Cytokinin Questions in English

(D) The production of 'bonsai' plants involves restricting the growth of the plant to keep it small.
Drastic pruning of the root system is a key technique used for this purpose.
Roots are the primary site for the synthesis of cytokinins,which are plant hormones that promote cell division and shoot growth.
By pruning the roots,the plant's ability to synthesize and transport adequate amounts of cytokinins to the aerial parts is significantly reduced.
This deficiency of cytokinins leads to stunted growth and the characteristic small size of 'bonsai' plants.

(B) The differentiation of plant tissues in tissue culture is regulated by the balance between auxin and cytokinin.
High concentrations of cytokinin relative to auxin promote shoot development (caulogenesis).
Conversely,high concentrations of auxin relative to cytokinin promote root development (rhizogenesis).
Therefore,a high cytokinin to auxin ratio is responsible for shoot differentiation.

(A) Cytokinins are plant hormones that primarily promote cell division (cytokinesis) in plant roots and shoots.
They also play a crucial role in delaying leaf senescence (aging) by preventing the breakdown of chlorophyll and promoting nutrient mobilization.
Therefore,the induction of cell division and the delay in senescence are the primary functions of cytokinin.

(B) The correct answer is $B$. Kinin (a type of cytokinin) is a plant hormone that promotes cell division (cytokinesis) in plants. In the presence of kinin,the rate of mitotic cell division increases significantly,which is essential for plant growth and development.

(A) Cytokinins are known to promote cell division and delay the process of senescence in plants.
When green leaves are treated with a cytokinin solution,they retain their chlorophyll and remain green for a longer period.
This phenomenon,where cytokinins delay the aging or senescence of leaves,is specifically known as the $Richmond-Lang$ effect.

(C) The term "cytokinin" was proposed by $Letham$ in $1963$. This term is used to describe substances that promote cell division in plants. While $Skoog$ and $Miller$ discovered the first cytokinin $(kinetin)$, $Letham$ coined the specific term "cytokinin".

(C) Cytokinins are plant hormones that promote cell division and delay the process of senescence (aging) in plant tissues. By delaying senescence,cytokinins effectively prevent or delay the abscission of leaves,thereby preventing leaf fall.

(B) Cytokinins are plant hormones that promote cell division and delay the senescence of leaves.
They prevent the degradation of chlorophyll and proteins,thereby delaying the yellowing process,which is known as the $Richmond-Lang$ effect.

(C) Zeatin is a type of cytokinin. It was first isolated and identified from the endosperm of maize (corn) by Letham in $1963$. Therefore,the correct source is maize.

(B) The coconut milk factor is a substance that promotes cell division. It was identified as a cytokinin,specifically zeatin,which is present in the liquid endosperm of coconut. Therefore,the correct option is $B$.

(C) Zeatin is a naturally occurring cytokinin found in plants.
Cytokinins are a class of plant growth substances (phytohormones) that promote cell division,or cytokinesis,in plant roots and shoots.
Since it stimulates cell division and growth,it is classified as a growth promoter.

(A) Kinetin is a type of cytokinin,which is a plant growth regulator.
It is chemically identified as $N^6$-furfuryladenine.
It is a derivative of the purine base adenine,which bears a furfuryl group at the $N^6$ position.

(A) The discovery of $Cytokinins$ is linked to the observation by $Miller$ and $Skoog$ that the internodal segments of $Tobacco$ stems proliferated only when the nutrient medium was supplemented with one of the following: extracts of vascular tissues,yeast extract,coconut milk,or $DNA$. It was later identified that the active substance in autoclaved herring sperm $DNA$ was a kinetin,which is a form of $Cytokinin$.

(B) The phenomenon where cytokinins delay the senescence (aging) of leaves is known as the $Richmond-Lang$ effect. When an excised leaf is induced to form roots,the roots synthesize cytokinins. These cytokinins are transported to the leaf,where they prevent the breakdown of chlorophyll and delay the yellowing process (senescence). Therefore,cytokinins are responsible for retarding leaf aging.

(C) The cambial tissue of $Pinus radiata$ is known to contain high levels of cytokinin. Cytokinins are plant hormones that promote cell division (cytokinesis) in plant roots and shoots. In the context of cambial activity, cytokinins play a crucial role in stimulating the division of cambial cells, which leads to secondary growth in plants.

(B) Guttman $(1957)$ observed that treatment with Kinetin (a type of cytokinin) leads to a rapid increase in the synthesis of $RNA$ within the nuclei of onion root cells. Cytokinins are known to stimulate protein and $RNA$ synthesis,which is essential for cell division and growth.

(C) Kinetin is a type of cytokinin,which is a class of plant growth hormones. Cytokinins,including kinetin,are known to promote cell division and stimulate the synthesis of $RNA$ and proteins in plant cells. Therefore,$RNA$ formation is induced by kinetins.

