Cytokinin Questions in English

(C) Cytokinin is a plant hormone that stimulates cell division.
One of its significant functions is to delay senescence through the 'Richmond-Lang effect'.
It prevents the degradation of chlorophyll and maintains protein synthesis,which allows leaves to remain green for a longer period.

(B) In plant tissue culture,the balance between auxins and cytokinins is crucial for organogenesis. Cytokinins are specifically known for promoting cell division and are essential for shoot induction (caulogenesis) in callus cultures. When the ratio of cytokinin to auxin is high,it promotes shoot development,whereas a high auxin to cytokinin ratio promotes root development.

(C) In plant tissue culture,the process of organogenesis is primarily regulated by the balance between two plant hormones: $Auxin$ and $Cytokinin$.
$1$. $A$ high $Auxin : Cytokinin$ ratio promotes root differentiation.
$2$. $A$ high $Cytokinin : Auxin$ ratio promotes shoot differentiation.
Therefore,shoot differentiation is controlled by a high $Cytokinin : Auxin$ ratio.

(A) The yellowing of leaves and poor development in pulse crops often indicate a deficiency in essential nutrients or hormonal imbalances. Cytokinins are plant hormones that promote cell division and delay senescence (aging) of leaves. By applying cytokinins,the plant can maintain green,healthy leaves for a longer period. Supplementing this with small amounts of nitrogenous fertilizer provides the necessary building blocks for protein and chlorophyll synthesis,which directly boosts the photosynthetic capacity and overall yield of the pulse crop.

(A) Cytokinins promote cell division and inhibit the degradative processes in detached leaves,thereby delaying senescence in intact leaves. The phenomenon of cytokinin-induced retardation of aging is known as the $Richmond-Lang$ Effect.

(D) Coconut water is a rich source of cytokinin.
Cytokinins are plant hormones that promote cell division (cytokinesis) and are typically found in areas of rapid growth and dividing tissues.
Because of this property,coconut water is widely used as a supplement in plant tissue culture media to stimulate cell division and growth.
Coconut water is essentially the liquid endosperm of the coconut seed.

(C) The plant hormone responsible for delaying senescence (aging) in leaves and keeping plants evergreen is $Cytokinin$.
$Cytokinins$ promote cell division and delay the breakdown of chlorophyll and proteins in leaves.
By inhibiting the process of senescence,they help maintain the green color and vitality of plant tissues for a longer duration.
Therefore,$Cytokinins$ are essential for maintaining the evergreen nature of plants.

(C) The plant hormone discovered from the sperm of herring fish is $Cytokinin$.
Specifically,a compound named $Kinetin$ was isolated from autoclaved herring sperm $DNA$.
$Kinetin$ is a type of $Cytokinin$ that promotes cell division $(cytokinesis)$ in plants.
It was discovered by $Miller$ and $Skoog$ while studying the growth-promoting factors in plant tissue culture.

(N/A) Cytokinins are a class of plant growth substances (phytohormones) that promote cell division (cytokinesis). Their primary effects include:
$1$. Promotion of cell division: They play a crucial role in cytokinesis,especially in the presence of auxin.
$2$. Delay of senescence: Cytokinins help in delaying the aging process (senescence) in leaves and other organs by promoting nutrient mobilization.
$3$. Overcoming apical dominance: They promote the growth of lateral buds,thereby counteracting the effect of apical dominance caused by auxins.
$4$. Adventitious shoot formation: They are used in tissue culture to induce the formation of shoots from callus.
$5$. Chloroplast development: They promote the development of chloroplasts in leaves.

(N/A) $(1)$ Cytokinin stimulates cell division and cell expansion in plants. Furthermore,its effect reduces apical dominance and delays senescence (aging). It helps in the retention of chlorophyll in leaves,preventing them from turning yellow and falling off. Thus,it keeps the plant fresh and green,which is why it is called an evergreen hormone.
$(2)$ The phenomenon of growth depends on several factors. For instance,oxygen is essential for respiration. Water is necessary to maintain cell turgor pressure. An optimal temperature range of $28^{\circ}C$ to $30^{\circ}C$ is required. Light is essential for photosynthesis. Nutrients are required for the synthesis of protoplasm,and minerals are also indispensable. Thus,growth is regulated by multiple internal and external factors.

