Delonix regia regulate early seedling development in vitro

Plant-derived secondary metabolites are increasingly investigated as natural regulators of early plant development and as candidates for standardized in vitro screening. Here, we developed an organ-resolved assay to quantify the growth-inhibitory activity of methanolic extracts from stem, leaf, and flower tissues of Delonix regia using a controlled Petri-dish system with Brassica integrifolia as a sensitive test species. Extracts were tested at eight concentrations (0-100 mg mL⁻¹) in a completely randomized design (4 replicates; 50 seeds per replicate), and germination dynamics and seedling performance were recorded after 120 h at 25 °C in darkness. Leaf extract was consistently the most active, reducing germination from 98.67% to 0.00% across the tested range and reaching 100% relative injury at 100 mg mL⁻¹, with complete suppression of root and shoot elongation at higher doses. Dose–response analysis using a four-parameter log-logistic model confirmed strong organ specificity: for root inhibition, leaf extract showed the lowest EC₅₀/EC₉₀ (30.84/42.80 mg mL⁻¹), whereas flower extract was markedly less effective (e.g., RIR EC₉₀ = 301.70 mg mL⁻¹). Chemical profiling further supported these patterns: leaf tissue contained the highest total phenolics (163.62 mg GAE g⁻¹ DW) and accumulated high levels of salicylic acid (442.14 µg g⁻¹ DW) and epigallocatechin gallate (3,860.58 µg g⁻¹ DW). Collectively, these results provide a quantitative, organ-specific in vitro framework integrating standardized phenotyping, dose–response modeling, and high-performance liquid chromatography with diode-array detection (HPLC–DAD) profiling to prioritize active tissues and candidate compounds for downstream mechanistic studies.