(B) Cytokinin was first isolated and identified as zeatin from corn milk (maize endosperm) by Letham in $1963$. Skoog and Miller discovered the first cytokinin,kinetin,from autoclaved herring sperm $DNA$,but Letham is credited with the synthesis/isolation of the natural form from plant sources.

(C) Zeatin is a type of cytokinin,a plant growth hormone. It was isolated from corn kernels (Zea mays). The name 'zeatin' was coined by $D$.$S$. Letham in $1963$ after its discovery in the endosperm of maize.

(B) Cytokinins are plant growth regulators that are chemically derivatives of adenine,which are known as $N^6$-substituted aminopurines.
These compounds promote cell division in plants and are essential for growth and development.
Therefore,the correct classification for cytokinins is aminopurines.

(C) $6-$ furfuryl adenine is the chemical name for kinetin. Kinetin is a type of cytokinin,which is a class of plant growth hormones that promote cell division. It was discovered by Miller et al. from autoclaved herring sperm $DNA$.

(A) The Richmond-Lang effect refers to the ability of cytokinins to delay senescence in plant leaves by preventing the degradation of chlorophyll and promoting the retention of proteins and nucleic acids. Kinetin is a type of synthetic cytokinin. Therefore,Kinetin / $BA$ (Benzyladenine) is the correct answer.

(D) Cytokinins are plant hormones that promote cell division. Their primary physiological roles include delaying senescence (aging) in leaves and other plant organs,and promoting the mobilization of nutrients and solutes to various parts of the plant,which helps in maintaining the metabolic activity of the tissues. Therefore,option $D$ is the most comprehensive answer.

(A) Cytokinin stimulates cell division by promoting the transition of cells from the $G_2$ phase to the $M$-phase of the cell cycle.
It is essential for cytokinesis and is often used in tissue culture to induce shoot formation.

(C) Cytokinins are plant hormones that promote cell division and are essential for organogenesis (morphogenesis) in plant tissue culture.
In tissue culture,the ratio of cytokinin to auxin determines the development of shoots and roots.
$A$ higher concentration of cytokinin relative to auxin induces shoot formation,while a higher concentration of auxin relative to cytokinin induces root formation.

(B) Cytokinins are known to promote flowering in certain short-day plants $(SDP)$ such as $Lemna$ and $Wolffia$. While other hormones like gibberellins are primarily associated with long-day plants,cytokinins play a specific role in the floral induction of these particular species.

(B) $Cytokinins$ increase the shelf life of vegetables and cut flowers and keep them fresh for a longer time by preventing the deterioration of proteins and chlorophyll.

(C) Cytokinins are plant hormones that promote cell division and delay the process of senescence (aging) in leaves and other plant parts.
They prevent the degradation of chlorophyll,thereby maintaining the green color of leaves for a longer period.
This phenomenon is known as the $Richmond-Lang$ effect.

(C) Apical dominance is maintained by the presence of $Auxin$ (specifically $Indole$ $acetic$ $acid$) produced in the apical bud,which inhibits the growth of axillary buds.
When the apical bud is removed (pruning),the source of $Auxin$ is eliminated.
This removal allows the axillary buds to grow,as they become sensitized to $Cytokinin$,which promotes lateral bud development and branching.

(A) Cytokinins are plant hormones that promote cell division (cytokinesis).
They are primarily synthesized in the root apices (tips) where rapid cell division occurs.
From the roots,they are transported to other parts of the plant through the xylem.
While they are also found in developing fruits,young leaves,and seeds,the primary site of synthesis is the root system.

(A) Cytokinins are known to delay the senescence of plant organs by promoting nutrient mobilization and maintaining chlorophyll content. They help in preventing the breakdown of proteins and nucleic acids,thereby delaying the aging process in leaves and other plant parts.

(B) Cytokinins are essential for plant tissue culture. They are used to induce shoot formation (morphogenesis) in the cultured callus when the ratio of cytokinin to auxin is high.

(C) Cytokinins are known to delay senescence (Richmond-Lang effect). Senescence involves the loss of chlorophyll in mature leaves,leading to yellowing and abscission. Cytokinins help in maintaining the chlorophyll content and delaying this process.

(A) The growth of axillary buds is primarily regulated by the balance between auxin and cytokinin.
Auxin,produced in the apical meristem,inhibits the growth of axillary buds,a phenomenon known as apical dominance.
When the apical bud is removed or when the concentration of auxin decreases,the inhibitory effect is lifted.
Cytokinin promotes the growth of lateral or axillary buds.
Therefore,the activation of axillary buds,which contributes to the lateral growth or girth of the plant,is primarily driven by the increase in the ratio of cytokinin to auxin.

(D) Leaf senescence is inhibited by Cytokinin due to the Richmond-Lang effect. Cytokinin prevents the degradation of chlorophyll,proteins,and nucleic acids in leaves. It promotes the mobilization of nutrients and amino acids to the leaves,thereby delaying the aging process and maintaining metabolic activity.

