Correct option is D
The correct answer is: Option 4: A and C
Explanation:
A. Gibberellins are ubiquitous in plants and are also present in several fungi.
This statement is correct.
Gibberellins (GAs) are plant hormones that regulate growth and development.
They are widely found in all plant species and also in several fungi, including Fusarium and Gibberella species.
These hormones play a role in seed germination, stem elongation, and flowering.
B. GA₁ is the most abundant gibberellin produced in the fungus Fusarium fujikuroi.
This statement is incorrect.
The fungus Fusarium fujikuroi is known for producing gibberellins, but the most abundant form it synthesizes is GA₃ (Gibberellic acid 3), not GA₁.
Fusarium fujikuroi was historically linked to the discovery of gibberellins because it causes "bakanae" disease (foolish seedling disease) in rice, leading to excessive growth.
C. The exogenous application of gibberellin, GA₃, stimulates dramatic stem elongation in the dwarf maize mutant but has little effect on the tall, wild-type plant.
This statement is correct.
Dwarf plants often lack functional gibberellin biosynthesis or signaling components.
When GA₃ (exogenous gibberellin) is applied to dwarf maize, it compensates for the plant’s deficiency and triggers stem elongation.
In contrast, tall wild-type plants already have sufficient endogenous gibberellins, so exogenous application has minimal impact.
D. The application of exogenous gibberellins causes upregulation of the GA20 oxidase and GA3 oxidase genes.
This statement is incorrect.
Gibberellins regulate their own biosynthesis via negative feedback.
Exogenous gibberellins generally lead to downregulation of GA biosynthesis genes such as GA20 oxidase and GA3 oxidase because the plant senses that sufficient gibberellins are present.
Instead, GA2 oxidase (which deactivates gibberellins) is upregulated in response to excess GA.
