hence plastids and cytoplasm of plant cell can be assumed as site of biosynthesis.
An affirmation regarding the site of synthesis of auxin can be provided considering the presence of Auxin in the Apical meristematic zones and are absent in mature cell.
Regulation of Auxin Levels
Hormones are regulated by variety of mechanisms. They are – Synthesis, Conjugation, Irreversible modification breakdown, transportation and compartmentation.
Lesser the knowledge of biosynthesis of Auxin lesser the role of regulation identified for auxins. It is regulated by formation of conjugates and irreversible modification by breakdown of IAA.
Conjugation: IAA forms conjugates with ester linkage to sugar or alcohol or to amino acids by amide linkage.
Breakdown: IAA is decarboxylated with products: oxindole – 3 – methanol, 3 – methylene oxindole, 3 – methyl oxindole, indole – 3 aldehyde.
Auxin Inhibitors
IAA are inhibited by synthetic compounds. These compounds inhibit IAA and not the synthesis.
These inhibiting molecules are called antiauxins. They inhibit by binding to the receptors of IAA.
Auxin Citations
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Plant Growth Hormone Cytokinin: Definition, Mechanism, and...
Continue ReadingPlant Growth Hormone: Cytokinin
Growth and development of an organism depends upon the internal and external factors supporting the growth of organism.
The external environmental cues are essential for the stimulation of growth and development for reproduction and survival efficiency of these environmental cues (i.e.) stimulus process the internal response of the organism.
The response is manifested and cell functions corresponding to the response is recorded. Such stimulus and response are well coordinated in the plant body by the chemical messengers – the hormones.
Hormones acts as a mediator for carrying and transferring information for the coordination of physiological, metabolic and chemical activity.
For example: the growth of coleoptile of Phalaris canariensis towards the light is the coordinated movement for external stimulus light (i.e.) the phototropism is mediated by the hormone auxin. This was the initial discovery for the presence of phytohormones in plant system regulating the function of whole plant body.
These chemical compounds enhance cell communication and integrate the multicellular organism to organized as a single unit.
Further studies were undergoing for the deducing the mechanism and variety of hormones coordinating plant body.
Between 1950 – 1960 a group of five hormones were identified to maintain the plant homeostasis. These hormones were combinedly termed as ” Classical Five” they are: AUXIN, CYTOKININ, ETHYLENE, GIBBERELLIN, ABSCISIC ACID.
Along with classical five there are brassanosteroids and jasmonic acid. These set of hormones are termed as “Plant Growth Regulators” as they have an active role in regulating growth and development rather than a broad action spectrum.
Hormones are sensitive, specific, low concentration action and are naturally occurring in plant species. These important characteristic makes it an ideal small molecule chemical messengers and regulators.
The mode of action is receptor mediated and are transported to different regions by vascular tissues(i.e.) xylem and phloem. Hormones like ethylene are volatile, hence they are diffused throughout the plant body.
Cytokinin Discovery
Discovery of cytokinin was first started from Haberlandt, German plant physiologist in 1913 that the phloem extracts are used to cause cell division in tubers.
In 1921, from another experiment he found that cell division is promoted by soluble factor.
In 1940’s and 1950’s the cell culture techniques were practiced, where the addition of auxins did not yield cell division. but on addition of autoclaved herring sperm initiated rapid cell division.
The substance that promoted the cell division was named Kinetin. Later naturally occurring zeatin were discovered.
Functions of Cytokinin
1. Promotes cell division in callus and tissue
2. Auxin and Cytokinin combines together to form a shoot bud vs root growth in tissue culture and stem cuttings
3. Regulate Apical Dominance and lateral root initiation
4. Retard senescence and chlorophyll degradation
5. Present in major parts of plant
Cytokinin Biosynthesis
IPP is the key for cytokine synthesis.
IPP isomerize with DMAPP.
