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Which one of the plant growth regulators would you use if you are asked to :

(a) Induce rooting in a twig
(b) quickly ripen a fruit
(c) delay leaf senescence
(d) induce growth in axilliary buds
(e) ‘bolt’ a rosestte plant.
(f) induce immediate stomatal closure in leaves.


(a) Indole-3 butyric acid (Auxin)
(b) Ethylene
(c) Cytokinin
(d) Cytokinins
(e) Gibberellins
(f) Abscissic acid (ABA)
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What do you understand by photoperiodism and vernalisation ? Describe their significance.

(A) Photoperiodism . It is the response of plants to periods of day/night. The flowering in some plants depends not only on a combination of light and dark exposures but also their relative durations. The plants that need a longer duration for a period exceeding a well defined critical duration, while the short day plants must be exposed to light for a period less than this critical duration before the flowering is initiated in them.

Significance : Photoperiodism helps in studying the response of flowering in various crop plants with respect to the duration of exposure to light. It is the phenomenon which helps in flowering out of season.

(B) Vernalization : Vernalisation refers specially to the promotion of flowering by a
period of low temperature. It is the treatment of cold (3-15°C) to arrest vegetative growth and initiate flowering.

Significance of vernalization :

1. It shortens the vegetative phase.

2. It makes the plant resistant to cold and fungal pathogens.

3. It prevents precocious reproductive development late in the growing season, and enables the plant to have sufficient time to reach maturity.

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 “Both a short day plant and a long day plant can produce flower simultaneously in a given place.” Explain.

The flowering in plants is in response to duration period of light or relative length of light. The long day plants need a longer duration of light whereas the short day plants need short duration of light. 

If the long day plant and the short day plants gets the required duration of the light necessary for their flowering they may produce flower simultaneosly in a given plave. If the long day plants is planted before the short day one such that the long day plants gets a longer duration of light , both the short day plant and a long day plant can produce flower simultaneously in a given place

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Would a defoliated plant respond to photoperiodic cycle ? Why ?

No, a defoliated plant will not respond to photoperiodic cycle or stimulus. The photoperiodic is perceived by leaves as, the site of perception of light/dark duration are the leaves, which have been removed in a defoliated plant.
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What would be expected to happen if :

(a) GA3 is applied to rice seedlings.

(b) Dividing cells stop differentiating.

(c) A rotten fruit gets mixed with urripe fruits.

(d) You forget to add cytokinin to the culture medium


(a) The elongation of stem will occur at fast rate.

(b) An undifferentiated mass of cells is formed.

(c) The unripe fruits will ripen quickly.

(d) There will be no differentiation of shoot buds.

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