Chemical preparation and treatments
1-N-naphthylphthalamic acid (NPA) and yucasin were dissolved in DMSO to make a 50 mM stock solution. For treatment, the required amount of the stock solutions was added into MS salts agar and mixed in uniform before being poured into Petri dishes. Acetoin (≥ 98%, Sigma-Aldrich) was dissolved in DDW to make a 250 mM stock solution and was supplied at different doses (0, 10, 30, 100, 300 and 1000 μM) to the plant growth medium. Petri dishes containing 5 plants under different treatments were placed in growth chamber for 8 d to estimate root development. For investigating the effects of acetoin on CYCB1 expression pattern, prebranch sites formation and LRPs development stage, 3-day-old seedlings were grown with 30 μM acetoin for 6 d.
To test the effects of other VCs from SQR9 on root development, the pure compounds (dodecane, tetradecane, 2-dodecanone, 2-nonanone, pentadecane, 2-undecanone, 2-heptanone) were purchased from Sigma. Arabidopsisseedlings were exposed to a filter paper added with 0, 1, 10 and 100 µl pure compound in a bi-compartmented Petri dish for 8 d to estimate root development.