63 Match the above columns involving plant hormones and their signalling pathways:

Column I                        Column II                        Column III
(A) Auxin and                   (a) Trans-                   (i) Response mediated
Gibberellins                      membrane                  by receptor
phosphorylation /
dephosphorylation
(B) Cytokinin                   (b) Soluble                  (ii) Response
and                                receptor                      mediated by
Brassino-                                                              proteasome
steroid                                                            mediated protein
degradation

(1) A-(a)-1 and B-(b)-i                 (2) A-(b)-ii and B-(a)-i
(3) A-(b)-i and B-(a)-i                 (4) A-(a)-ii and B-(b)-i

Correct answer: (2) A-(b)-ii and B-(a)-i

Explanation:

• (A) Auxin and gibberellins signal through soluble receptors inside the cell, leading to responses often mediated by proteasome-dependent protein degradation. This allows them to regulate growth processes by degrading transcriptional repressors or other regulatory proteins.

• (B) Cytokinin and brassinosteroids signal through transmembrane receptors typically located on the cell surface, initiating response pathways mediated by receptor phosphorylation/dephosphorylation cascades.

• Column matching:

  • Auxin & Gibberellins = soluble receptor (b) + proteasome-mediated degradation (ii)

  • Cytokinin & Brassinosteroids = transmembrane receptor (a) + phosphorylation/dephosphorylation (i)

Option-wise:

• (1) A-(a)-i and B-(b)-ii — incorrect pairing.

• (2) A-(b)-ii and B-(a)-i — correct pairing.

• (3) A-(b)-i and B-(a)-i — incorrect (A’s response type).

• (4) A-(a)-ii and B-(b)-i — incorrect.

  Plant hormone signaling involves diverse receptor types and downstream mechanisms: auxin and gibberellins activate gene expression via soluble receptors and regulated protein degradation, whereas cytokinins and brassinosteroids use membrane-bound receptors triggering phosphorylation cascades for growth regulation.