General Science Quiz: Plant Hormones and Economically Important Plants

Ethylene is the only gaseous plant hormone, and it raises the rate of respiration in climacteric fruits such as banana, mango and tomato, so a single ripe fruit speeds up the ripening of those around it; the compound ethephon releases ethylene and is used in orchards for uniform ripening.

It is produced when a plant faces drought, salinity or extreme temperature; it closes the stomata so that water is not lost, for which reason it is called an antitranspirant, and it induces dormancy in seeds and buds so that growth waits for better conditions.

Japanese rice plants attacked by this fungus grew abnormally tall and spindly, a condition called the foolish seedling or bakanae disease, and the substance responsible was isolated from the fungus and named gibberellin; gibberellic acid is the best known member of the group.

Auxin made at the shoot tip moves downwards and keeps the lateral buds below it inactive, which is why a gardener who nips off the tip of a hedge plant gets a bushy growth of side branches.

2,4-dichlorophenoxyacetic acid is a synthetic auxin, and when it is sprayed in a heavy dose it throws broad-leaved dicot weeds into uncontrolled growth that kills them, while narrow-leaved cereals such as wheat and rice are far less affected, so it clears weeds from a standing crop.

Saffron is made from the stigmas of the flower of Crocus sativus, and since each flower carries only three stigmas which must be picked by hand, the spice is the most expensive in the world; in India it is grown mainly in the Kashmir valley.

Quinine is an alkaloid extracted from the bark of trees of the genus Cinchona, native to South America and grown in India in the Nilgiris and in Darjeeling, and it was the standard treatment for malaria before synthetic drugs appeared.

Clove is the unopened flower bud of Syzygium aromaticum, picked before it blooms and dried, and it is grown in India chiefly in Kerala, Tamil Nadu and the Andaman and Nicobar Islands.

Jute is a bast or stem fibre taken from the inner bark of plants of the genus Corchorus, extracted by soaking the cut stems in water, a process called retting, and India and Bangladesh are the main producers.

Cytokinins promote cytokinesis, that is cell division; kinetin was the first of them to be identified, from the degraded DNA of herring sperm, and zeatin, the natural form, was obtained from maize grains.