DMAPP condense with AMP give rise to iso – pentenyl adenosine mono phosphate (iPMP).
iPMP is precursor for all naturally occurring Cytokinins.
iPMP is hydroxylated at C4 of the side chain and forms zeatin riboside.
In further steps, Ribose and phosphate are cleaved to yield Zeatin.
Site of synthesis: primarily synthesized in meristematic tissues.
Regulation of Cytokinin Levels
1. It is regulated by conjugation of Cytokinins
2. Irreversible inactivation
Cytokinin Citations
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Plant Hormone Ethylene: Definition, Mechanism, and Function
Continue ReadingEthylene: a Plant Growth Hormone
Growth and development of an organism depends upon the internal and external factors supporting the growth of organism.
The external environmental cues are essential for the stimulation of growth and development for reproduction and survival efficiency of these environmental cues (i.e.) stimulus process the internal response of the organism.
The response is manifested and cell functions corresponding to the response is recorded. Such stimulus and response are well coordinated in the plant body by the chemical messengers – the hormones.
Hormones acts as a mediator for carrying and transferring information for the coordination of physiological, metabolic and chemical activity.
For example: the growth of coleoptile of Phalaris canariensis towards the light is the coordinated movement for external stimulus light (i.e.) the phototropism is mediated by the hormone auxin. This was the initial discovery for the presence of phytohormones in plant system regulating the function of whole plant body.
These chemical compounds enhance cell communication and integrate the multicellular organism to organized as a single unit.
Further studies were undergoing for the deducing the mechanism and variety of hormones coordinating plant body.
Between 1950 – 1960 a group of five hormones were identified to maintain the plant homeostasis. These hormones were combinedly termed as ” Classical Five” they are: AUXIN, CYTOKININ, ETHYLENE, GIBBERELLIN, ABSCISIC ACID.
Along with classical five there are brassanosteroids and jasmonic acid. These set of hormones are termed as “Plant Growth Regulators” as they have an active role in regulating growth and development rather than a broad action spectrum.
Hormones are sensitive, specific, low concentration action and are naturally occurring in plant species. These important characteristic makes it an ideal small molecule chemical messengers and regulators.
The mode of action is receptor mediated and are transported to different regions by vascular tissues(i.e.) xylem and phloem. Hormones like ethylene are volatile, hence they are diffused throughout the plant body.
Ethylene Discovery
Discovery of ethylene was done by Dimitry Neljubov. He was growing pea seedling in dark and the laboratory was gas lit, instead of elongating apical stem, the stem is shortened and had stunted growth. the gas lit lab had an ethylene leak which stunted the plant growth by inhibiting it.
From the experiment, ethylene was identified to be reducing the growth rate of plants.
In 1930 endogenous ethylene pools were identified in plant material especially in fruits that are ripened.
Functions of Ethylene
1. Fruit ripening
2. Promotes senescence and abscission
3. Root hair production
4. Seed germination
5. Sprout lateral buds
Ethylene Biosynthesis
Methionine is the precursor for ethylene on addition of Adenosine group from ATP forms Ado Met. Ado Met cleaves to produce Aminocyclopropanecarboxylic acid and Methylthioadenosine.
ACC on enzyme catalyses yields ethylene. MTA is cleaved by adenosine and give rise to adenine and methylthioribose.
MTR on further steps yields methionine for the cycle to proceed.
Site of Synthesis: Ripening regions and in senescing leaves and other parts.
Regulation of Ethylene Levels
Ethylene synthesis is regulated by certain inhibitors
The production of ethylene itself becomes an indicator to inhibit the production.
Conjugation of ACC
Oxidation of ethylene
Inhibitors of Ethylene Synthesis
Methyl cyclopropane, Dimethyl cyclopropane
Ethylene Citations
- The Pivotal Role of Ethylene in Plant Growth. Trends Plant Sci . 2018 Apr;23(4):311-323.
- Ethylene signaling in plants. J Biol Chem . 2020 May 29;295(22):7710-7725.
- The ethylene pathway: a paradigm for plant hormone signaling and interaction.
