It seems like you're asking about the precursor molecules of plant growth regulators (PGRs). There isn't one single answer to this question as PGRs are a diverse group of molecules with various origins and synthesis pathways.

Here's a breakdown of some common PGRs and their precursor molecules:

1. Auxins (e.g., Indole-3-acetic acid (IAA))

* Tryptophan: The most common precursor for IAA.

* Indole-3-pyruvic acid (IPA): An intermediate in the tryptophan pathway.

2. Gibberellins (e.g., Gibberellic acid (GA3))

* Geranylgeranyl diphosphate (GGPP): A key precursor in the terpenoid pathway.

* Ent-kaurene: A diterpene that undergoes several modifications to become active gibberellins.

3. Cytokinins (e.g., Zeatin, kinetin)

* Adenine: The basic building block for cytokinins.

* Isopentenyl adenosine 5'-phosphate (iPA): A precursor in the biosynthesis pathway.

4. Abscisic acid (ABA)

* Zeaxanthin: A carotenoid precursor.

* Violaxanthin: Another carotenoid precursor.

5. Ethylene

* Methionine: The main precursor for ethylene biosynthesis.

6. Brassinosteroids (e.g., Brassinolide)

* Campesterol: A sterol precursor.

Important Note: These are just a few examples, and the specific precursor molecules and pathways can vary depending on the plant species and the specific PGR.

Let me know if you'd like more information on any specific PGR or its biosynthesis pathway!