61. Following are some statements regarding plant growth hormones.
    A. Ethylene regulates abscission.
    B. Gibberlins do not play any role in flowering

C. Auxin and cytokinin promote cell division.
D. Over expression of cytokinin oxidase would promote root growth
E. ABA inhibits root growth and promotes shoot growth at   low water potential.
F. ABA promotes leaf senescence independent of ethylene.

Which one of the following combination of above statements is correct?
(1) A, C and F        (2) B, C and D
(3) D, E and f        (4) B, D, and E

Correct answer: (1) A, C and F

Explanation:

• (A) Ethylene regulates abscission, the process by which plants shed leaves, flowers, or fruits. This is a well-established role of ethylene.

• (B) Gibberellins do play a role in flowering, especially in promoting flowering in some plants, so this statement is false.

• (C) Auxin and cytokinin promote cell division. Cytokinins directly stimulate cell division, and auxins work synergistically in growth regulation.

• (D) Overexpression of cytokinin oxidase would reduce cytokinin levels leading to inhibited shoot growth and generally less root growth, thus this statement is incorrect.

• (E) ABA typically inhibits shoot growth and promotes root growth at low water potential, reversing the given statement. So this statement is false.

• (F) ABA promotes leaf senescence independent of ethylene, which is true based on several studies showing ABA’s role in aging.

Option-wise:

• (1) A, C and F — correct.

• (2) B, C and D — B and D incorrect.

• (3) D, E and F — D and E incorrect.

• (4) B, D and E — all incorrect.

  Ethylene controls abscission processes, auxin and cytokinins synergize in cell division, and ABA promotes leaf senescence independently of ethylene. Gibberellins influence flowering, and cytokinin oxidase expression modulates hormone levels affecting growth dynamics.