- Ethylene signaling in rice and Arabidopsis: conserved and diverged aspects. Mol Plant . 2015 Apr;8(4):495-505.
- Perception of the plant hormone ethylene: known-knowns and known-unknowns. J Biol Inorg Chem . 2016 Sep;21(5-6):715-28.
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Gibberellin: Definition, Mechanism, and Function
Continue ReadingGrowth Hormone: Gibberellin
Growth and development of an organism depends upon the internal and external factors supporting the growth of organism.
The external environmental cues are essential for the stimulation of growth and development for reproduction and survival efficiency of these environmental cues (i.e.) stimulus process the internal response of the organism.
The response is manifested and cell functions corresponding to the response is recorded. Such stimulus and response are well coordinated in the plant body by the chemical messengers – the hormones.
Hormones acts as a mediator for carrying and transferring information for the coordination of physiological, metabolic and chemical activity.
For example: the growth of coleoptile of Phalaris canariensis towards the light is the coordinated movement for external stimulus light (i.e.) the phototropism is mediated by the hormone auxin. This was the initial discovery for the presence of phytohormones in plant system regulating the function of whole plant body.
These chemical compounds enhance cell communication and integrate the multicellular organism to organized as a single unit.
Further studies were undergoing for the deducing the mechanism and variety of hormones coordinating plant body.
Between 1950 – 1960 a group of five hormones were identified to maintain the plant homeostasis. These hormones were combinedly termed as ” Classical Five” they are: AUXIN, CYTOKININ, ETHYLENE, GIBBERELLIN, ABSCISIC ACID.
Along with classical five there are brassanosteroids and jasmonic acid. These set of hormones are termed as “Plant Growth Regulators” as they have an active role in regulating growth and development rather than a broad action spectrum.
Hormones are sensitive, specific, low concentration action and are naturally occurring in plant species. These important characteristic makes it an ideal small molecule chemical messengers and regulators.
The mode of action is receptor mediated and are transported to different regions by vascular tissues(i.e.) xylem and phloem. Hormones like ethylene are volatile, hence they are diffused throughout the plant body.
Gibberellin Discovery
Gibberellins were discovered from a Japanese crop disease “Bakanae” where the crops are subjected to elongated and weak growth caused by an ascomycetes Gibberella fujikuroi. the extracts from the fungi are collected and termed as Gibberellin by Yabuta and Hayashi.
In 1950’s, Europe and American scientists started to standardise methods of isolating hormones. On learning about Gibberellin, its function to elongate the stem was related to higher plants which have taller stems and branches.
When extracted the responding hormone scientists named it as GIBBERELLIN. Gibberellins are tetracycline diterpenoids prevalent in two forms. C20 – GA’s and C19 – GA’s out of this C19 GAs are found abundant in plant cell.
The variety of GA’s are increasing, presently there are about 125 GAs identified.
Functions of Gibberellins
1. they promote elongation in stem and root. Their role in cell division is nil but they elongate both root and shoot
2. During Seed germination, the stored starch, proteins and lipids are broken down by hydrolysis. GA’s promote hydrolysis during seed germination.
3. Floral development
4. Phloem tissue differentiation
5. Cambial Reactivation
Gibberellin Biosynthesis
Out of all Plant Growth Regulators, GA’s are very well studies and biosynthesis are well known.
Terpenes are secondary products of plants is defensive in function prevents plant from plant feeding Insects.
Apart from the defence terpenes helps in photosynthesis, membrane stability and signalling Isoprene a C5 structure is the base for all terpenes.
The isomerization of isopentenyl diphosphate yields dimethylallyl diphosphate following condensation yields C10 terpenes, C15 terpenes on further condensation gives C30 and C40 terpenes.
IPP was synthesized by mevalonic acid dependent pathway or by Mevalonic Acid Independent pathway by Pyruvate and Glyceraldehyde.