(A) Kinetin is a synthetic cytokinin that promotes cell division. It accelerates the cell cycle by reducing the duration of the $G_1$ phase,which is a part of the interphase. By shortening the interphase,the cell reaches the mitotic phase more quickly,thereby increasing the overall rate of mitosis.

(A) The correct answer is $A$.
Premature yellowing of leaves (chlorosis) in pulse crops is often caused by a deficiency of nitrogen,as nitrogen is a critical component of chlorophyll,proteins,and nucleic acids.
Cytokinins are plant hormones that delay leaf senescence (aging) and promote cell division.
By applying a combination of cytokinins and nitrogenous fertilizers,the plant can maintain chlorophyll levels,delay senescence,and improve overall growth and seed yield.
While iron and magnesium are involved in chlorophyll synthesis,nitrogen deficiency is the most common cause of widespread chlorosis in pulse crops,making the combination of nitrogen and cytokinins the most effective treatment for maximizing yield.

(B) Apical dominance is a phenomenon where the main central stem of the plant grows more dominantly than the side stems,primarily due to the presence of auxins ($IAA$,$NAA$) at the shoot apex.
Cytokinins are plant hormones that promote cell division and are known to counteract the effect of apical dominance.
By applying cytokinins to the lateral buds,they can overcome the inhibitory effect of auxins,thereby promoting the growth of lateral branches.

(B) Coconut milk is a rich source of plant growth regulators,specifically cytokinins (such as zeatin).
In plant tissue culture,cytokinins are essential for promoting cell division and shoot differentiation.
Therefore,coconut milk is added to the culture medium to stimulate the growth and development of the explant.

(D) Cytokinins are a class of plant growth substances (phytohormones) that promote cell division,or cytokinesis,in plant roots and shoots.
They are known to help produce new cells by stimulating mitosis.
They also promote the formation of chloroplasts in leaves,which enhances photosynthesis.
Furthermore,cytokinins are essential for overcoming apical dominance,as they promote the growth of lateral buds.
Therefore,all the given options are correct functions of cytokinins.

(B) Skoog and Miller observed that the callus of tobacco stems proliferated only when,in addition to auxins,the nutrients medium was supplemented with one of the following: extracts of vascular tissues,yeast extract,coconut milk,or $DNA$.
They later identified and crystallized the cytokinesis-promoting active substance that they termed $Kinetin$.

(C) The incorrect statement is that cytokinins induce parthenocarpy in tomatoes.
Parthenocarpy (the development of fruit without fertilization) is primarily induced by auxins and gibberellins,not cytokinins.
Natural cytokinins are indeed synthesized in regions of rapid cell division such as root apices and developing shoot buds.
Kinetin is a synthetic cytokinin derived from adenine (a purine).
Cytokinins are well-known for delaying leaf senescence by promoting nutrient mobilization,which helps maintain the greenness of leaves for a longer period.

(D) $F$. Skoog and his co-workers observed that from the internodal segments of tobacco stems,the callus (a proliferation of parenchymatous cells) proliferated only if,in addition to auxin,the nutrients medium was supplemented with one of the following: extracts of vascular tissues,yeast extract,coconut milk,or $DNA$.
Later,Miller et al. identified and crystallized the cytokinesis-promoting active substance that they termed $Kinetin$.
$F$. Skoog is credited with the discovery of $Kinetin$,which is a type of cytokinin.

(A) Cytokinins are a class of plant growth substances (phytohormones) that promote cell division,or cytokinesis,in plant roots and shoots.
They are primarily synthesized in regions where rapid cell division occurs,such as root apices,developing shoot buds,and young fruits.
These hormones play a crucial role in delaying leaf senescence and promoting the growth of lateral buds.

(B) In plant tissue culture,the combination of auxin and cytokinin is essential for organogenesis. Auxin promotes root development,while cytokinin promotes shoot development. Skoog and Miller discovered that the addition of substances like yeast extract,coconut milk,or $DNA$ (which contain cytokinins) along with auxin significantly hastens cell division in callus tissue. Therefore,yeast extract is the correct additive to promote cell division in this context.

(C) 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. $(1955)$ and the first natural cytokinin identified was zeatin,isolated from corn kernels. While auxins like $IAA$ and $NAA$ promote cell enlargement and gibberellins promote stem elongation,cytokinins are specifically responsible for stimulating cell division.

(B) Cytokinins are plant hormones that promote cell division and delay the senescence (aging) of leaves. By applying cytokinin to the roots,the transport of nutrients to the leaves is maintained,which helps in preventing the breakdown of chlorophyll and keeps the leaves green for a longer period. This phenomenon is known as the Richmond-Lang effect.

(D) Cytokinins are plant hormones that promote cell division and delay the process of leaf senescence (aging).
They help in maintaining the chlorophyll content and protein synthesis in leaves for a longer duration,thereby preventing premature yellowing and shedding.
Abscisic acid,on the other hand,promotes senescence and abscission.
Therefore,the correct option is $D$.