Materials and Reagents

1. Duckweed fronds, Spirodela polyrrhiza (collected from the paddy field drainage in the Tai Lake region of China)
   
2. Sterile deionized water
   
3. Methanol (HPLC grade) (Sigma-Aldrich, catalog number: 179337)
   
4. Hydrochloric acid (HCl) (Sigma-Aldrich, catalog number: 653799)
   
5. Formaldehyde solution (37 wt.% in H₂O) (Sigma-Aldrich, catalog number: 252549)
   
6. Sodium hypochlorite (NaClO) (available chlorine 4.00-4.99 %) (Sigma-Aldrich, catalog number: 239305)
   
7. 0.15% formaldehyde solution (see Recipes)
   
8. 0.5% v/v NaClO (see Recipes)
   
9. Modified Steinberg nutrient solution (see Recipes)
   

Equipment

1. Duckweed root exudate collection device (Figure 1)
   
   1. Plexiglass pot (D x H, 16 x 16 cm)
      
   2. Glass column (D x H, 23 x 170 mm)
      
   3. XAD-4 resin (20-60 mesh) (Sigma-Aldrich, catalog number: 37380-42-0)
      
   4. Hydrophobic fluoropore (PTFE) membrane (14 x 14 cm)
      
   5. Glass wool (Sigma-Aldrich, catalog number: 18421)
      
   6. Teflon stopper
      
   7. Aluminum foil
      
   8. Silicone tube
      
      
      Figure 1. Equipment used in root exudate collection
   
   
2. Clean bench
   
3. Peristaltic pump
   
4. Rotary evaporator (Tokyo Rikakikai, EYELA, model: N-1100D)
   
5. Freeze dryer (Freezone Plus 2.5) (Labconco)
   
6. Incubation chamber (23 ± 1 °C, under fluorescent lamps at 100 μmol/m/s, 16 h light/8 h dark)
   

Procedure