Synthesis takes place in 3 stages:
Stage 1: Geranylgeranyl Diphosphate (GGPP) undergoes cyclation to form ent – kaurene followed by enzyme catalysation takes place in Plastids.
Stage 2: Oxidations leads to the formation of ent – kaurenoic acid hydroxylated to form ent -7alpha kaurenoic acid later yields G12 Aldehyde
Stage 3: GA12 – aldehyde yields GA12. 13 – Hydroxylation leads to the formation of GA53. Oxidations at C20 leads to lactone formation.
Regulation of Gibberellin Levels
Levels of GA are maintained by plant tissues
Their inactivation is done by conjugation or catabolic breakdown
Irreversible inactivation, transport to different parts of the plant, storage in compartments such as vacuoles.
Gibberellin Citations
- Gibberellin biosynthesis and its regulation. Biochem J . 2012 May 15;444(1):11-25.
- Gibberellin metabolism and its regulation. Annu Rev Plant Biol . 2008;59:225-51.
- Gibberellin Localization and Transport in Plants. Trends Plant Sci . 2018 May;23(5):410-421.
- Gibberellin signaling in plants. Development . 2013 Mar;140(6):1147-51.
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Plant Growth Regulators: Definition, Types, and Mechanism
Continue ReadingWhat are Plant Growth Regulators?
The plant growth which is irreversible, progressive and unlimited is mainly because of the fact that specialized meristem regions are capable of having an indefinite cell division when required and are regulated by internal factors.
Genetic makeup and other physiological factors namely hormones are responsible for the condition of unlimited growth of the plant.
Unique set of hormones are well developed which regulates the development of the plant in a way where it balances the growth of the plant and it retains it by a gradual process.
Plant Growth Regulators (PGR) are hormones which acts on cells to promote and inhibit when stimulated.
Plant Growth Regulators and hormones are similar terms, hormones generally cover a broad portion of compounds and Plant Growth Regulators’s are plant hormones or phytohormones which are specialized in cell division, elongation, growth of a plant body.
Hormones are simple molecules having varied diverse composition.
They are required in minimal amount for the growth of organism
Plant Growth Regulators History
The discovery was accidental and had many experimentations while concluding its actions.
Charles Darwin and Francis Darwin observed the plant response to light and uneven growth towards light was observed. Between 1950 – 1960 a group of hormones were discovered and were named as “classical five” – Auxin, Gibberellin, Abscisic Acid, Ethylene and Cytokinin.
Following this many natural and synthetic regulators were discovered later.
Characteristics of Plant Growth Regulators
• Hormones are pleiotropic in nature
Example: Auxin helps in cell division, elongation, apical dominance etc.
• Several hormones act for same responses leads to reduced response for a particular stimuli / action
• Small concentration is required
• Hormones are synthesized at different parts of the plant body and are transported to the site of action
• Hormone action is time specific and precise
• Hormones can be stimulator or inhibitor
Types of Plant Growth Regulators
Plant hormones are of 2 types:
1. Growth promoters: promote cell division, cell elongation, pattern formation, seed and fruit development
2. Responser: Biotic and Abiotic cues response and for stressors
Plant Growth Regulators and Their Functions
I. Auxin
• Naturally occurs as Indole 3 Acetic Acid.
• Synthesis: Leaf primordia and young leaves
• Transportation: flows through phloem
• Induces overall polarity of root shoot polarity
• Basipetal transportation of hormones from tips of leaf to the leaf and stem and similarly, root tips → root – shoot differentiation zone.
