• Strigolactones are a class of carotenoid-derived phytohormones synthesized primarily in roots.
• Their defining endocrine physiological function in plant architecture is the inhibition of shoot branching (axillary bud outgrowth).
• Mutants deficient in strigolactone biosynthesis or signaling (such as max in Arabidopsis, rms in pea, d in rice) display an excessively branched/tillering bushy phenotype.
• Exogenously applied strigolactone restores wild-type branching suppression.
• Therefore, strigolactones regulate shoot branching (Option 2).

• In plant physiology, plant growth regulators that suppress vegetative growth are technically categorized into growth inhibitors and growth retardants:
• Growth Inhibitors: Chemical substances that completely halt or suppress specific physiological processes such as cell division or polar hormone transport. Examples include Maleic Hydrazide (MH) (blocks cell division, used as onion/potato sprout inhibitor) and 2,3,5-Triiodobenzoic acid (TIBA) (blocks polar auxin transport).
• Growth Retardants: Chemicals that slow down cell division and elongation without causing malformations or killing meristems, primarily acting as gibberellin biosynthesis inhibitors. Examples include Chlormequat chloride (CCC / Cycocel) and Paclobutrazol (Cultar).
• Therefore, the synthetic inhibitors among the choices are (A) Maleic Hydrazide and (D) Triiodobenzoic acid (Option 2).

Regulation of synchronous flowering in pineapple (Ananas comosus):

• Commercial pineapple crops exhibit highly erratic, asynchronous natural flowering.
• Application of synthetic auxins such as Naphthalene Acetic Acid (NAA, 10–20 ppm) or ethylene-releasing agents (Ethephon) stimulates endogenous ethylene biosynthesis at the shoot apical meristem, triggering synchronized flower induction across the entire plantation.