Question

Spraying sugarcane with gibberellin increases the yield by as much as 20 tonnes per acre. GA performs it by
(a) Improving quality of fruit
(b) Increasing sugar content
(c) Internodal elongation
(d) Delaying senescence

Answer 1

Hint: Gibberellins are plant growth hormones which enhance the longitudinal growth of stem when applied to intact plants. They do not enhance the growth of isolated plant parts. The presence of meristematic cells is necessary for gibberellin induced growth in length. Gibberellins cause the extraordinary elongation of stems and leaf sheath in intact plants. Studies have shown that external supply of GA to dwarf plants causes rapid elongation.

Complete step by step answer:
Elongation of stem helps in Internodal elongation which increases the yield of sugarcane. The elongation of the stem is due to cell division and cell elongation, induced by gibberellic acid. One of the most striking effects of gibberellin is the reversal of dwarfism in many genetically dwarf plants. Rosette plants of sugar beet, when treated with gibberellins, undergo marked longitudinal axial growth. Extensive studies indicated that the dwarf plants have very low GA level which appears to account for the dwarf habit. Thus, the external supply of GA to such plants causes rapid elongation. Embryos, young apical leaves, buds, and root tips are the active centers of gibberellin synthesis. Gibberellins move away from the sites of their synthesis in a nonpolar manner. i.e. both upward and downward. Long distance distribution occurs through both xylem transport and phloem transport. Gibberellins promote cell enlargement in the presence of auxins. They also promote fruit growth and induce parthenocarpy.
So, the answer is ‘Internodal elongation'.

Additional Information:
- Yabuta and Sumuki successfully isolated gibberellic acid in crystalline form from the culture filtrate of the fungus Gibberella fujikuroi.
- Now more than 830 different gibberellins are known. They are chemically gibberellic acid.
- Gibberellins helps to break seed dormancy, bud dormancy, fruit dormancy and promote seed germination.

Note:
- Gibberellic acid, ethephon, Glyco phosine, etc. are some synthetic Gibberellins.
- Gibberellic acid is used to increase fruit setting in pears, to minimize the loss of apple yield due to frost damage, to increase the berry size of seedless grapes.
- Glyco phosphine is applied to hasten the ripening of sugarcane. Ethephon is applied to increase latex flow in rubber plants.