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Q8(f):
Which one of the plant growth regulators would you use if you are asked to:
(f) induce immediate stomatal closure in leaves.
Solution :
Identification of the Physiological Agent
To induce immediate stomatal closure in leaves, the plant growth regulator required is Abscisic Acid (ABA).
Step 1: Mechanism of Stomatal Action
Stomatal aperture regulation is primarily controlled by the turgor pressure of guard cells. When guard cells are turgid, the stomatal pore is open; when they lose water and become flaccid, the pore closes [Per the Turgor Theory of Stomatal Movement].
Step 2: Signaling Cascade of Abscisic Acid
Abscisic acid functions as a stress hormone, particularly under conditions of water deficit. The physiological induction follows this sequence:
- Perception: ABA binds to PYR/PYL/RCAR receptors located in the plasma membrane and cytosol of guard cells.
- Inhibition: The ABA-receptor complex inhibits Type 2C Protein Phosphatases (PP2Cs), which are negative regulators of the pathway.
- Activation: This releases SnRK2 kinases, which phosphorylate downstream targets, including anion channels (such as SLAC1) and inward-rectifying $K^+$ channels.
- Efflux of Ions: Anion channels open, facilitating the efflux of $Cl^-$ and $NO_3^-$. Simultaneously, the inhibition of inward-rectifying $K^+$ channels prevents $K^+$ uptake, while outward-rectifying $K^+$ channels are activated to facilitate $K^+$ efflux.
Step 3: Osmotic Consequence and Turgor Loss
The rapid efflux of ions ($K^+$, $Cl^-$, $NO_3^-$) from the guard cell cytosol into the apoplast decreases the osmotic potential of the guard cells [Per the Principle of Osmosis]. Consequently, water follows the solute gradient, exiting the cells via aquaporins. The loss of hydrostatic pressure causes the guard cells to lose turgor, leading to the physical closure of the stomatal pore [By the Law of Hydrostatics].
Visual Representation of Stomatal Flux
Comparative Summary of Ion Flux
| Ion Type | Direction of Movement | Resulting Osmotic Potential |
|---|---|---|
| $K^+$ (Potassium) | Efflux (Exit) | Increased (Less negative) |
| $Cl^- / NO_3^-$ | Efflux (Exit) | Increased (Less negative) |
Final Solution: Abscisic Acid (ABA) is the plant growth regulator used to induce immediate stomatal closure.
More Questions from Class 11 Biology Plant Growth and Development EXERCISES
- Q1: Define growth, differentiation, development, dedifferentiation, redifferentiation, determinate growth, meristem and growth rate.
- Q2: Why is not any one parameter good enough to demonstrate growth throughout the life of a flowering plant?
- Q3(a): Describe briefly: (a) Arithmetic growth
- Q3(b): Describe briefly: (b) Geometric growth
- Q3(c): Describe briefly: (c) Sigmoid growth curve
- Q3(d): Describe briefly: (d) Absolute and relative growth rates
- Q4: List five main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural/horticultural applications of any one of them.
- Q5: Why is abscisic acid also known as stress hormone?
- Q6: ‘Both growth and differentiation in higher plants are open’. Comment.
- Q7: ‘Both a short day plant and a long day plant can produce can flower simultaneously in a given place’. Explain.
- Q8(a): Which one of the plant growth regulators would you use if you are asked to: (a) induce rooting in a twig
- Q8(b): Which one of the plant growth regulators would you use if you are asked to: (b) quickly ripen a fruit
- Q8(c): Which one of the plant growth regulators would you use if you are asked to: (c) delay leaf senescence
- Q8(d): Which one of the plant growth regulators would you use if you are asked to: (d) induce growth in axillary buds
- Q8(e): Which one of the plant growth regulators would you use if you are asked to: (e) ‘bolt’ a rosette plant
- Q9: Would a defoliated plant respond to photoperiodic cycle? Why?
- Q10(a): What would be expected to happen if: (a) $GA_3$ is applied to rice seedlings
- Q10(b): What would be expected to happen if: (b) dividing cells stop differentiating
- Q10(c): What would be expected to happen if: (c) a rotten fruit gets mixed with unripe fruits
- Q10(d): What would be expected to happen if: (d) you forget to add cytokinin to the culture medium.
CBSE Solutions for Class 11 Biology Plant Growth and Development
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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