Abscisic acid - class-XI

Abscisic acid is a phytohormone critical for plant growth and development and plays an important role in integrating various stress signals and controlling downstream stress responses. Plants have to adjust ABA levels constantly in response to changing physiological and environmental conditions. ABA causes the closure of stomata. It thus helps in reducing the rate of transpiration.

Abscisic acid is also called as abscism. It is a plant hormone which has carotenoid as precursor. ABA functions in many plant developmental processes, including bud dormancy. ABA is an isoprenoid plant hormone, which is synthesized in the plastidal 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway, unlike the structurally related sesquiterpenes, which are formed from the mevalonic acid-derived precursor farnesyl diphosphate, the C15 backbone of ABA is formed after cleavage of C40 carotenoids in MEP.

Abscisic acid is anti-transpirant hormone. It stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kind of stresses. It is also called stress hormone.

A substance that induces dormancy in seed is ABA. Abscisic acid (ABA), also known as abscisin II and dormin, is an isoprenoid plant hormone. ABA functions in many plant developmental processes, including bud dormancy. It is responsible for seed dormancy by inhibiting cell growth inhibits seed germination.

Abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy. But like other PGRs, it also has other wide ranging effects on plant growth and development. It acts as a general plant growth inhibitor and an inhibitor of plant metabolism. ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses.Therefore, it is also called the stress hormone. ABA plays an important role in seed development, maturation and dormancy. By inducing dormancy, ABA helps seeds to withstand desiccation and other factors unfavourable for growth. In most situations, ABA acts as an antagonist to gibberellins.

Despite its name, abscisic acid does not induce abscission in most plants. Instead, abscisic acid is involved in a plants response to stress and in seed dormancy, a temporary state of arrested physiological activity. As an environmental stress hormone, abscisic acid particularly promotes changes in plant tissues that are water stressed.

Deciduous plants shed leaves in autumn. The shedding of leaves is a controlled and orderly process preceded by the formation of abscission layer at the base of leaf or fruit.

Abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy. It is the hormone believed to be responsible for controlled abscission of mature leaves and fruits from plants. But like other PGRs, it also has other wide ranging effects on plant growth and development. It acts as a general plant growth inhibitor and an inhibitor of plant metabolism. ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called as the stress hormone.

Abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy. But like other PGRs, it also has other wide ranging effects on plant growth and development. It acts as a general plant growth inhibitor and an inhibitor of plant metabolism. ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases  the tolerance of plants to various kinds of stresses. Therefore, it is also called as the stress hormone. ABA plays an important role in seed development, maturation and dormancy. By inducing dormancy, ABA helps seeds to withstand desiccation and other factors unfavourable for growth. In most situations, ABA acts as an antagonist to gibberellins.

Abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy. But like other PGRs, it also has other wide ranging effects on plant growth and development. It acts as a general plant growth inhibitor and an inhibitor of plant metabolism. ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called as the stress hormone. ABA plays an important role in seed development, maturation and dormancy. By inducing dormancy, ABA helps seeds to withstand desiccation and other factors unfavourable for growth. In most situations, ABA acts as an antagonist to gibberellins.

Abscisic acid (ABA) is a well-known plant hormone that acts primarily as a growth inhibitor, promoting seed dormancy and stomatal closure. Cytokinin, Gibberellin, and Auxin are primarily growth-promoting hormones.

Auxin is the plant growth hormone that promotes lengthening and coordinates with other growth hormones to regulate growth; it also causes apical dominance. Cytokinin is the plant growth hormone that promotes cell division in shoot apical meristem and differentiation in root apical meristem. It works antagonistically to auxin to balance the growth with development in the shoot and root apex. Gibberellins are responsible for stem elongation, breaking seed dormancy, mobilization of endosperm reserves as well as regulate sex determination, flower initiation and fruit set. Abscisic acid is a plant growth hormone involved in seed dormancy by suppressing seed germination and growth as well as in responses of plants to stress. This makes option D correct. 

Diffusion of CO$ _2$ into the leaf is decreased due to the closure of stomata and reduces the transpiration, which is done by antitranspirants.

