- Dark grown Arabidopsis seedlings show ‘triple response’ when exposed to ethylenehormone. Which one of the following options is characteristic of ‘triple response’?
(1) Reduced shoot elongation, increased shoot thickness and tightening of apical hook.
(2) Reduced shoot elongation, reduced shoot thickness and loosening of apical hook.
(3) Increased shoot elongation, increased shoot thickness and loosening of apical hook.
(4) Increased shoot elongation, reduced shoot thickness and tightening of apical hook.
Correct answer: (1) Reduced shoot elongation, increased shoot thickness and tightening of apical hook
Explanation:
-
The triple response of dark-grown Arabidopsis seedlings exposed to ethylene consists of:
-
Reduced shoot (hypocotyl) elongation
-
Increased shoot thickness (radial swelling)
-
Tightening or exaggeration of the apical hook
-
-
The other options describe either loosening of the apical hook or increased elongation, which are not characteristics of the triple response.
Option-wise:
-
(1) Correct; matches the known triple response phenotype.
-
(2) Incorrect; apical hook loosening and reduced thickness are opposite to triple response.
-
(3) Incorrect; increased elongation is not part of triple response.
-
(4) Incorrect; increased elongation and reduced thickness are not triple response traits.
Ethylene triggers the triple response in dark-grown seedlings marked by shortened, thickened hypocotyls and a tightly curled apical hook, a morphological adaptation aiding soil emergence and protection of shoot apices.
