The Discovery of Plant Growth Regulators Questions in English

(D) The discovery of plant growth regulators involved several key findings:
$1$. Auxins were first isolated from human urine by $F.W. Went$ and others.
$2$. Gibberellins were first discovered by $E. Kurosawa$ from the fungus $Gibberella$ $fujikuroi$ (which causes 'bakanae' disease in rice seedlings).
$3$. Cytokinins were first isolated from autoclaved herring sperm $DNA$,and later from corn germ oil (zeatin).
Therefore,the historical isolation of these natural plant hormones is primarily associated with human urine and rice seedlings (in the context of the discovery of gibberellins).

(D) The term 'phytohormones' was introduced by Kenneth $V$. Thimann in $1948$ to describe chemical substances that regulate plant growth and development. Therefore,the correct option is $D$.

(B) Plant growth regulators (PGRs),commonly known as plant hormones,are small,simple molecules of diverse chemical composition. These substances act as key regulators of plant growth and development by either promoting (e.g.,auxins,gibberellins,cytokinins) or inhibiting (e.g.,abscisic acid,ethylene) various physiological processes. Therefore,hormones are the primary substances that function as key growth regulators.

(B) Plant growth regulators,commonly known as plant hormones or phytohormones,are chemical substances produced in various parts of the plant,particularly at the tips of stems and roots (apical meristems).
These substances are transported to other parts of the plant where they regulate and control physiological processes such as growth,development,and differentiation of different organs.
Examples include auxins,which are primarily synthesized at the shoot and root apices.

(D) Julius von $Sachs$ was a German botanist who,in the late $19$th century,speculated that plants contain specific chemical substances responsible for organ formation.
He proposed that these substances are synthesized in different parts of the plant and are responsible for the growth and differentiation of organs.
These substances are now known as plant hormones or phytohormones.

(C) . Phytohormones are organic compounds produced in small quantities in plants. Historically, they were measured using bioassays. However, in modern analytical chemistry, techniques such as $Gas \text{ chromatography}$ $(GC)$, $High \text{ performance liquid chromatography}$ $(HPLC)$, and $Immunoassay$ techniques are primarily employed for the precise separation, identification, and quantification of these hormones.

(B) Plant growth regulators (PGRs),also known as $Phytohormones$,are small,simple molecules of diverse chemical composition.
These substances are produced naturally in plants and have a profound effect on growth and development even in very low concentrations.
Examples include auxins,gibberellins,cytokinins,ethylene,and abscisic acid.

(B) The discovery of the first plant growth hormone originated from the experiments conducted by $Charles$ $Darwin$ and his son $Francis$ $Darwin$. They observed that the coleoptile of canary grass ($Phalaris$ $canariensis$) exhibited phototropism (bending towards light) only when the tip was exposed to unilateral light.
Later, $Peter$ $Boysen-Jensen$ demonstrated that this signal was a chemical substance that could diffuse through a gelatin block, which was eventually identified as $Auxin$.

(A) Morphactins are synthetic growth regulators that act in a variety of ways on the natural regulation mechanisms of plants.
They are derivatives of fluorene-$9$-carboxylic acid and are known to interfere with various physiological processes such as cell division, cell enlargement, and organ differentiation.

(A) The red-far red light response is a classic photomorphogenic response in plants.
This response is mediated by a pigment protein known as Phytochrome.
Phytochrome exists in two interconvertible forms: $P_r$ (which absorbs red light) and $P_{fr}$ (which absorbs far-red light).
When $P_r$ absorbs red light,it converts to $P_{fr}$,and when $P_{fr}$ absorbs far-red light,it converts back to $P_r$.

(B) Phytohormones,also known as plant growth regulators (PGRs),are chemical substances produced naturally by plants. They are synthesized in small quantities in various parts of the plant and are transported to other regions where they influence physiological processes such as growth,development,differentiation,and responses to environmental stimuli. Therefore,option $(b)$ is the most comprehensive and accurate definition.

