Plant Growth and Development Test - 9

Gibberellic acid breaks seed dormancy by activating enzyme $$\alpha$$ - amylase. While abscisic acid and phenolic acid induce seed dormancy.

Growth occurs in three phases namely lag phase (slow growth phase), Log phase or exponential growth phase and steady or plateau or stationary phase.

Abscisic acid (ABA) is a growth inhibitor. Both auxins and cytokinins are essential for morphogenesis or differentiation of tissues and organs. Auxins stimulate root formation however when cytokinins are in-excess stem buds develop. 

Natural cytokinins are synthesized primarily in the meristematic region of the roots, that divide rapidly.

Solution:

• Correct answer is option B.
• Explanation for correct option:
•  Gibberellin is a phytohormone which is usually found in acidic nature and hence called as gibberellic acid.
• Gibberellins have role in promoting seed germination.
• Action of mechanism is gibberellins induce production of hydrolysing enzymes.  
• When these hydrolysing enzymes in endosperm are produced, they in turn stimulates the production of digestive enzymes like proteases, amylase and lipase which help to mobilise stored nutrients. Thus inducing the seed germination. 

Auxin is a plant hormone (phytohormone). It is used in various processes of plant development. IAA and IBA are naturally occurring auxin hormone. NAA is a synthetic phytohormone. These hormone enhances fruit setting and helps in producing seedless, larger and sweeter fruits. Fruits like orange, banana are produced seedless using these hormones. These hormones also help in early maturing of fruits, thinning of blossoms. They also prevent early fruit fall before harvesting. 

• Cytokinins give the 'Richmond Lang effect', by which the aging (senescence) is delayed in plants. 
• It happened because of the retardation in the destruction of chlorophyll, etc. 
• Thus, it helps in the reduction of leaf fall.

Auxins promote stem elongation.

• Ethylene is the only gaseous phytohormone, which stimulates transverse or isodiametric growth but retards the longitudinal one. 
• It is a gas that forms through the breakdown of methionine, which is present in all cells. 
• It has very limited solubility in water and does not accumulate within the cell but diffuses out of the cell and escapes out of the plant.

Maximum growth of root takes place in the back side portion of the root apex. Apex portion is made up of root cap and then follows the region of cell division where meristematic tissue is present.