• Apical dominance reduces the Abscission in apical region
• Auxin are signal mediated multiple level coordinated developmental processes
II. Cytokinin
• Promote cell division
• Transported to shoot from root through Xylem
• Activates lateral bud formation
• Pro – vascular tissue formation
• Positive geotropism is observed
• Inhibitors of root development and control meristem activity
III. Ethylene
• Simple hydrocarbon which is volatile
• Present in Seeds of all plants
• Transportation by: Diffusion
• Production sites: shoot apices, nodal region of stem
• Ripening process in climacteric fruits
• High production during stress
• Ethylene promotes leaf abscission
IV. Abscisic Acid
• Present throughout the plan body
• Aids in Abscission triggered by ethylene
• Transportation: Xylem and Phloem. Abundant in Phloem
• When water is in excess, ABA transports to stomata through xylem which induces stomatal closure
• High production during seed protein synthesis and seed development
• Break dormancy in seeds
V. Gibberellins
• Tetracyclic diterpenoids
• In seed and fruit development
• Growth of bud, Leaves, Internodes
• Transportation via Phloem
• Stem and leaf elongation also in root elongation and pollen tube growth
• Secretes enzymes
Plant Growth Regulators Citations
- Oligosaccharins as plant growth regulators. Biochem Soc Symp . 1994;60:5-14.
- On plant growth regulators and their metabolites: a changing perspective. Semin Cell Biol . 1993 Apr;4(2):87-92.
- Synthesis and preliminary evaluation of dimeric-28-homobrassinosteroids for plant growth regulators. Steroids . 2016 Dec;116:38-44.
- An integrated network of Arabidopsis growth regulators and its use for gene prioritization. Sci Rep . 2015 Dec 1;5:17617.
- A high efficient adsorbent for plant growth regulators based on ionic liquid and β-cyclodextrin functionalized magnetic graphene oxide. Talanta . 2019 Mar 1;194:14-25.
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Cell Differentiation: Definition, Process, and Stages
Continue ReadingWhat is Cell Differentiation and Development?
Plant develops from a single celled zygote to multicellular, tissue level coordinated living being by the process of development and growth.
The development, growth, distinction between different parts of a organisms is determined by the genetic material by a gradual process of cell division.
Cell division is the primary process where continuous division leads to a pattern formation. The pattern formed is based on the symmetry of the division and the cytoplasmic distribution during cell division.
When a zygote becomes an 8 – celled blastomere the cytoplasmic contents of one cell are evenly or unevenly distributed in all cells.
Further, positioning of an embryo and environmental cues differentiates the cell further making each part of the cell a distinct and specified region.
This overall mechanism is a gradual process involving commitment, determination and differentiation.
The 3 processes are overlapping with negligible differences. Commitment is the determination of cell fate of a particular cell. Determination is similar to commitment where a part of the embryo gets determined to develop into a particular organ.
Differentiation is the process where the determined part divides and transforms to a specialized region with definite structure and function.
The differentiated parts get matured after the process. The main difference between plants and animal differentiation is unlimited growth in plants which demands an extra process called dedifferentiation and redifferentiation.
Elongation of leaves will initiate matured cell to dedifferentiate to gain its embryological function of continuous proliferation to attain desirable growth after which the cells attain its specific role which is redifferentiation.
Cell Division and Cell Differentiation
Cell division is crucial in differentiation of group of cells according to its functional and structural specificity.
The unequal distribution of proteins and other essential nutrients at each cell division to daughter cell determines the determination of each part and its differentiation.
The distribution may be supported by the cytoskeleton which transports and orients the nutrients appropriately.
Many scientists claim the asymmetrical cleavage leads to the formation of different parts. Formation of sieve cells, companion cells trichoblast are result of asymmetrical division of zygote.
Few scientists believe that nearly symmetrical daughter cells have different composition of cytoplasm.
The synthesis of protein and gene expression varies the mother cells composition from daughter cells.
In both the division the accumulation of varying composition of cytoplasm is essential in cell differentiation.
During such division the daughter cells does not inherit all the ability of mother cell. Each division restricts the differential ability of the cell making it more specific in nature.
Mechanism of Differentiation
Differentiation is by limiting gene transcription and expression of a cell which defines a cell’s function.
Other functions apart from prescribed function are eliminated or not expressed. Each differentiated region has separate function and specialized materials present in them.