(N/A) To increase the life span of cut plants in a vase,the following methods can be used:
$1$. Recutting the stems: Cut the base of the stem at an angle under water. This prevents air embolisms (air bubbles) from entering the $xylem$ vessels,which would otherwise block the upward movement of water and nutrients.
$2$. Use of preservatives: Adding sugar (sucrose) provides an energy source for the cells,while adding a small amount of bleach or citric acid helps inhibit the growth of bacteria and fungi that can clog the $xylem$.
$3$. Application of phytohormones: Treating the cut plants with cytokinins can delay senescence (aging) by maintaining protein synthesis and chlorophyll levels in the leaves.

(B) The term 'Kinetin' was discovered and coined by $Skoog$ and $Miller$ during their research on plant tissue culture. It is a type of cytokinin that promotes cell division.

(A) In plant tissue culture,the ratio of phytohormones determines the differentiation of the callus.
Cytokinins are responsible for promoting shoot development and cell division (cytokinesis) in the callus.
While Auxins promote root development,a higher concentration of Cytokinin relative to Auxin induces shoot formation.

(B) Cytokinins are plant growth hormones that promote cell division (cytokinesis).
They are primarily synthesized in regions where rapid cell division occurs,such as root apices,developing shoot buds,and young fruits.
Since their primary function is to stimulate cell division,they are naturally produced in tissues that are actively and rapidly dividing.

(B) Senescence is the process of ageing which is caused by increased entropy,cellular breakdown,reduced anabolic process,and increased catabolic process.
Cytokinins are amino purine derivatives that promote cell division and delay senescence by controlling protein synthesis.

(D) The first cytokinin was discovered as kinetin,which is a modified form of adenine.
Kinetin does not occur naturally in plants.
Subsequent research for natural substances with cytokinin-like activity led to the isolation of zeatin from corn kernels and coconut milk.
Therefore,zeatin is a naturally occurring cytokinin,while kinetin is a synthetic form.

(A) Richmond and Lang $(1967)$ observed that the degradation of proteins and chlorophyll was delayed in the detached leaves of $Xanthium$ by the application of cytokinin. This effect of cytokinin in delaying senescence is known as the Richmond-Lang effect.

(A) In coconut,the endosperm is multicellular in the outer part and free nuclear in the centre (i.e.,liquid endosperm).
The endosperm of coconut contains the hormone cytokinin,which promotes cell division.

(D) Cytokinins are plant hormones that promote cell division (cytokinesis).
Their primary functions include the formation of new leaves,chloroplast formation in leaves,lateral shoot growth,and adventitious shoot formation.
However,rooting on stem cuttings is primarily promoted by auxins,not cytokinins.
Therefore,statement $V$ is not a function of cytokinin.

(A) Cytokinin is a plant growth regulator that plays a crucial role in delaying leaf senescence. It achieves this primarily by promoting nutrient mobilisation,which directs the flow of nutrients to the leaves,thereby maintaining their metabolic activity and delaying the aging process.

(D) $I.$ Correct: Cytokinins are synthesized primarily in root apices.
$II.$ Correct: Auxin promotes apical dominance,while cytokinin promotes lateral bud growth,showing an antagonistic effect.
$III.$ Correct: Kinetin was discovered from autoclaved herring sperm $DNA$.
$IV.$ Incorrect: Zeatin is a type of cytokinin,not an auxin.
$V.$ Incorrect: Zeatin was first isolated from corn kernels (maize) and coconut milk,not from herring.
Therefore,statements $IV$ and $V$ are incorrect.

(D) Apical dominance is the phenomenon where the main central stem of the plant grows more dominantly than the side stems. Auxin,produced in the apical bud,promotes this growth. Cytokinin is known to be antagonistic to auxin in this process,as it promotes the growth of lateral buds and helps overcome apical dominance.

(C) Cytokinin is basic in nature because it is a derivative of adenine (a purine base). In contrast,auxin,gibberellins,and abscisic acid are acidic in nature.

(B) The Richmond-Lang effect refers to the ability of cytokinins $(CK)$ to delay or postpone the process of senescence (aging) in plant tissues,such as detached leaves. By maintaining protein synthesis and chlorophyll content,cytokinins effectively slow down the degradation processes associated with aging.

