Question

Spraying sugarcane crops with a plant hormone increases the length of plants and increases yield by as much as 20 tonnes/acre. The hormone is
A) Gibberellin
B) Auxin
C) Cytokinin
D) ABA

Answer 1

Plant hormones are known as some internal or intrinsic factors that regulate the growth and development of plants. These hormones are produced in various parts of plants and transmitted to the other part. They control all the activities like cell division, enlargement, seed formation, abscission, etc.

Complete answer:
Plant hormones are categorized into two categories on the basis of their action- plant promoters and plant inhibitors. Now let us look at the given explanation of given hormones.

A) Gibberellin hormone is a kind of plant promoter. They are acidic in nature. It promotes sudden elongation of dwarf varieties of plants, stem, internodes and development of fruit. It also breaks seed dormancy sugarcane stores carbohydrates as sugar in their stems. So, spraying gibberellin or gibberellic acid on sugarcane crops increases the length of the stems. It results in an increased yield by 20 tonnes/acre.

B) Auxin means 'to grow'. It promotes cell elongation of stems and roots and helps in apical dominance. It prevents the fall of premature leaves, flowers and fruits. It is also a useful stem cutting and grafting process.

C) Cytokinin is also a kind of plant promoter hormone. It promotes lateral and adventitious shoot growth and stimulates the formation of chloroplast in the leaves of the plants. It also plays an important role in the process of cytokinesis.

D) Abscisic acid is a growth inhibitor hormone. It inhibits plant metabolism and seed germination. It is also called a stress hormone because it increases the tolerance of plants.

So, the correct answer is option (A).

Note: Gibberellic acid, ethephon, glyphosine, etc. are some synthetic gibberellins hormones. At present there are more than 830 different gibberellins that are known. Yabuta and Sumuki successfully isolated gibberellic acid in crystalline form. Some active centres of gibberellin synthesis are – embryos, buds, root tips, young leaves, etc.