Question

The elongation of generally dwarf plants is brought about by application

of ...................

• A. Cytokinins
• B. Gibberellins
• C. X - rays
• D. Vitamin C

Answer 1

The correct option is B Gibberellins

Gibberellins are growth promoting phytohormones. Gibberellins promote stem elongation in many plants. When gibberellin is applied to a plant, particularly certain dwarf varieties, this elongation may be spectacular. Some corn and pea plants that are dwarfs as a result of one or more mutations grow to a normal height when treated with gibberellin. Short-stemmed, high-yielding varieties of wheat have short stems because they have a reduced response to gibberellin. These varieties put less of their resources into stem height and more resources into grain production. Gibberellins are also involved in bolting, the rapid elongation of a floral stalk that occurs naturally in many plants when they initiate flowering.Gibberellins cause stem elongation by stimulating cells to divide as well as to elongate. The actual mechanism of cell elongation differs from that caused by auxin, however. Auxins like indole acetic acid (IAA) induced cell elongation involves the acidification of the cell wall. In gibberellin-induced cell elongation, cell wall acidification does not occur; biologists do not yet know how gibberellins modify cell wall properties to cause cell elongation.