Question

What is the precursor of the plant hormone gibberellin?

Answer 1

Hint: Gibberellins are the plant hormones that are involved in regulating the growth, and developmental processes like elongation of the stem, flowering, germination, enzyme induction etc. These are mainly acids that are produced in the plastids of the plants. They are transferred to the endoplasmic reticulum and further processed for use.

Complete answer:
To solve this question, we must know about the structure and how the gibberellins are produced.
Several types of Gibberellins are present in many plants and fungi. It was discovered by E. Kurosawa in 1926. It was seen that the bakanae disease was caused by Gibberella fujukuroi.

Gibberellins are the tetracyclic diterpenes that have an ent-gibberellin ring structure. They mostly have around 19 or 20 carbon atoms. The gibberellic acid is biosynthesised from geranyl diphosphate which is a C20 precursor for diterpenoids. The biosynthesis is carried out by the methylerythritol phosphate pathway in higher plants. The figure below shows the structure of gibberellin. These hormones are found in shoot, roots, leaves.

Additional information: The other plant hormone is ethylene- it promotes the ripening of the fruits. It is the most explored hormone. The other growth hormone in the plant is auxins- they are produced naturally by the plants and play a vital role in cell division. It is present in the root and shoot tips. This hormone is also responsible for the trophic movements of the plants.

Note: The best-known gibberellin is gibberellic acid which is a weak acid. Vitamin E and helminthosporol also exhibit gibberellin like activity. They can fasten the elongation of dwarf varieties to normal size further.