For example: Mesophyll cells in leaf has 40 – 50 chlorophyll, 106 photoreceptors, chlorophyll a and b, enzyme essential for photosynthesis namely RUBISCO – Ribulose 1,5 – bisphosphate carboxylase/oxygenase.
Similarly in root cell, lacks chlorophyl, photoreceptors proteins of chlorophyll instead they carry starch storing plastids namely amyloplast. Both leaf and root contain same genomic DNA but expression of gene and other activities determines the part which the cell must occupy.
The mechanisms are monitored by 3 types of gene namely:
1. Housekeeping genes
2. Cell or tissue specific genes
3. Regulatory genes
Housekeeping genes are common genes which are widely present at any part of the body doing respiratory, storage sugar uptake, protein synthesis etc.,
Cell or tissue specific genes are present in all types of cells or tissue but gene expression is limited to a cell type or tissue.
For example:
a. Chlorophyll proteins, photoreceptors, RUBISCO enzyme are present only in the mesenchymal cells.
b. Amyloplast are present only in roots for storage purpose in parenchymal cells
c. PHENYLALANINEAMMONIA LYSE gene is present in seed. The enzyme encoding gene helps in lignin synthesis in xylem.
Regulatory genes, synthesis proteins involved in signaling. These are encoded by multigene complexes known as Homeobox genes which are specified in determining the pattern for future differentiation.
For example: Plant Homeobox genes determine the patterning of the future structure, determination of cell fate, defining boundaries between different tissues and organs.
KNOX I genes are specified for patterning shoot meristem and differentiates them from lateral organs by not expressing them in lateral part of the plant.
As a whole differential gene expression and inhibition combinedly forms differentiated parts of the tissue or plants.
Changes During Cell Differentiation
a. Endopolyploidy is observed in Angiosperm – chromosomes differentiate number of times without cell division is known as endopolyploidy.
b. Cell size increases unequally
c. Tissue expresses coordinate growth with intrusive cell growth where new cells are included in between the existing cells. The intrusive cell grows coordinated with existing cells. For example: root hair cell developing from root primordium.
Dedifferentiation
A matured cell changes its metabolic activity and modifies its gene function and attains its zygotic cell division abilities to divide and differentiate to new cells.
Changes During Dedifferentiation
a. Loss of stored food
b. Thinning cell wall
c. In cell culture, polar or amoeboid growth observed
d. Ploidy level changes
Changes During Re-differentiation
Once matured cells after dedifferentiation attains new additional functions than their previous matured state.
Cell Differentiation Citations
- Acidic cell elongation drives cell differentiation in the Arabidopsis root. EMBO J . 2018 Aug 15;37(16):e99134.
- Trichomes as models for studying plant cell differentiation. Cell Mol Life Sci . 2013 Jun;70(11):1937-48.
- Control of plant cell differentiation by histone modification and DNA methylation. Curr Opin Plant Biol . 2015 Dec;28:60-7.
- Emerging concepts in chromatin-level regulation of plant cell differentiation: timing, counting, sensing and maintaining. Curr Opin Plant Biol . 2016 Dec;34:27-34.
- In situ cell differentiation monitoring of Catharanthus roseus suspension culture processes by NIR spectroscopy. Bioprocess Biosyst Eng . 2020 Apr;43(4):747-752.
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Plant Development: Definition and Stages I Research...
Continue ReadingWhat is Plant Development?
Growth and development of any organism is closely associated with cell division and nutrient uptake by the organism.
The open form of growth produced by the meristem makes a plant have an unlimited growth and makes it unique mechanism for survival.
The life history of an organism is depicted as the development of organism from its birth to death.
The cumulative changes in the living system, physiological and metabolic activities, different phases of grow and reproduction are all an important aspect of development of an organism.
The development initiates from the zygote and covers the entire life processes including structural maturity and functional maturity.
The development is always about the pattern formation and combination of functions and is important as it ensures the survival of progeny and takes place in evolution of whole living organism.
Plant Development Process
The changes and modification taking place during the zygote differentiation corresponds with the developmental cues for the plant maturation and growth in the future.
