Q. 53 Identify the INCORRECT statement in connection with polar transport of auxin.
(A) The putative influx carrier AUX1 is a cytosolic protein
(B) Polar auxin transport in root tends to be both acropetal and basipetal in direction
(C) Naphthylphthalamic acid (NPA) is an inhibitor of polar auxin transport
(D) AUX1 and PIN1 proteins are located in the opposite ends of a cell for polar transport
Polar auxin transport regulates plant growth through directed hormone movement, and understanding its mechanisms is key for exams like CSIR NET Life Sciences. This article identifies the incorrect statement from the given options, with detailed explanations.
Correct Answer
The incorrect statement is (A) The putative influx carrier AUX1 is a cytosolic protein. AUX1 functions as a transmembrane protein in the plasma membrane, not the cytosol.
Option Explanations
AUX1 and PIN proteins drive polar auxin transport via asymmetric localization.
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(A) Incorrect: AUX1 is an auxin influx carrier localized to the plasma membrane (apical/basipetal ends), trafficked via endosomal pathways. It is not cytosolic; labeling shows plasma membrane association disrupted only by inhibitors like NPA.
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(B) Correct: Root polar auxin transport shows acropetal (shoot-to-tip in epidermis/stele) and basipetal (tip-to-shoot renewal) directions, mediated by PIN2 (basal in cortex) and PIN1/PIN4.
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(C) Correct: NPA binds efflux carriers (PIN/ABCB), inhibiting polar auxin transport by disrupting protein recycling and localization.
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(D) Correct: In protophloem cells, AUX1 localizes apically (influx), PIN1 basally (efflux), enabling vectorial transport across opposite cell ends.
Exam Relevance
This question tests AUX1/PIN polarity and transport inhibition, common in GATE/CSIR Botany modules. Focus on chemiosmotic model: influx (AUX1/LAX), efflux (PIN/ABCB), and regulators like NPA for scoring.
