Physicochemical Properties and Identification of Natural Brassinolide

【Common Name】Brassinolide

【Molecular Formula】C28H46O6

【Molecular Weight】480.68

【Physicochemical Properties】White crystalline powder; melting point 256–258°C; solubility in water 5 mg/kg; readily soluble in organic solvents such as methanol, ethanol, and acetone.

【Toxicity】Low toxicity. Acute oral LD50 in rats >2000 mg/kg; acute oral LD50 in mice >1000 mg/kg (technical grade).

【Category】Plant growth regulator.

【Common Formulations】95% technical grade; 0.01% emulsifiable concentrate (EC); 0.04% and 0.1% aqueous solutions (AS); 0.2% soluble powder (SP).

【Identification】

(1) Physical Identification (Sensory): Wettable powder appears as a white powdery solid; emulsifiable concentrate and aqueous solution appear as uniform, transparent liquids.

Schematic diagram of the rice leaf inclination method for Brassinolide identification

(2) Biological Identification: Rice leaf inclination method.
Use etiolated rice seedlings (germinated until the radicle/coleoptile tip emerges) that have been cultured in the dark at a constant temperature of 30°C for 7 days. Under dim red light (e.g., a 15W incandescent bulb wrapped in 1–2 layers of red plastic paper or film), excise a segment centered on the leaf joint (pulvinus) of the first fully expanded leaf (also known as the second leaf), ensuring the segment includes 1 cm of the leaf blade and 1 cm of the leaf sheath. Rinse the segments in distilled water for 24 hours, then select segments with a uniform initial angle. Immerse the root-end (i.e., the leaf sheath end) of each segment into 1 mL of treatment solution: Solution No. 1 is distilled water (control), and Solution No. 2 is the Brassinolide sample to be identified at a concentration of 10 µg/L. After incubating in the dark at 30°C for 48 hours, use a transparent protractor to measure the supplementary angle of the angle formed between the leaf blade and the leaf sheath. If the leaf exhibits the change in inclination shown in the figure, it demonstrates that Treatment Solution No. 2 contains brassinolide.