(A) Cytokinins are plant hormones that promote cell division and delay the process of senescence (aging) in plant tissues. By inhibiting the breakdown of chlorophyll and proteins,cytokinins help maintain the freshness of vegetables and cut flowers,thereby increasing their shelf life.

(D) Cytokinins are known as anti-ageing hormones because they delay the senescence of plant parts.
This process occurs primarily through two mechanisms:
$1$. They promote the mobilisation of nutrients and resources from older parts to younger,developing parts of the plant.
$2$. They help in maintaining protein synthesis and preventing the degradation of chlorophyll and other essential cellular components,thereby delaying the ageing process.

(C) Cytokinins are known as anti-ageing hormones because they delay the process of senescence in plants.
They promote the mobilization of nutrients and help in delaying the breakdown of chlorophyll and proteins.
The Reason provided states that they increase the volume of mature cells to change osmotic potential,which is scientifically incorrect.
Therefore,the Assertion is correct,but the Reason is incorrect.

(C) The Assertion is correct because morphogenesis (organ formation) in plant tissue culture is regulated by the balance between cytokinin and auxin.
The Reason is incorrect because a higher cytokinin to auxin ratio promotes shoot initiation,whereas a higher auxin to cytokinin ratio promotes root initiation.
Therefore,the correct answer is that the Assertion is correct,but the Reason is incorrect.

(N/A) Cytokinins have specific effects on cytokinesis and were discovered as kinetin (a modified form of adenine,a purine) from autoclaved herring sperm $DNA$.
$\Rightarrow$ Kinetin does not occur naturally in plants.
$=$ The search for natural substances with cytokinin-like activities led to the isolation of zeatin from corn kernels and coconut milk.
- Since the discovery of zeatin,several naturally occurring cytokinins and some synthetic compounds with cell division-promoting activity have been identified.
$\rightarrow$ Natural cytokinins are synthesized in regions where rapid cell division occurs,for example,root apices,developing shoot buds,and young fruits.
- They help in the production of new leaves,chloroplasts in leaves,lateral shoot growth,and adventitious shoot formation.
$=$ Cytokinins help overcome apical dominance.
- They promote nutrient mobilization,which helps in the delay of leaf senescence.

(N/A) Cytokinins are a class of plant growth substances (phytohormones) that promote cell division,or cytokinesis,in plant roots and shoots. They were discovered by Miller et al. during the investigation of cell division-promoting activity in degraded $DNA$ preparations. They help in producing new leaves,lateral shoot growth,and adventitious shoot formation. They also help in delaying leaf senescence.

(C) The term 'kinetin' was coined by $Skoog$ and $Miller$ during their research on plant growth regulators. They identified kinetin as a modified form of adenine (a purine) from autoclaved herring sperm $DNA$. It was the first cytokinin to be discovered,which promotes cell division.

(D) Kinetin is a synthetic cytokinin. It is a derivative of adenine ($6$-furfurylaminopurine) and was discovered from autoclaved herring sperm $DNA$. It does not occur naturally in plants. Other options like Abscisic acid,Gibberellins,and Auxin are naturally occurring plant growth regulators.

(D) Cytokinins are plant hormones that promote cell division (cytokinesis) in plant roots and shoots.
They are also involved in the regulation of xylem differentiation,lateral shoot growth,and the delay of leaf senescence.
Therefore,the correct option is $D$.

(C) Cytokinins were discovered by Miller et al. $(1955)$ as a kinetin (a modified form of adenine,a purine) from autoclaved herring sperm $DNA$.
Kinetin does not occur naturally in plants,but it led to the discovery of other natural substances with cytokinin-like activities,such as zeatin,which was isolated from corn kernels and coconut milk.

(A) Cytokinins are plant growth regulators that play a crucial role in delaying leaf senescence (aging).
They promote the synthesis of chlorophyll and prevent its degradation,thereby keeping leaves green for a longer period.
This phenomenon is known as the Richmond-Lang effect.