(A) Phytohormones,also known as plant growth regulators $(PGRs)$,are chemical substances that are produced naturally in plants. They are organic compounds that regulate various physiological processes such as growth,development,and responses to environmental stimuli. These hormones control the entire life cycle of a plant,from seed germination to maturity,flowering,and senescence. Therefore,all the given options describe the functions of phytohormones,but the most comprehensive definition is that they are chemical substances that regulate growth and physiological processes throughout the plant's life cycle.

(D) Plant hormones,also known as phytohormones,are chemical substances produced by plants that act as regulators.
They influence various physiological processes such as growth,development,and movement within the plant.
Examples include $Auxins$,$Gibberellins$,$Cytokinins$,and $Abscisic$ $acid$.

(B) Plant hormones (phytohormones) are chemical substances produced in specific regions of the plant,such as shoot tips,root tips,or developing seeds.
Once synthesized,these hormones are transported from their site of synthesis to other target organs or tissues where they exert their physiological effects.
This transport is generally unidirectional,moving from the source (site of production) to the sink (site of action).

(D) The correct answer is $D$.
$PGRs$ (Plant Growth Regulators) are not divided into three groups based on their functions.
Instead,they are broadly classified into two main groups based on their physiological roles:
$1$. Plant Growth Promoters (e.g.,auxins,gibberellins,and cytokinins) which promote growth activities like cell division,cell enlargement,and pattern formation.
$2$. Plant Growth Inhibitors (e.g.,abscisic acid) which play a role in plant responses to wounds and stresses of biotic and abiotic origin,and are involved in various growth-inhibiting activities like dormancy and abscission.
Therefore,the statement that they are divided into three groups is incorrect.

(B) The correct matches are as follows:
$A$. $F. W. Went$ isolated $Auxin$ from the tips of oat seedlings.
$B$. $E. Kurosawa$ discovered $Gibberellic$ $acid$ $(GA)$ from the fungus $Gibberella$ $fujikuroi$.
$C$. $Skoog$ and $Miller$ identified and crystallized the cytokinesis-promoting active substance,$Kinetin$.
$D$. $Cousin$ confirmed the release of a volatile substance from ripened oranges that hastened the ripening of stored unripened bananas,which was later identified as $Ethylene$.
Therefore,the correct sequence is $A-3, B-2, C-1, D-4$.

(D) Plant growth regulators (PGRs) are small,simple molecules of diverse chemical composition. They are synthesized by plants in very small amounts and are responsible for regulating various physiological processes such as growth,development,and responses to environmental stimuli. Therefore,they are defined as chemical substances synthesized by the plant that regulate its physiological processes.

(N/A) Plant growth regulators (PGRs) are small,simple molecules of diverse chemical composition.
They can be indole compounds (e.g.,$IAA$),adenine derivatives (e.g.,$kinetin$),derivatives of carotenoids (e.g.,$abscisic$ $acid$),terpenes (e.g.,$gibberellic$ $acid$),or gases (e.g.,$ethylene$).
Key characteristics of PGRs include:
$1$. They are synthesized in various parts of the plant and can be transported to other regions.
$2$. They act in very small concentrations to regulate physiological processes.
$3$. They control growth,differentiation,and development within the plant.
$4$. They can act synergistically or antagonistically to influence plant responses to environmental stimuli.

(N/A) The discovery of plant growth regulators (PGRs) is a result of various observations and experiments:
$1$. Auxins: Charles Darwin and his son Francis Darwin observed that the coleoptiles of canary grass responded to unilateral illumination by growing towards the light source (phototropism). This led to the isolation of Auxin by $F$.$W$. Went from tips of oat seedlings.
$2$. Gibberellins: $E$. Kurosawa reported the appearance of symptoms of 'bakanae' (foolish seedling) disease in rice seedlings caused by the fungus Gibberella fujikuroi. The active substance was later identified as Gibberellic Acid.
$3$. Cytokinins: $F$. Skoog and Miller identified that the cytokinin (kinetin) was a modified form of adenine,which promotes cell division in tobacco pith culture.
$4$. Ethylene: $E$. Cousins confirmed the release of a volatile substance from ripened oranges that hastened the ripening of stored unripened bananas.
$5$. Abscisic Acid $(ABA)$: Three independent researchers reported the purification and chemical characterization of three different kinds of inhibitors: Inhibitor-$B$,Abscisin $II$,and Dormin. All three were later proven to be chemically identical and named Abscisic Acid.

