Question

Which one of the following is a gaseous plant hormone?
A) Auxin
B) Gibberellin
C) Ethylene
D) Cytokinin

Answer 1

Used for ripening of fruits, at home especially for bananas, mangoes etc. Also induces flowering in mango and found in large amounts in tissues undergoing senescence and fruit ripening.

Complete answer:
Ethylene is a gaseous plant hormone (phytohormone) produced by almost all parts of plant but meristematic tissues are considered as active sites for its production. Being a gaseous hormone it diffuses to other parts of the plant from its site of synthesis. Ethylene has the simplest structure (C2H4). Its production rate depends on the type of tissue and developmental stage of the plant. Produced from its precursor methionine via S-adenosylmethionine and 1-aminocyclopropane-1-carboxylic acid (ACC). Tissues undergoing senescence and ripening have higher ethylene production. Conditions such as drought, chilling, flooding or mechanical wounding increases the synthesis of ethylene.

Ethylene affects both the growth and development of plants. In terms of growth, regulates the cell size, restricts cell elongation and also regulates cell division. In terms of development, regulates and accelerates the processes such as ripening, senescence, and abscission therefore, sometimes considered an 'aging' hormone. Ethylene perform various physiological functions such as abscission (shedding of leaves, flowers, fruits and other plant organs), flowering (induce flowering in many plants), epinasty (downward curvature of leaves), rooting (adventitious and root hair formation) and fruit ripening (accelerates the process of ripening). Ethylene also promotes the horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. It also assists in germination of seeds by breaking the seed and bud dormancy. Ethylene helps the plants to increase their absorption surface by promoting root growth and root hair formation. Ethephon as a source of ethylene is most widely used in agriculture.

Thus, the correct answer is option C. i.e., Ethylene.

Note: Ethylene is one of the most widely used plant growth hormones in agriculture. Besides having various physiological functions it is famous for ripening of fruits.