2.4. Extraction and quantification of soluble carbohydrates
Soluble carbohydrates were extracted from 1 g (wet plant
biomass) of floating and submerged leaves by homogenization in
2 mL of 80% (v/v) ethanol with a mortar and pestle. The homogenate
was heated in a water bath at 75 ◦C for 10 min and the insoluble
fraction removed by centrifugation at 5000 × g for 10 min.
The precipitate was resuspended in 2 mL of 80% (v/v) ethanol and
centrifuged again. Supernatants were pooled and dried under a
stream of hot air. Resulting residue was resuspended in 1 mL of
distilled water and desalted by filtration through an ion-exchange
column (Amberlite MB3, England). Sucrose was determined by
the protocol of Cardini et al. [40] and fructose by the method
of Roe and Papadopoulos [41]. Glucose was determined using a
glucose–oxidase–peroxidase coupled assay according to Jorgensen
and Andersen [42]. Soluble sugars were expressed as mg g−1 FW.