(B) $1$. Plant hormones,also known as plant growth regulators (PGRs),are chemical substances that regulate growth and development.
$2$. $A$ key peculiarity of their transport is that they are transported throughout the plant body,but in very small amounts.
$3$. Unlike nutrients which move in bulk,hormones often exhibit polar transport (unidirectional movement from the source to the sink).
$4$. When a plant part undergoes senescence,nutrients are withdrawn from those regions and moved to the growing parts,and hormones play a regulatory role in this redistribution process.

(N/A) In plants,hormones are synthesized in various tissues such as shoot tips,root tips,meristematic tissues,developing leaves,and apical buds.
Hormones are translocated to the site of activity through the vascular tissues,specifically the $xylem$ and $phloem$.

(D) Plant growth regulators $(PGRs)$ are chemical compounds that influence the growth and development of plants. They are also known as plant hormones,plant growth substances,or phytohormones. Therefore,all the given options are correct.

(A) $(i)$ Generally,plant hormones are produced by many parts of a plant,not just a single site.
$(ii)$ $A$ single plant hormone can produce many different physiological effects depending on the target tissue.
$(iii)$ Most plant hormones like $ABA$,auxins,and $GA$ are acidic in nature,not basic.
$(iv)$ Therefore,the correct statement is that they are produced from many parts of the plant.

(A) Plant growth regulators $(PGRs)$ are small,simple molecules of diverse chemical composition. They include compounds like indole compounds (e.g.,$IAA$),adenine derivatives (e.g.,$kinetin$),derivatives of carotenoids (e.g.,$ABA$),terpenes (e.g.,$GA_3$),and gases (e.g.,$ethylene$). Since they belong to different chemical classes,they are described as having different chemical compositions.

(N/A) The plant growth regulators $(PGRs)$ are small,simple molecules of diverse chemical composition.
They can be indole compounds (indole-$3$-acetic acid,$IAA$); adenine derivatives ($N^{6}$-furfurylamino purine,kinetin); derivatives of carotenoids (abscisic acid,$ABA$); terpenes (gibberellic acid,$GA_{3}$); or gases (ethylene,$C_{2}H_{4}$).
Plant growth regulators are variously described as plant growth substances,plant hormones,or phytohormones in literature.
Types of $PGRs$:
The $PGRs$ can be broadly divided into two groups based on their functions in a living plant body:
$1$. Plant Growth Promoters: These are involved in growth-promoting activities,such as cell division,cell enlargement,pattern formation,tropic growth,flowering,fruiting,and seed formation. Examples include auxins,gibberellins,and cytokinins.
$2$. Plant Growth Inhibitors: The $PGRs$ of this group play an important role in plant responses to wounds and stresses of biotic and abiotic origin. They are also involved in various growth-inhibiting activities such as dormancy and abscission. Abscisic acid $(ABA)$ belongs to this group.
Note: The gaseous $PGR$,ethylene,could fit into either of the groups,but it is largely an inhibitor of growth activities.