Abscisic acid (ABA) induces dormancy. Robinson and Warming (1964), isolated a substance responsible for dormancy in Acer pseudoplatanus, and named it as dormin. This hormone was similar to abscission It is a naturally occurring hormone that is present in all vascular plants and some mosses but is not present in bacteria, algae fungi and liverworts. This hormone is responsible for dormancy.

By the end of summer, the leaves may be damaged by insects, disease or general wear and tear and ready for renewal. They are equipped to self-destruct. At the point where the leaf stem meets twig or branch is an array of cells called the abscission layer. As autumn days shorten, this layer begins to choke off the veins that move water into the leaf and food into the tree. Once the leaf is completely choked off, the layer becomes dry and flakey and, through decomposition, detaches the leaf from the tree.

IAA, NAA - are several forms of auxin hormone which promotes plant growth. At the same time, GA is gibberellic acid which initiates shoot elongation. ABA is abscissic acid which is an inhibiting hormone which causes dormancy and also inhibits the longitudinal growth of plant.

ABA is an inhibiting hormone which helps in the closure of stomata. It thus helps in control of transpiration. Whereas cytokinin promotes the opening of stomatal pore. It also initiates mitotic cell divisions.

Auxin plant hormone induces apical dominance. Apical dominance is the growth of the shoot apex of plant. It increases the height of the plant.
Cytokinins were first discovered in 1955 as promoters of cell division in the DNA of Herring sperm. Since, that discovery many different compound with cytokinin activity have been discovered, both natural and synthetic (diphenylurea).
Gibberellin induces the synthesis of $\alpha$-amylase in the aleurone layers. GAs are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction and leaf and fruit senescence.
Epinasty is the downward bending of a leaf or other plant part, resulting from greater growth of the upper side than of the lower side. Ethylene is the phytohormone which promotes epinastic movement in plants. It also promotes early ripening of fruits.

The synthesis of ABA is stimulated by drought, water logging and other adverse environmental condition. Therefore, it is also called as stress hormone. It is also called as 'growth inhibitor hormone', because it causes inhibition of seed germination, flowering and so on.

Ethylene hormone in plants helps in ripening of fruits. Abscisic acid is known for its inhibiting nature in growth. It causes bud dormancy in several plants. It also causes closure of stomata to minimize the loss of water by transpiration.

ABA is a plant hormone which is inhibiting in nature. It causes the closure of stomata, in order to reduce the rate of transpiration and the loss of water thereby. It is also well known for its dormant activity. ABA promotes early aging in the plant and also inhibits flowering, fruiting, germination, etc. 

Human urine - auxin. Human urine commonly shows the presence of Indole acetic acid, compound having similar properties to that of auxin.It was first discovered in 1931 by Kogl and Haagen Smit, five years earlier the discovery of auxins.
Gibberella fujikori - Gibberellin. G.fujikori is a fungal plant pathogen. It causes bakane disease in rice seedlings, by overloading them with the phytohormone; gibberellin as its own metabolic product.
Herring fish DNA - cytokinin. Cytokinins were first discovered in 1955 as promoters of cell division in the DNA of Herring sperm. Since, that discovery many different compound with cytokinin activity have been discovered, both natural and synthetic (diphenyurea).
Ripening fruits - ethylene. Ethylene is the only phytohormone present in gaseous state. It helps in inducing early ripening when sprayed to fruits.
Aged leaves of plants - ABA. Abscissic acid promotes the early aging of leaves, also called as senescence. Aging, dormancy of buds, inducing stomatal closure, inhibiting fruit ripening, etc, are the functions of ABA.

Senescence is a programmed developmental process. Leaf abscission is a classic example of programmed cell death and senescence in plants, allowing the plant to shed older or damaged leaves.

Antitranspirants are compounds applied to the leaves of plants to reduce transpiration. Some examples are phenylmercury acetate, abscisic acid (ABA), and aspirin (acetyl salicylic acid). ABA is a well-known antitranspirant.
Thus, the correct answer is an option (D). 

