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In the absence of cytokinin, cell growth, differentiation of shoot etc will not be observed. 
When a rotten fruit gets mixed with unripe fruits, the ethylene produces by it fastens the ripening of other unripe fruits. 
If dividing cells stop differentiating, then the specialised tissues and plant organs such as leaves and stem will not be formed. Here, the mass of undifferentiated cell is called callus.
If  is applied to rice seedlings, it will cause internode elongation as a result of which, the height of the stem of rice will increase. 
A defoliated plant is the one whose leaves have been removed. The hormone of flowering is produced at the leaves and from here it moves to shoot apices. Thus, in the absence of leaves, the plant will not be able to able to respond to photoperiodic stimulus
Induce immediate stomatal closure in leaves Abscisic acid can be used to induce immediate stomatal closure in leaves. 
‘Bolt’ a rosette plant. Gibberellins are plant hormones that are involved in bolting i.e. stem elongation of rosette plants. 
Induce growth in axillary buds The growth in axillary buds can be induced by cytokinins. 
Delay leaf senescence Cytokinins are used to delay leaf senescence in plants. 
Quickly ripen a fruit Ethylene is responsible for inducing ripening in fruits. Thus to quickly ripen a fruit, ethylene can be used
Induce rooting in a twig To induce rooting in a twig auxin will be used as auxins are helpful in root formation. 
The process of flowering in short-day plants and long-day plants is dependent on the photoperiod i.e. the duration for which these plants are exposed to light. Both a short day plant and a long day plant can produce flower simultaneously in a given place if they have been provided with an adequate photoperiod.
The process of growth in plants is indefinite due to the presence of meristems. Thus, growth and differentiation in them can occyr at any time. this is the reason why the process of growth and differentiation in higher plants is referred to as being open.
Abscisic acid is responsible for the induction of various responses in plants against stress conditions. It can increase the tolerance of plants toward various stresses. It also induces the closure of the stomata during water stress and promotes seed dormancy and ensures seed germination during favourable conditions. Abscisic acid is helpful for seeds to withstand desiccation. It also helps in...
Photoperiodism- It is the effect of photoperiods or day duration of light hours on the growth and development of a plant, especially flowering. On the basis of photoperiodic response, flowering plants have been divided into the following categories- 1. Short Day Plants– These plant flower when the photoperiod is below a critical period (continuous duration of light which must not be exceeded in...
Five main groups of plant growth regulators are auxin, gibberellins, cytokinins, abscisic acid and ethylene.  Discovery of GIbberellin Gibberellins were discovered in Japan from rice plants suffering from bakane  or foolish seedling disease. Such rice plants were thin, pale green spindle-shaped, longer by 50 % than the healthy plants and were sterile.. The disease was found by Hori and Kurosawa...
Absolute growth rate refers to the measurement and comparison of total growth per unit time. Relative growth rate refers to the growth of a particular system per unit time, expressed on a common basis.
Sigmoid growth curve- The growth of living organisms in their natural environment is characterised by an S-shaped curve called the sigmoid growth curve when growth is plotted against time. This curve is divided into three phases — lag phase, log phase or exponential phase of rapid growth, and stationary phase.
Geometric growth- This growth is characterised by slow growth in the initial stages and rapid growth during the later stages. The daughter cells derived from mitosis retain the ability to divide but slow down because of limited nutrient supply.
Arithmetic growth- In arithmetic growth, one of the daughter cells continues to divide, while the other differentiates to become mature and perform its speacialised function. The elongation of roots at a constant rate is an example of arithmetic growth.