Question

Which plant hormone of the following is used to initiate flowering and for synchronizing fruit set in pineapples?
(a)Kinetin
(b)Gibberellin
(c)ABA
(d)Ethylene

Answer 1

Hint: Plant hormones are molecules required for the enhanced growth of the plants or specific parts of it. They also help in breaking seed dormancy, growth of fruits or flowers, lengthening of roots or shoots, etc. The hormone required for the given processes is a simple molecule and gaseous in nature.

Complete answer: - Plant hormones, or plant growth regulators (PGR) are simple organic molecules involved in promoting or regulating the growth of plants.
- Ethylene is a simple molecule existing in gaseous form that promotes flowering and synchronizing fruit set in pineapples. It is produced in large quantities by plant tissues undergoing senescence and ripening fruits.
- Ethylene is also used to induce flowering in mango and ripening of tomatoes and apples. This is mainly because it promotes senescence and ripening.
- Other actions of ethylene include breaking of seed and bud dormancy, initiation of germination in peanut seeds and sprouting of potato tubers, rapid internode/petiole elongation in deepwater rice plants, and root growth and root hair formation.

Additional Information: - Kinetin is a form of cytokinin that is a hormone promoting cell division in tissues. It does not naturally occur in plants. Cytokinins help in forming new leaves, lateral shoot growth, chloroplast in leaves, and adventitious shoot formation. Treatment with proportions of auxin and cytokinin promotes root or shoot differentiation in plant tissue culture.
- Gibberellins are a group of growth-promoting acids. They are naturally present in germinating seeds, young embryos, and leaf buds. They are mainly used for an increase in internode lengths.
- ABA or Abscisic Acid is a growth inhibitor. From its name, it has a role in maintaining abscission and dormancy. ABA biosynthesis occurs in the chloroplast and cytoplasm of the cell. It is a growth inhibitor, especially seed germination. ABA additionally stimulates the closure of stomata in case of water stress and increases the tolerance of plants to various kinds of stresses. Hence, it is also known as a stress hormone.

So, the correct answer is ‘Ethylene’.

Note: - The major PGRs are tryptophan-derived indole compounds, derivatives of adenine and carotenoids, terpenes, or gases.
- Auxin was the first plant hormone to be discovered.
- The most widely used source of ethylene is ethephon/ethrel, an aqueous solution that gets broken down into ethylene, phosphoric acid, and chloride ions.