(D) Zeatin is a type of cytokinin, which is a plant growth hormone.
It was first isolated from corn kernels $(Zea \, mays)$.
However, the term 'cytokinin' was coined after the discovery of kinetin, which was isolated from autoclaved herring sperm $DNA$.
Coconut milk is also a rich source of cytokinins.
Therefore, zeatin and other cytokinin-like substances have been obtained from these various sources.

(B) Plant growth regulators are chemical substances that control growth and development in plants.
Cytokinins are a class of plant growth substances that promote cell division,or cytokinesis,in plant roots and shoots.
Chemically,cytokinins are adenine derivatives (specifically $N^6$-substituted adenine derivatives).
Examples include zeatin,which was isolated from corn kernels and coconut milk.
Therefore,the correct answer is $B$.

(D) Cytokinins are a class of plant growth substances (phytohormones) that promote cell division or cytokinesis in plant roots and shoots.
One of the most significant physiological effects of cytokinins is their ability to promote nutrient mobilization.
This mobilization of nutrients helps in delaying leaf senescence (the aging process of leaves) by maintaining the synthesis of proteins and chlorophyll,thereby keeping the leaves green for a longer period.
This phenomenon is also known as the Richmond-Lang effect.

(B) Natural $Cytokinin$ are reported from plants like $Banana$ flowers,apple and tomato fruits,coconut milk,etc.

(B) Apical dominance is the phenomenon where the main central stem of the plant grows more dominantly than the side stems,primarily due to the presence of $Auxin$ at the shoot apex.
$Cytokinins$ are plant hormones that promote cell division and are known to counteract apical dominance by stimulating the growth of lateral buds.
Therefore,when $Cytokinins$ are applied to the lateral buds,they overcome the inhibitory effect of $Auxin$ produced by the apical bud,allowing the lateral branches to grow.

(D) Cytokinins are known to promote cell division and growth in plants.
They are specifically responsible for inducing $RNA$ synthesis and protein synthesis.
Additionally,they help in the formation of interfasicular cambium and are involved in reversing apical dominance.

(C) Cytokinins are plant hormones that promote cell division,delay senescence,and help in the formation of new leaves and lateral shoot growth.
Option $A$ is incorrect because cytokinins promote cell division,while auxins and gibberellins are more associated with cell enlargement.
Option $B$ is incorrect because cytokinins help overcome apical dominance by promoting the growth of lateral buds.
Option $C$ is the correct answer because cytokinins delay senescence,whereas senescence is hastened by hormones like $ABA$ (Abscisic acid) and ethylene.
Option $D$ is incorrect because cytokinins are involved in the formation of interfascicular cambium.

(B) The $Richmond-Lang$ effect is concerned with the delay in senescence or the retardation of aging by the application of the plant growth regulator $Cytokinins$.
It checks the disappearance of chlorophylls and the degradation of protein synthesis in leaves,thereby maintaining the greenness and metabolic activity of the leaf tissue for a longer period.

(B) During the secondary growth of plants,the formation and activity of the interfascicular cambium are promoted by Cytokinins. Cytokinins stimulate cell division in the cambial cells,which leads to the production of secondary xylem and secondary phloem,thereby increasing the girth of the stem.

(B) Cytokinins are plant hormones that promote cell division and are well-known for their role in delaying senescence in leaves and other plant organs.
They achieve this by mobilizing nutrients and maintaining chlorophyll content,which prevents the breakdown of cellular components associated with aging.
Abscisic acid promotes senescence,Ethylene accelerates fruit ripening and senescence,and Gibberellins are primarily involved in stem elongation and seed germination.

(A) The Richmond-Lang effect refers to the phenomenon where the application of cytokinin delays the onset of senescence (aging) in detached leaves or plant tissues.
Cytokinins promote cell division and delay the degradation of chlorophyll and proteins,thereby maintaining the greenness and metabolic activity of the leaves for a longer period.
This effect was first demonstrated by $A$. Richmond and $A$. Lang in $1957$ using Xanthium leaves.

(B) The correct answer is $B$ (cytokinin).
Cytokinins are plant hormones that promote cell division and delay the process of senescence (aging) in plant tissues.
By spraying perishable vegetables with a cytokinin solution,the degradation of chlorophyll and proteins is slowed down,thereby maintaining their freshness and extending their shelf life.