(N/A) The discovery of all five major groups of plant growth regulators occurred largely by accident.
Discovery of Auxin:
This was the first growth hormone to be discovered. Observations of canary grass coleoptiles showed they responded to unilateral illumination by growing towards the light source (a phenomenon known as phototropism). After a series of experiments,it was concluded that the coleoptile tip was the site of production of a transmittable influence that caused the bending of the entire coleoptile. The first $PGR$ in the auxin group was isolated by $F.W. Went$ in $1928$ from the coleoptile tips of oat seedlings.
Discovery of Gibberellins:
In the early $20^{th}$ century,the 'bakane' (foolish seedling) disease of rice was reported to be caused by a fungal pathogen,$Gibberella$ $fujikuroi$. Symptoms included elongated stems and little or no grain production,leading to weak plants. It was later identified that the active substance was gibberellic acid. The Japanese plant pathologist $E. Kurosawa$ reported that uninfected rice seedlings developed these symptoms when treated with sterile filtrates of the fungus.
Discovery of Cytokinins:
$F. Skoog$ and his co-workers,while studying the nutritional requirements of tissue culture derived from tobacco stem internodes,observed that the callus (a mass of undifferentiated cells) proliferated only when the nutrient medium was supplemented with extracts of vascular tissues,yeast,coconut milk,or $DNA$. It was later found that the active substance was a modified form of adenine,which was crystallized and identified as kinetin. Compounds exhibiting kinetin-like properties were termed cytokinins.
Discovery of Abscisic Acid:
During the mid-$1960s$,three independent researchers reported the purification and chemical characterization of three different inhibitors: inhibitor-$B$,abscission $II$,and dormin. Later,all three were proven to be chemically identical and were named Abscisic Acid $(ABA)$.
Discovery of Ethylene:
$Cousins$ $(1910)$ confirmed the release of a volatile substance from ripened oranges that enhanced the ripening of stored unripened bananas. This volatile substance was later identified as the gaseous plant growth regulator,ethylene.

(N/A) $PGR$ (Plant Growth Regulators) play a vital role in every phase of plant growth,differentiation,and development.
These roles can be complementary or antagonistic,and they may act individually or synergistically.
In many physiological events,such as seed or bud dormancy,abscission,senescence,and apical dominance,multiple $PGRs$ interact to regulate the process.
$PGRs$ represent a form of intrinsic control within the plant.
Along with genomic control and extrinsic factors,they are essential for regulating plant growth and development.
Many extrinsic factors,such as temperature and light,influence plant growth and development by modulating the activity of $PGRs$.
Examples of such processes include vernalization,flowering,dormancy,seed germination,and plant movements.

(N/A) $F. Skoog$ and his co-workers,while studying the nutritional requirements of tissue culture derived from the internodal segments of tobacco stems,observed that the internodal segments (a mass of undifferentiated cells called callus) proliferated only when the nutrient medium containing auxin was supplemented with extracts of vascular tissues,yeast,coconut milk (liquid endosperm of coconut),or $DNA$.
$\Rightarrow$ It was later found that the active substance was a modified form of adenine,which was crystallized and identified as kinetin.
Further,the compounds that exhibited kinetin-like properties were termed as cytokinins.

(N/A) Plant growth regulators (PGRs) are small,simple molecules with diverse chemical compositions. They are specific organic compounds synthesized by plants that act as chemical messengers to regulate various physiological processes,including growth,development,and responses to environmental stimuli. Examples include auxins,gibberellins,cytokinins,abscisic acid,and ethylene.

(D) Plant growth regulators (PGRs) are small,simple molecules of diverse chemical composition. They are also referred to as plant growth substances,plant hormones,or phytohormones. These chemical compounds play a crucial role in regulating various physiological processes in plants,such as growth,development,and response to environmental stimuli. Therefore,all the given options are correct.

(A) Charles Darwin and his son Francis Darwin observed that the coleoptiles of canary grass $(Phalaris \text{ canariensis})$ respond to unilateral illumination by growing towards the light source (phototropism). They concluded that the tip of the coleoptile was the site of transmittable influence that caused the bending of the entire coleoptile.

(B) The correct matches are as follows:
$A$. Auxin: Charles Darwin and Francis Darwin observed the coleoptiles of canary grass $(IV)$.
$B$. Gibberellins: $E$. Kurosawa reported the appearance of symptoms of 'bakanae' disease in rice seedlings $(III)$.
$C$. Ethylene: $H$.$H$. Cousins confirmed the release of a volatile substance from ripened oranges that hastened the ripening of stored unripened bananas $(II)$.
$D$. Cytokinin: Miller et al. identified and crystallized the cytokinesis-promoting active substance that they termed kinetin $(I)$.
Therefore,the correct sequence is $A-IV, B-III, C-II, D-I$.

(D) The term $hormone$ was first coined by $E.H. Starling$ in $1906$ in the context of animal physiology.
These chemical messengers regulate various physiological processes in organisms.
In plants,such regulatory substances are referred to as phytohormones or plant growth regulators.