Question

Which endogenous hormone increases under drought conditions?

• A. Auxins
• B. Gibberellic acid
• C. Abscisic acid
• D. Cytokinin

Hint:

Think about which hormone is directly responsible for closing stomata when a plant senses water shortage.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks which naturally occurring plant hormone rises in level when a plant is placed under drought, that is water deficit, stress.

Step 2: Key Formula or Approach:
Plants respond to water shortage through a well studied hormonal signal: as soil and leaf water content fall, roots and leaves sharply increase their production of abscisic acid, commonly abbreviated ABA. ABA is the classic stress hormone of plants and its main visible action is closing the stomata to cut down water loss through transpiration.

Step 3: Detailed Explanation:
Auxins mainly control cell elongation, tropic growth bending and apical dominance, and their level does not rise as the main drought response; if anything, auxin related growth is usually suppressed under stress.
Gibberellic acid mainly drives stem elongation, seed germination and flowering, and its level tends to fall, not rise, under water stress, since growth is generally slowed down when water is short.
Cytokinin mainly promotes cell division and delays leaf senescence, and drought stress typically lowers cytokinin levels, which is part of why drought speeds up leaf yellowing and senescence.
Abscisic acid, in contrast, is synthesized rapidly in roots and transported to the shoot when the plant senses falling water potential, and its rising level triggers stomatal closure and other protective adjustments, making it the hormone that clearly increases under drought.

Step 4: Final Answer:
Abscisic acid is the endogenous hormone that increases under drought conditions.