ABA is Abscisic acid. It is a plant hormone. In formation of winter buds, ABA is produced in terminal buds. It helps the conversion of the apical meristem into a dormant bud.

There are various plant hormones which act as growth regulators. Hormones like gibberellic acid (GA), Indoleacetic acid (IAA), a type of auxin, cytokinin (CK) are growth promoter. Hormones like Abscisic Acid (ABA), ethylene are growth inhibitor. These hormones accelerate abscission process.

 It inhibits root elongation, stem elongation and seed germination. It brings out the stomatal closure when soil water is insufficient to keep up with transpiration. It binds to receptor present on the guard cells and hence closes stomata.

Abscisic acid is a plant hormone. It is involved in various physiological processes of the plant. It acts as a plant growth inhibitor. It is also called as stress hormone as its concentration increases during stress condition. Under the unfavourable condition, it induces seed dormancy. When favourable condition returns, seed dormancy is broken. 

Stress hormone is a hormone produced during adverse environmental conditions. Abscisic acid (ABA) is called as stress hormone. Due to this hormone, plants respond to stresses conditions like cold, drought. It increases the tolerance of plants toward various stresses. It is found in high concentration in roots during drought and later translocated to leaves. It causes stomatal closure during water stress. It also promotes seed dormancy under adverse condition.

Auxin is a plant hormone that is involved in growth and development of plant. Kinetin, a type of cytokinin was isolated from autoclaved herring sperm DNA by Miller and Skoog. Gibberellin hormone was first isolated from fungus Gibberella fujikuroi. Ethylene is a gaseous hormone which helps in ripening process and hence also called as ripening hormone. ABA is responsible for abscission of leaves, fruits and flowers. Florigen is a flowering hormone that is responsible for flowering in certain plants.

Leaf abscission is a detachment or fall of older leaves.It occurs at the base of the petiole. During abscission, high synthesize of abscisic acid is observed along with decrease in the concentration of auxin. ABA loosens the cell wall and cells separate which ultimately leads to leaf abscission. 

Abscisic acid is a plant hormone. It causes abscission of leaves. It induces dormancy of seed under unfavorable condition. Gibberellin is a plant hormone that is an antagonist to the abscisic acid hormone. It regulates plant growth. It stimulates stem elongation, germination, flowering. it breaks the seed dormancy and initiates germination process. 

ABA helps seeds to withstand desiccation and other factors unfavorable for growth.

Abscisic acid inhibits seed germination and stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone.

The C₁₅ backbone of ABA is formed after cleavage of C_{40 Carotenoids.}

Seed dormancy is mainly caused by ABA. Dormancy allows seeds to tolerate desiccation and extremes of temperature better. Due to its action of inducing dormancy in seeds, buds etc. ABA is also called as dormin.

Abscissic acid regulates abscission (the shedding of leaves, flowers and fruits from the living plant) and dormancy. It acts as general plant growth inhibitor and also inhibit plant metabolism. It inhibits closure of stomata in epidermis, and increase tolerance of plant to various kinds of stresses, and therefore called as stress hormone.
ABA plays an important role in seed development, maturation and dormancy. By inducing dormancy, ABA helps seeds to withstand dessication and other factors favourable for growth.

Abscisic acid is the hormones also called as stress hormones as they function in stress conditions. They are also known as dormant as they induce dormancy in buds. It mostly induced bud dormancy at the start of the winter season. They are generally growth hormone which inhibits growth normally.

Dormancy is the period when the physiological activities of the plant slow down for some time. Abscisic acid is a stress hormone that is responsible for the protection of plants in drought conditions. They are generally growth inhibitors and are also called as dormants. They are mainly responsible for the bud dormancy at the time of winter season and also cause seed dormancy and protect it from desiccation.

Abscisic acid inhibits seed germination and stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone.

A plant will abscise apart either to discard a membrane that is no longer necessary, such as a leaf during autumn or a flower following fertilization or for the purpose of reproduction. Most deciduous plants drop their leaves by abscission before winter, whereas evergreen plants continuously abscise their leaves.