- Dark grown Arabidopsis seedlings when exposed to ethylene gas shows typical triple response. Following are certain statements regarding the triple response:
A. A dominant ethylene receptor mutant will not show triple response in the presence of ethylene.
B. Tightening of apical hook is one of the features of triple response.
C. Loss of function of multiple receptors will show triple response even in the absence of ethylene.
D. Increase in hypocotyl length is a feature of triple response.
Which one of the following combinations is correct?
(1) A, B and C (2) A, C and D
(3) B, C and D (4) A, B and D
Correct answer: (1) A, B and C
Explanation:
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(A) A dominant ethylene receptor mutant is typically insensitive to ethylene and thus will not show the triple response in the presence of ethylene. This is correct.
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(B) Tightening (or exaggeration) of the apical hook is a classic, defining feature of the ethylene triple response in dark-grown seedlings. True.
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(C) Loss of function of multiple ethylene receptors leads to a constitutive triple response even in the absence of ethylene because the repression of the pathway is lost. True.
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(D) Increase in hypocotyl length is opposite to the triple response, which actually causes reduced hypocotyl elongation. Hence, D is false.
Option-wise:
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(1) A, B and C — correct.
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(2) A, C and D — D incorrect.
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(3) B, C and D — D incorrect.
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(4) A, B and D — D incorrect.
Ethylene signaling mutants reveal that insensitive receptor mutants lack the triple response, while receptor loss-of-function mutants display constitutive triple response, characterized by inhibited elongation, hypocotyl thickening, and apical hook tightening, illustrating critical regulation of ethylene pathway.
