Tag: plants: structure and function

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.

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.