7. The following statements are made regarding cytokinin (CE) biosynthesis plants:
   A.Trans-zeatin (tZ) and iso-pentenyladenile (iP) are common active forms of isoprenoid CKs.
   B. CKs are present as nucleoside and glycosidic conjugates but not as nucleotide conjugates.
8. Dephosphorylation and deribosylation Steps are involved in two-step pathway for active CK formation.
   D. Lonely Guy (LOG) enzyme , involved in CK metabolism

Which one of the following options represents the combination of all correct statements?
(1)A, B and C         (2) A, Band D
(3) A, C and D(4) B, C and D

Introduction

Cytokinins (CKs) are adenine-derived plant hormones controlling cell division, shoot growth, and developmental patterning. Their activity depends on both side-chain structure and conjugation state, and several enzymes—including the LONELY GUY (LOG) family—control conversion between inactive nucleotide precursors and active free bases.

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Evaluation of Each Statement

Statement A

“Trans-zeatin (tZ) and iso-pentenyladenine (iP) are common active forms of isoprenoid CKs.”

• Correct. Isoprenoid cytokinins in plants include N⁶-(Δ²-isopentenyl)adenine (iP) and trans-zeatin (tZ) among the principal active free-base species.

• These forms bind cytokinin receptors and trigger downstream signaling.
  → A is true.

Statement B

“CKs are present as nucleoside and glycosidic conjugates but not as nucleotide conjugates.”

• Incorrect. Plant cytokinins occur as free bases, nucleosides, and nucleotides (riboside 5′-monophosphates), as well as various N- and O-glucosides.

• Nucleotide forms (e.g., iPRMP, tZRMP) are key biosynthetic precursors that LOG enzymes convert into active bases.
  → B is false.

Statement C

“Dephosphorylation and deribosylation steps are involved in two-step pathway for active CK formation.”

• Correct. Besides the direct LOG pathway, a LOG-independent route activates cytokinins by first dephosphorylating cytokinin nucleotides to nucleosides (nucleotidase) and then removing ribose (deribosylation) via nucleosidase, yielding the active base.
  → C is true.

Statement D

“Lonely Guy (LOG) enzyme, involved in CK metabolism”

• Correct. LOG proteins are cytokinin riboside 5′-monophosphate phosphoribohydrolases that convert inactive cytokinin nucleotides directly to active free-base forms (e.g., iP, tZ) in one step, a central part of cytokinin biosynthesis/activation.
  → D is true.

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Why Option (3) Is Correct

• True statements: A, C, D

• False statement: B (because CKs clearly exist as nucleotide conjugates).

Therefore, the correct combination is option (3): A, C and D.