Test: Plant Growth Regulators and Vernalisation - ACT MCQ

The stress hormone among the options provided is D: Abscisic acid.

- Abscisic acid regulates plant responses to environmental stress.
- It helps plants adapt to drought, salinity, cold temperatures, and other adverse conditions.
- This hormone inhibits plant growth to conserve energy during stressful periods.
- Abscisic acid also plays a role in seed dormancy and germination.
- Understanding its functions is crucial in agricultural practices for crop resilience.

Geocarpy refers to the ripening of fruits underground, In the case of ground nut, the young fruits are pushed into the soil as a result of post-fertilisation curvature of the stalk.

Ethylene is a gaseous hormone. It aids in ripening of climacteric fruits and dehiscence of dry fruits. Climacteric fruits are the fleshy fruits which show a sudden sharp rise of respiration rate at the time of ripening (respiratory climacteric). They are usually transported in green or unripe stage. Ethylene is used to induce artificial ripening of these fruits e.g., Apple, Mango, Banana, etc.

Cytokinins are a group of hormones that promote cell division in plant roots and shoots and the growth of buds. Coconut milk is at times used in some tissue culture medium as it is rich in cytokinins.

Stomata open in response to light. In response to drought stress, plants synthesize the hormone abscisic acid (ABA), which triggers closing of stomatal pores. Therefore it is a correct match.
Gibberellic acid promotes growth and does not have any effect on leaf fall. Therefore it is not a correct match.
Cytokinins (CK) are a class of plant growth substances (phytohormones) that promotecell division or cytokinesis, in plant roots and shoots. Therefore it is a correct match.
Auxin induces rapid elongation growth of higher plants. The mechanism of auxinaction in the elongation growth acts on the cell walls. Therefore it is a correct match.

Ratio of cytokinins to auxins controls differentiation. If both of these are present in equal quantities, the cells divide but fail to differentiate. If there is more cytokinin than auxin, shoot buds develop. If there is more auxin than cytokinin, roots develop.

• Abscisic acid (ABA) acts as a plant growth inhibitor and an inhibitor of plant metabolism.
• It has a role in regulating abscission and seed dormancy.
• ABA triggers the fall of mature leaves and fruits from plants.
• It accelerates senescence and inhibits seed germination.

• Apical Dominance: Apical dominance is the phenomenon where the terminal bud at the top of a plant suppresses the growth of lateral buds along the stem.


• Hormones Involved: Various plant hormones play a role in regulating apical dominance. One of the key hormones involved in this process is Indole-3-acetic acid (IAA).


• IAA: IAA is a type of auxin hormone that is produced in the apical meristem of the plant. It helps in promoting the growth of the apical bud and inhibiting the growth of lateral buds.


• Mechanism: The presence of high levels of IAA in the apical bud suppresses the growth of lateral buds by inhibiting their development. This leads to the dominance of the apical bud in controlling the growth of the plant.


• Role of Other Hormones: While IAA plays a significant role in apical dominance, other hormones such as cytokinins and strigolactones also interact with IAA to regulate the balance between apical and lateral bud growth.

Movements in nyctinasty plants are not related to auxin levels. 

Nyctinasty is a type of tactic movement of a plant where the movement of plants organs like leaves occur in response to day and light and thus known as sleep movements. (Circardian rhythm) Eg in case of Acasia torcuosa, the movement of leaves occur horizontal during the day and vertical during the night. 

It is the movement of the plants' organs like roots towards the soil, sunflower tracking towards the sun which are regulated by the Auxin levels. So, the correct option is'Nyctinasty leave movements'. 

Synthetic auxins are used as weedicides.

Option 1:

• IBA (indole butyric acid ) is natural auxin.
• It plays a major role in inducing adventitious roots in stem cuttings. 
• Therefore, this is the incorrect option.

Option 2:

• IAA (Indole acetic acid) is also natural auxin.
• It plays a major role in the elongation of plants and their development. 
• Therefore, this is the incorrect option.

Option 3:

• NAA (Naphthalene acetic acid) is a synthetic auxin.
• It initiates the rooting process.
• It is also useful in plant tissue culture. 
• Therefore, this is the incorrect option.

Option 4:

• 2, 4-D (2, 4-dichlorophenoxyacetic) is synthetic auxin. 
• 2,4-D is widely used to remove broad-leaved weeds or dicotyledonous weeds in cereal crops or monocotyledonous plants.
• It is also used to prepare weed-free lawns by gardeners. 

Therefore, the correct answer is option 4.

The hormones that delay senescence must decrease while the ones that speed up the aging process must increase. Cytokinins are one group of senescence delayers. These hormones are involved in cell growth, and high levels can help prevent senescence.

• Auxin refers to a group of plant hormones that regulate plant growth.
• Based on their origin, auxins can be divided into:
  • Natural Auxins - They occur naturally in the plant and affect physiological functions. E.g. - IAA, IBA.
  • Artificial Auxins - These are synthetically-derived chemical compounds that resemble IAA in biological activity. E.g. - NAA.
• Artificial auxins are widely used in horticultural practices, as weedicides, rooting agents and defoliating agents.

‘Foolish seedling’ of rice led to the discovery of GA.

Foolish seedling disease or Bakanae disease is a disease of rice seedlings, which was caused by a fungal pathogen . Kurosawa reported the appearance of symptoms of the disease in uninfected rice seedlings when they were treated with sterile filtrates of the fungus. The active substances were later identified as Gibberellic acid.