Plant Growth and Development Test - 53

The hormone abscisic acid is released in the plants during the conditions of stress and so known as the stress hormone. The hormone causes the closing of the stomata, inhibit plant metabolism and seed germination, which increases the tolerance of the plant towards stress. 

Ethephon is the source of the plant growth hormone ethylene. The substance gets soluble in the water and the aqueous solution can be easily transported. Ethylene is slowly released from this solution which allows the ripening of the fruits and causes abscission of the cotton and walnut. 

Gibberellin or gibberellic acid is a plant hormone that was isolated from fungus Gibberella fujikuroi. It promotes internodal cell elongation in the wide range of species. This internodal elongation phenomenon is known as blotting. It has also a role in germination, flowering, and fruit ripening. Thus, the correct answer is option C.

• Pectin is a naturally occurring heteropolysaccharide present in the primary cell walls of plants.
  
• It is a natural fibre found in the cell walls of plants and is mainly found in the fruit skin.
• It is a major component of fruit cell walls that are extensively modified during fruit ripening. 
• This structural component undergoes partial solubilization, depolymerization and the loss of neutral side chains that causes ripening of the fruits.
  
• So, the correct answer is 'Partial solubilisation of pectic compounds'.

Zeatin is the example of the phytohormone cytokinin. The hormone was discovered from the autoclaved herring sperm DNA. The hormone was isolated from the corn kernels and the coconut milk, where the hormone was responsible for cytokinesis. 

• Abscisic acid (ABA) promotes seed and bud dormancy by inhibiting growth. It is one of the most important plant's growth regulators. ABA also plays an important role in the closure of stomata in plants under water stress and its presence inhibits opening.
• Seed dormancy is defined as a state in which seeds are prevented from germinating even under environmental conditions normally favorable for germination.
• Bud dormancy is a process in which plant meristems become mostly inactive to withstand a harsh environment.
  

In 1930s Gibberellin (GA) was first isolated in Japan from a fungus that causes a serious disease in rice, called “foolish seedling disease” (bakanae-byo) by Japanese farmers. Giberella fujikuroi species were found Rice.

In maize seed, which is moncot and endospermic seed. The embryo consists of an upper shield shaped scutellum which is actually a reduced cotyledon.  It secretes certain hormones (ABA and gibberellin) into the endosperm which synthesize enzyme responsible for the breakdown of reserve food materials into soluble forms.

A. Auxin- Responsible for shoot elongation.

B. Cytokinin- promotes cell division.

C. Gibberellin- Stimulate cell elongation,

D. Ethylene- Stimulate and regulate rioening of fruit.

So, the correct answer is 'Giberrellin'.

Cytokinin (CK) is a plant hormone. It promotes cell division and prevents senescence in plants. It improves nutrient mobilization and thus delays leaf senescence. When applied externally, it mobilizes nutrients towards sites of application.