The basic plan for survival is well laid in the zygote as basic differentiation becomes well defined and acts as a key for body plan of the whole organism.
The development is gradual and progressive takes place in a sequence, they are:
Plant Development Steps
1. The zygote, a highly organized precursor develops into embryo by embryogenesis
2. The 2 basic body patterns are formed by the asymmetrical division: apical -basal pattern and radial pattern.
3. Polarity of the cell is established and apical and basal part is determined
4. After subsequent cell division and differentiation, the meristematic tissue is formed
5. The primary meristematic tissues are protoderm, ground meristem and procambium
6. Cell divisions takes place now at the apical portion of the polar sides – bipolar differentiation distinguishing root and shoot.
7. The primary meristematic tissues formed are especially for the elongation.
8. These primary meristematic tissues now mature to form cotyledons forming a radicle and plumule – root and shoot primordia.
9. Cotyledons stages are seed germination period where the shoot differentiates into leaves, nodes and internodes.
10. The formation and development of root and shoot is the vegetative growth of the plant
11. On further differentiation when the apical meristem give rise to floral apical meristem this is the reproductive stage.
12. The primary successive growth results due to the apical meristem.
13. The primary tissues increase in thickness (i.e.) girth and enter secondary growth.
14. Secondary growth results in the radial thickening of the plant results in increase of cell division in secondary cambial growth.
15. The secondary growth meristem results in the production of vascular cambium – secondary vascular cambium tissues.
16. The lateral meristem aids in increase of volume of the secondary tissues.
17. The maturity of plant leads to the termination of plant’s life after the maturation and differentiation.
18. Senescence is the gradual programmed cell death which can be controlled by the chemical regulators of the plant
19. Senescence can also be caused by the accumulation of change which decreases the productivity if an organism causing death.
20. The development, differentiation and maturation is a gradual process, similarly the senescence is also a gradual process where the plant reduces the utilization of basic proteins for the synthesis of food and energy. Later reduced metabolism will lead to death of the plant under natural condition.
Plant Development Citations
- Plant Development: How Leaves Take Shape. Curr Biol . 2019 Aug 19;29(16):R803-R805.
- Phyllotaxis as geometric canalization during plant development. Development . 2020 Oct 12;147(19):dev165878.
- Shape and form in plant development. Semin Cell Dev Biol . 2018 Jul;79:1-2.
- Expanding roles for pectins in plant development. J Integr Plant Biol . 2018 Oct;60(10):910-923.
- Functions and Regulation of Programmed Cell Death in Plant Development. Annu Rev Cell Dev Biol . 2016 Oct 6;32:441-468.
- Cadmium and Plant Development: An Agony from Seed to Seed. Int J Mol Sci . 2019 Aug 15;20(16):3971.
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Aneuploidy: Definition, Types, Causes, and Examples
Continue ReadingWhat is Aneuploidy?
Generally, ploidy refers to the number, and here ploidy is the number of chromosomes present in the diploid set of homologous chromosomes that make up a genome of an organism.
Aneuploidy is one such type of ploidy, where the abnormal number of chromosomes are present in the individual where 45 or 47 chromosomes are present instead of 46.
Everything which are used up in pairs can be used only if their sets are available, considering from shoes, shocks, earrings, lenses, ear pods etc. Thus pairs are very important in the genetics where chromosomes play a key role in functioning of an organism in an appropriate manner.
Where the pair of chromosomes should be 2n, lesser or higher from this number causes many disorders and abnormality in an individual.
Aneuploidy is the condition where the person have a missing or an extra chromosome. Usually, any change in the number or structure of a chromosome is known as mutation and it is considered as one of the chromosomal disorders.
Chromosomal disorders are classified into two types based on the structural abnormality and numerical abnormality.
This numerical abnormality is further sub divided into euploidy and aneuploidy where euploidy is the condition where there is the presence of complete set of chromosomes (2n).
