what are plant growth regulator
Answers
NCERT based Answer for Class 11 Biology Students
Plant Growth Regulators (PGRs): These are organic compounds that are capable of influencing physiological activities leading to promotion, inhibition and modification of growth.
Functions of Auxins:
Initiate rooting in stem cuttings.
Promote flowering. Example: In pineapple.
Prevent fruit and leaf drop at early stages.
Induce parthenocarpy, example: seedless tomato.
Widely used as herbicide. 2, 4- D widely used to kill dicotyledonous weeds, does not affect mature monocot plants (wheat, rice, corn).
The growing apical bud inhibits growth of lateral buds by releasing auxins. This phenomenon is called apical dominance. Removal of shoot tips (decapitation) results in growth of lateral buds. It is widely applied in tea plantation and hedge making.
Functions of Gibberellins:
Cause increase in length of axis, example: increase length of grapes stalk.
Cause fruits like apple to elongate and improve its shape.
Delay senescence. Thus fruits can be left on the tree longer so as to extend the market period.
GA3 is used to speed up malting process in brewing industry.
Spraying sugarcane crop with gibberellins increases length of stem, thus increasing yield by as much as 20 tonnes per acre.
Gibberellins promote bolting (internodes elongation just prior to flowering) in beet, cabbage and many plants with rosette habit.
Functions of Cytokinins:
It helps produce new leaves, chloroplasts in leaves and lateral shoot growth.
Cytokinins help overcome the apical dominance.
Promote nutrient mobilisation which helps in delay of leaf senescence.
In tissue culture, differentiation of callus occurs in presence of auxin and cytokinins.
Ethylene (A gaseous PGR) is synthesised by tissues undergoing senescence and ripening fruits.
Functions of Ethylene:
Promotes senescence and abscission in leaves and flowers.
Causes fruits ripening.
Enhances respiration rate during ripening of fruits. This rise is rate of respiration is called respiratory climactic.
Breaks seed and bud dormancy, initiates germination in peanut seeds, sprouting of potato tubers.
Promotes rapid internode elongation in deep water rice plants. It helps leaves to remain above water.
Promotes root growth and root hair formation, thus helping plants to increase their absorption surface.
Initiates flowering in pineapple and mango.
Promotes female flowers in cucumber, thus increasing the yield.
Note: Since it regulates so many physiological processes, it is one of the most widely used PGR in agriculture. The most commonly used compound as source of ethylene is ethephon. Ethephon in an aqueous solution is readily absorbed and transported within plant and releases ethylene slowly. Ethephon hastens fruit ripening in tomatoes and apples. It accelerates abscission in flowers and fruits; i.e. thinning of cotton, cherry, walnut. It allows better growth of remaining fruits.
Abscisic Acid (ABA):
Inhibits seed germination.
Stimulates closure of stomata and increases tolerance of plants to various stresses. Therefore, it is also called the stress hormone.
By inducing dormancy, ABA helps seeds to withstand desiccation and other factors unfavourable for growth.
If you find the answer useful, plz mark it the Brainliest.
Visit our website for purchasing XI & XII Complete Syllabus Video Lectures
https://concept-tutorials.teachable.com