The other sub type is Aneuploidy where there is an addition or deletion in a 2n set of chromosomes.
Features of Aneuploidy
Aneuploidy is defined as the addition of an extra chromosome or removal or absence of a chromosome from any of its pair.
Each species contains a definite set of chromosomes where human contain 46 chromosomes which are 23 in pair to form a typical body cell and proper functioning of the parts.
If a cell contains one or two chromosomes extra or lesser than the normal pair then it is said to be aneuploidy.
This results in many disorders or abnormalities in a person, where in aneuploidy “an” refers to improper; and “ploidy” refers to number, and hence improper number of chromosomes causes this disorder.
Types of Aneuploidy
Aneuploidy is classified generally as hypoploidy and hyperploidy;
1. Hypoploidy
Hyploidy is generally defined as loss or lesser number of chromosomes compared with the normal 2n chromosomes.
The hyploidy is further sub divided as monosomy and nullisomy
Monosomy: Loss of one chromosome in a pair(2n-1)
Nullisomy: Loss of one pair (2n-2). The children having this condition has only lesser chance of leading a life.
2. Hyperploidy
This results in addition of one or more chromosomes. It is subdivided into types as
Trisomy: This condition results in extra chromosome on cells. It often results in Klinefelter’s syndrome with a trisomy in chromosome 21.
Tetrasomy: This condition results in addition of a pair of chromosomes.
Diploid: This condition results in addition of one chromosome in an monoploid organisms.
There are three most common types of aneuploidy that is occurring often; there are;
Monosomy
Here the organism contains one chromosome lesser (2n-1) in number than the normal, where humans contain 45 chromosomes instead of 46.
One of the examples for monosomy is TURNER’S SYDROME, where girls are mostly affected with this condition due to loss of one chromosome in the allosome set.
It leads to various developmental abnormalities and many severe symptoms.
The people with this condition are sterile in nature and short in stature and webbing of neck region is seen.
Trisomy
The individual contains addition of a n extra number of chromosomes. Which is 2n+1 in any one pair of the chromosome. Where they contain 47 chromosomes instead of 46.
One of the examples of trisomy is DOWN SYNDROME, which is due to the presence of an extra number in chromosome 21 which leads to many abnormalities.
It occurs mostly in 1 of 800 births. This factor mostly occurs if the child’s mothers age is above 35. This occurs due to the abnormal cell division during mitotic and meiotic phases.
The symptoms of this disorder include short stature, mental retardation, small head, poor muscle tone.
Causes of Aneuploidy
The chromosomal disorders mostly occur due to an occurrence of non-disjunction of chromosomes.
They occur when the two homologous sister chromosomes failed to separate during the stages of meiosis.
Meiosis I: In meiosis I the failure of non-disjunction of homologous chromosomes occurs during cell division.
Meiosis II: In Meiosis two, the failure of separation of sister chromatids occurs.
Mitosis: Non-disjunction of chromosomes also occurs in mitosis phases. In humans, the non-disjunction of chromosomes during mitosis does not pass through the next generation.
But in mitotic, non-disjunction causes other abnormalities. Cancer also occurs mostly due to the non-disjunction of chromosomes in the mitotic cells.
Considering an aneuploid condition, where the normal sperm combines with an aneuploid condition egg then it form an abnormal zygote as 2n+1 or 2n-1.
Where as in normal conditions normal sperm and a normal egg combines to form a normal zygote which is 2n.
Aneuploidy Citations
- A Double-Edged Sword: Aneuploidy is a Prevalent Strategy in Fungal Adaptation. Genes (Basel) . 2019 Oct 10;10(10):787.
- The impact of aneuploidy on cellular homeostasis. Free Radic Res . 2019 Jul;53(7):705-713.
- Oocyte development, meiosis and aneuploidy. Semin Cell Dev Biol . 2015 Sep;45:68-76.
- Aneuploidy Screening in Pregnancy. Obstet Gynecol . 2016 Jul;128(1):181-194.
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